WO2025049552A1

WO2025049552A1 - Optical fiber converters

Info

Publication number: WO2025049552A1
Application number: PCT/US2024/044152
Authority: WO
Inventors: Scott Robertson Bickham; Chenueh Abongwa Florian LOHSE; Andreas Matiss; Garth Weber Scannell; Yin SHU
Original assignee: Corning Research and Development Corp
Current assignee: Corning Research and Development Corp
Priority date: 2023-08-30
Filing date: 2024-08-28
Publication date: 2025-03-06
Anticipated expiration: 2026-02-28
Also published as: TW202518086A

Abstract

An optical fiber converter includes a planar fiber interface and a two-dimensional fiber interface. The planar fiber interface defines a single row of openings configured to receive a plurality of optical fibers. The two-dimensional fiber interface is spaced from the planar fiber interface by a spacing and defines at least a first row of openings and a second row of openings configured to receive the plurality of optical fibers from the planar fiber interface. When assembled with the plurality of optical fibers: a first portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the first row of openings of the two-dimensional fiber interface and a second portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the second row of openings of the two-dimensional fiber interface.

Description

OPTICAL FIBER CONVERTERS Related Applications [0001] This application claims the benefit of priority of U.S. Provisional Application Serial No.63/535,525 filed on August 30, 2023, the content of which is relied upon and incorporated herein by reference in its entirety. Field [0002] The present specification generally relates to optical fiber converters and, in particular, optical fiber converters which convert a one-dimensionally pitched fiber array into a two- dimensionally pitched fiber array. Background [0003] For next generation photonic integrated circuits in co-packaging applications, a vast number of optical interconnects in a constrained space are required. Generally, higher level of integration is desired with compatibility to standard fiber optical connectivity. Conventionally, high fiber count fiber-to-chip attachments are done with fiber-array-units. Such assemblies can include significantly more than 24 fibers which are aligned in a v-groove array (in, e.g., a one- dimensional array) facing the photonic integrated circuit (“PIC”)-side and terminated with standard optical connectors (in, e.g., a two-dimensional array) at the other end. These units may be actively aligned and coupled to the PIC and permanently fixed in place. With PICs moving into co-packaging applications, the need emerges to remove optical fiber pigtails and provide an optical connector interface right at the PIC or fiber array unit (“FAU”) level. SUMMARY [0004] Embodiments of the present disclosure are directed to optical fiber converters that converts a one-dimensionally pitched fiber array into a two-dimensionally pitched fiber array while maintaining small form factor. [0005] According to a first aspect A1, an optical fiber converter comprises a planar fiber interface defining a single row of openings configured to receive a plurality of optical fibers; and a two-dimensional fiber interface spaced from the planar fiber interface by a spacing and defining at least a first row of openings and a second row of openings configured to receive the plurality of optical fibers from the planar fiber interface, wherein, when assembled with the plurality of optical fibers: a first portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the first row of openings of the two-dimensional fiber interface; a second portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the second row of openings of the two-dimensional fiber interface. [0006] A second aspect A2 includes the optical fiber converter according to the first aspect A1, wherein the spacing comprises a transition width (w) less than or equal to about 20 mm. [0007] A third aspect A3 includes the optical fiber converter according to the first aspect A1 or the second aspect A2, wherein the first row of openings and the second row of openings are separated by a row height (hr) and wherein the row height (hr) is less than or equal to about 1 mm and greater than or equal to about 0.25 mm. [0008] A fourth aspect A4 includes the optical fiber converter according to any of the aspects A1-A3, wherein the planar fiber interface defines a first pitch between openings of the single row of openings; the two-dimensional fiber interface defines a second pitch between openings of the first row of openings and between openings of the second row of openings; and the first pitch is different from the second pitch. [0009] A fifth aspect A5 includes the optical fiber converter according to the aspect A4, wherein the second pitch is less than or equal to 300 ^m. [0010] A sixth aspect A6 includes the optical fiber converter according to any of the aspects A1-A5, wherein the single row of openings is provided by a v-groove array formed within a top surface of the planar fiber interface. [0011] A seventh aspect A7 includes the optical fiber converter according to any of the aspects A1-A6, wherein each of the planar fiber interface and two-dimensional fiber interface define at least 16 openings. [0012] An eighth aspect A8 includes the optical fiber converter according to any of the aspects A1-A7 and further comprises a bridge attaching the planar fiber interface to the two-dimensional fiber interface. [0013] A ninth aspect A9 includes the optical fiber converter according to any of the aspects A1-A8, wherein the two-dimensional fiber interface comprises a first plate defining a first v- groove pattern and a second plate defining a second v-groove pattern. [0014] A tenth aspect A10 includes the optical fiber converter according to the ninth aspect A9, wherein the two-dimensional fiber interface comprises a spacer plate between the first plate of the two-dimensional fiber interface and the second plate of the two-dimensional fiber interface. [0015] An eleventh aspect A11 includes the optical fiber converter according to the ninth aspect A9, wherein the first v-groove pattern and the second v-groove pattern are interleaved to provide an interleaved v-groove array. [0016] A twelfth aspect A12 includes the optical fiber converter according to any of the aspects A1-A11, wherein the two-dimensional fiber interface defines a guide hole configured to house an alignment pin. [0017] A thirteenth aspect A13 includes the optical fiber converter according to any of the aspects A1-A12, wherein the two-dimensional fiber interface further defines a third row of openings configured to receive the plurality of optical fibers from the planar fiber interface, wherein, when assembled with the plurality of optical fibers, a third portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the third row of openings of the two-dimensional fiber interface. [0018] According to a fourteenth aspect B1, an optical fiber converter comprises a planar fiber interface defining a single row of openings configured to receive a plurality of optical fibers; a two-dimensional fiber interface spaced from the planar fiber interface by a spacing and defining at least a first row of openings and a second row of openings configured to receive the plurality of optical fibers from the planar fiber interface; and a plurality of optical fibers housed within the planar fiber interface as a planar fiber array and within the two-dimensional fiber interface as a two-dimensional fiber array and extending between the planar fiber interface and the two- dimensional fiber interface, wherein: a first portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the first row of openings of the two- dimensional fiber interface; a second portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the second row of openings of the two-dimensional fiber interface. [0019] A fifteenth aspect B2 includes the optical fiber converter according to the fourteenth aspect B1, wherein at least some optical fibers of the plurality of optical fibers comprise, within the spacing, a sigmoidal shape defined by ^

wherein: h is a transition height of the optical fiber; y is a vertical position of the optical fiber equal to 0 at a height of the planar fiber interface; the spacing comprises a transition width (w); z is a position of the optical fiber between an interior surface of the planar fiber interface and an interior surface of the two-dimensional fiber interface, wherein z is equal to, at the interior surface of the planar fiber interface, -0.5w and equal to, at the interior surface of the two-dimensional fiber interface, +0.5w; and l₀ is a length scaling parameter. [0020] A sixteenth aspect B3 includes the optical fiber converter according to the fourteenth aspect B1, wherein at least some optical fibers of the plurality of optical fibers comprise, within the spacing, a sigmoidal shape defined by: ^ ൌ

^^ wherein: h is a transition height of the optical fiber; y is a vertical position of the optical fiber equal to 0 at a height of the planar fiber interface; the spacing comprises a transition width (w); z is a position of the optical fiber between an interior surface of the planar fiber interface and an interior surface of the two-dimensional fiber interface, wherein z is equal to, at the interior surface of the planar fiber interface, -0.5w and equal to, at the interior surface of the two-dimensional fiber interface, +0.5w; and l₁ is a length scaling parameter. [0021] A seventeenth aspect B4 includes the optical fiber converter according to any of the aspects B1-B3, wherein a flexible material encapsulating the plurality of optical fibers is positioned within the spacing. [0022] An eighteenth aspect B5 includes the optical fiber converter according to the seventeenth aspect B4, wherein the flexible material comprises an adhesive. [0023] A nineteenth aspect B6 includes the optical fiber converter according to any of the aspects B1-B7, wherein each optical fiber of the plurality of optical fibers comprises a macrobend loss less than or equal to 0.2 dB. [0024] A twentieth aspect B7 includes the optical fiber converter according to any of the aspects B1-B8, wherein each optical fiber of the plurality of optical fibers comprises a fiber cladding diameter greater than or equal to 50 ^m and less than or equal to 125 ^m. [0025] A twenty-first aspect B8 includes the optical fiber converter according the twentieth aspect B7, wherein the fiber cladding diameter is less than or equal to 100 ^m. [0026] A twenty-second aspect B9 includes the optical fiber converter according to the twenty- first aspect B8, wherein the fiber cladding diameter is less than or equal to 80 ^m. [0027] A twenty-third aspect B10 includes the optical fiber converter according to the twenty- second aspect B9, wherein the fiber cladding diameter is less than or equal to 62.5 ^m. [0028] A twenty-fourth aspect B11 includes the optical fiber converter according to any of the aspects B1-B10, wherein the spacing comprises a transition width (w) less than or equal to about 20 mm. [0029] A twenty-fifth aspect B12 includes the optical fiber converter according to any of the aspects B1-B11, wherein the first row of openings and the second row of openings are separated by a row height (hr) and wherein the row height (hr) is less than or equal to about 1 mm and greater than or equal to about 0.25 mm. [0030] A twenty-sixth aspect B13 includes the optical fiber converter according to any of the aspects B1-B12, wherein: the planar fiber array comprises a first pitch; the two-dimensional fiber array comprises a second pitch; and the first pitch is different from the second pitch. [0031] A twenty-seventh aspect B14 includes the optical fiber converter according to the twenty-sixth aspect B13, wherein the second pitch is less than or equal to 300 ^m. [0032] A twenty-eighth aspect B15 includes the optical fiber converter according to any of the aspects B1-B14, wherein the single row of openings is provided by a v-groove array formed within a top surface of the planar fiber interface. [0033] A twenty-ninth aspect B16 includes the optical fiber converter according to any of the aspects B1-B15, wherein each of the planar fiber interface and two-dimensional fiber interface define at least 16 openings. [0034] A thirtieth aspect B17 includes the optical fiber converter according to any of the aspects B1-B16 and further comprises a bridge attaching the planar fiber interface to the two-dimensional fiber interface. [0035] A thirty-first aspect B18 includes the optical fiber converter according to any of the aspects B1-B17, wherein the two-dimensional fiber interface comprises a first plate defining a first v-groove pattern and a second plate defining a second v-groove pattern. [0036] A thirty-second aspect B19 includes the optical fiber converter according to the thirty- first aspect B18, wherein the two-dimensional fiber interface comprises a spacer plate between the first plate of the two-dimensional fiber interface and the second plate of the two-dimensional fiber interface. [0037] A thirty-third aspect B20 includes the optical fiber converter according to the thirty-first aspect B18, wherein the first v-groove pattern and the second v-groove pattern are interleaved to provide an interleaved v-groove array. [0038] A thirty-fourth aspect B21 includes the optical fiber converter according to any of the aspects B1-B10, wherein the two-dimensional fiber interface defines a guide hole configured to house an alignment pin. [0039] A thirty-fifth aspect B22 includes the optical fiber converter according to any of the aspects B1-B21, wherein the two-dimensional fiber interface further comprises a third row of openings configured to receive the plurality of optical fibers from the planar fiber interface, wherein, when assembled with the plurality of optical fibers, a third portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the third row of openings of the two-dimensional fiber interface. [0040] According to a thirty-sixth aspect C1, a method for converting a planar fiber array to a two-dimensional fiber array comprises: arranging a plurality of optical fibers in a single row of openings of a planar fiber interface, wherein the plurality of optical fibers are arranged within the planar fiber interface as a planar fiber array; extending a first portion of optical fibers of the plurality of optical fibers from the planar fiber interface, across a spacing, and into a first row of openings of a two-dimensional fiber interface; and extending a second portion of optical fibers of the plurality of optical fibers from the planar fiber interface, across the spacing, and into a second row of openings of the two-dimensional fiber interface; wherein the spacing separates the planar fiber interface and the two-dimensional fiber interface and wherein the plurality of optical fibers is arranged within the two-dimensional fiber interface as a two-dimensional fiber array. [0041] A thirty-seventh aspect C2 includes the method according to the thirty-sixth aspect C1 and further comprises coupling a first optical element to an exterior surface of the planar fiber interface. [0042] A thirty-eighth aspect C3 includes the method according to the aspect C1 or the aspect C2 and further comprises coupling a second optical element to an exterior surface of the two- dimensional fiber interface. [0043] A thirty-ninth aspect C4 includes the method according to the thirty-eighth aspect C3 and further comprises extending at least one alignment pin of the second optical element through at least one guide hole of the two-dimensional fiber interface. [0044] A fortieth aspect C5 includes the method according to any of the aspects C1-C4 and further comprises extending a third portion of optical fibers of the plurality of optical fibers from the planar fiber interface, across the spacing, and into a third row of openings of the two- dimensional fiber interface. [0045] A forty-first aspect C6 includes the method according to any of the aspects C1-C5 and further comprises positioning a material within the spacing, wherein the material encapsulates the plurality of optical fibers within the spacing. [0046] A forty-second aspect C7 includes the method according to any of the aspects C1-C6 and further comprises applying an adhesive to attach the plurality of optical fibers to the planar fiber interface. [0047] A forty-third aspect C8 includes the method according to any of the aspects C1-C7 and further comprises applying an adhesive to attach the plurality of optical fibers to the two- dimensional fiber interface. [0048] A forty-fourth aspect C9 includes the method according to any of the aspects C1-C8 and further comprises attaching a first plate of the two-dimensional fiber array to a second plate of the two-dimensional fiber array, wherein the first row of openings and the second row of openings are formed from gaps between the first plate and the second plate. [0049] A forty-fifth aspect C10 includes the method according to any of the aspects C1-C8 and further comprises attaching a first plate of the two-dimensional fiber array to a spacer plate and attaching a second plate of the two-dimensional fiber array to the spacer plate, wherein the first row of openings is formed by gaps between the first plate and the spacer plate and wherein the second row of openings is formed by gaps between the second plate and the spacer plate. [0050] A forty-sixth aspect C11 includes the method according to any of the aspects C1-C10 and further comprises attaching a plate to a surface of the planar fiber interface, wherein the plurality of optical fibers are arranged between the plate and the surface of the planar fiber interface. [0051] Additional features and advantages of the optical fiber converters described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. [0052] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS [0053] FIG. 1A schematically depicts an optical fiber converter, according to one or more embodiments shown and described herein; [0054] FIG.1B schematically depicts the optical fiber converter of FIG.1A coupled to a first optical element and a second optical element, according to one or more embodiments described herein; [0055] FIG. 2A schematically depicts a planar fiber interface, according to one or more embodiments shown and described herein; [0056] FIG.2B schematically depicts a two-row two-dimensional fiber interface, according to one or more embodiments shown and described herein; [0057] FIG. 3 schematically depicts a side view of a fiber extending between a planar fiber interface and a two-dimensional fiber interface, according to one or more embodiments shown and described herein; [0058] FIG.4 schematically depicts a front perspective view of an optical fiber converter having a bridge attaching a planar fiber interface and a two-row, two-dimensional fiber interface, according to one or more embodiments shown and described herein; [0059] FIG. 5 schematically depicts a front perspective view of an optical fiber converter of FIG.4 further including a lid, according to one or more embodiments shown and described herein; [0060] FIG. 6 schematically depicts a front perspective view of an optical fiber converter including alignment pins, according to one or more embodiments shown and described herein; [0061] FIG.7 schematically depicts a front view of a two-dimensional optical interface having an interleaved v-groove array and alignment pins, according to one or more embodiments shown and described herein; [0062] FIG.8 schematically depicts a perspective view of a two-dimensional optical interface having two v-groove arrays separated by a spacer plate, according to one or more embodiments shown and described herein; [0063] FIG. 9A schematically depicts a planar fiber interface, according to one or more embodiments shown and described herein; [0064] FIG.9B schematically depicts a three-row two-dimensional fiber interface, according to one or more embodiments shown and described herein [0065] FIG. 10 is a flow diagram of a process for converting a planar fiber array to a two- dimensional fiber array, according to one or more embodiments shown and described herein; [0066] FIG.11A is a plot of transition height versus transition for an optical fiber of an optical fiber converter, according to one or more embodiments shown and described herein; [0067] FIG.11B is a plot of radius of curvature versus transition length for an optical fiber of an optical fiber converter, according to one or more embodiments shown and described herein; [0068] FIG.12A is a plot of transition height versus transition length for an optical fiber of an optical fiber converter, according to one or more embodiments shown and described herein; [0069] FIG.12B is a plot of radius of curvature versus transition length for an optical fiber of an optical fiber converter, according to one or more embodiments shown and described herein; [0070] FIG. 13A is a plot of minimum radius of curvature versus transition length for optical fibers of an optical fiber converter, according to one or more embodiments shown and described herein; [0071] FIG. 13B is a plot of minimum radius of curvature versus transition length for optical fibers of an optical fiber converter, according to one or more embodiments shown and described herein; [0072] FIG.14A is a plot of bend loss versus wavelength of an optical fiber, according to one or more embodiments shown and described herein; [0073] FIG.14B is a plot of average bend loss versus bend radius of an optical fiber , according to one or more embodiments shown and described herein; [0074] FIG. 15 is a plot of average bend loss versus bend radius of two optical fibers and corresponding exponential fits for each, according to one or more embodiments shown and described herein; [0075] FIG. 16A is a plot of average bend loss versus transition length of four optical fibers, according to one or more embodiments shown and described herein; [0076] FIG. 16B is a plot of average bend loss versus transition length of four optical fibers, according to one or more embodiments shown and described herein; [0077] FIG. 17A is a plot of average bend loss versus transition length of four optical fibers, according to one or more embodiments shown and described herein; [0078] FIG. 17B is a plot of average bend loss versus transition length of four optical fibers, according to one or more embodiments shown and described herein; [0079] FIG. 18A is a plot of average bend loss versus transition length of an optical fiber, according to one or more embodiments shown and described herein; [0080] FIG. 18B is a plot of average bend loss versus transition length of an optical fiber , according to one or more embodiments shown and described herein; [0081] FIG. 19A is a plot of average bend loss versus transition length of an optical fiber, according to one or more embodiments shown and described herein; [0082] FIG. 19B is a plot of average bend loss versus transition length of an optical fiber, according to one or more embodiments shown and described herein; [0083] FIG. 20A is a plot of instantaneous failure probability versus time of an optical fiber, according to one or more embodiments shown and described herein; [0084] FIG.20B is a plot of failure probability versus time of an optical fiber, according to one or more embodiments shown and described herein; [0085] FIG. 20C is a plot of instantaneous failure probability versus time of an optical fiber, according to one or more embodiments shown and described herein; [0086] FIG.20D is a plot of failure probability versus time of an optical fiber, according to one or more embodiments shown and described herein; [0087] FIG.21A is a plot of predicted failure probability versus transition distance of an optical fiber, according to one or more embodiments shown and described herein; [0088] FIG.21B is a plot of predicted failure probability versus transition distance of an optical fiber, according to one or more embodiments shown and described herein; [0089] FIG.22A is a plot of predicted failure probability versus transition distance of an optical fiber, according to one or more embodiments shown and described herein; [0090] FIG.22B is a plot of predicted failure probability versus transition distance of an optical fiber, according to one or more embodiments shown and described herein; [0091] FIG.23A is a plot of predicted failure probability versus transition distance for 16 optical fibers, according to one or more embodiments shown and described herein; [0092] FIG.23B is a plot of predicted failure probability versus transition distance for 16 optical fibers, according to one or more embodiments shown and described herein; [0093] FIG.24A is a plot of predicted failure probability versus transition distance for 16 optical fibers, as described by the Logistic Function, according to one or more embodiments shown and described herein; [0094] FIG.24B is a plot of predicted failure probability versus transition distance for 16 optical fibers, as described by the Error Function, according to one or more embodiments shown and described herein; [0095] FIG.25A is a plot of predicted failure probability versus transition distance for 32 optical fibers, according to one or more embodiments shown and described herein; [0096] FIG.25B is a plot of predicted failure probability versus transition for 32 optical fibers, according to one or more embodiments shown and described herein; [0097] FIG.26A is a plot of predicted failure probability versus transition distance for 32 optical fibers, according to one or more embodiments shown and described herein; and [0098] FIG.26B is a plot of predicted failure probability versus transition distance for 32 optical fibers, according to one or more embodiments shown and described herein. DETAILED DESCRIPTION [0099] Reference will now be made in detail to various optical fiber converters that convert a one-dimensional or planar fiber array to a two-dimensional fiber array. Specifically, the optical fiber converters disclosed herein include a planar fiber interface defining a single row of openings configured to receive a plurality of optical fibers and a two-dimensional fiber interface spaced from the planar fiber interface by a spacing and defining at least a first row of openings and a second row of openings configured to receive the plurality of optical fibers from the planar fiber interface. When assembled with the plurality of optical fibers a first portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the first row of openings of the two-dimensional fiber interface and a second portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the second row of openings of the two-dimensional fiber interface. Optical fiber converters described herein may thereby convert a planar fiber array into a two-dimensional fiber array, which may be necessary for coupling a first optical connector (e.g., a photonic integrated circuit) to a second optical connector (e.g., a multi-fiber push on connector). Further, optical fiber converters described herein may also convert the pitch of a fiber array from a first pitch of a planar fiber array into a second pitch of a two-dimensional fiber array. As will be discussed in greater detail herein, optical fiber converters described herein may have a very small form factor, such as, in embodiments, having a transition width (w) that is less than or equal to about 20 mm. Accordingly, converters such as described herein may not add substantial bulk to an optical assembly and may be used in optical assemblies requiring an optical converter with a very small form factor. In embodiments, the planar fiber interface and the two-dimensional fiber interface may be mechanically decoupled from one another, as described in greater detail below. Mechanical decouplings of the planar fiber interface and the two-dimensional fiber interface may prevent or dampen forces transferred between optical elements, thereby providing greater longevity to components. Various embodiments of optical fiber converters and methods of converting a planar fiber array to a two-dimensional fiber array will be described herein with specific reference to the appended drawings. [00100] Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. [00101] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation. [00102] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification. [00103] As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. [00104] The terms “fiber” and “optical fiber,” as described herein with respect to optical fiber connectors, converters, or other optical assemblies, refer to transparent materials (comprising, e.g., glass or plastic) used in optical communication which transmit information via pulses of light along a length of the material. The terms “fiber” and “optical fiber” may be used interchangeably herein. [00105] The terms “one-dimensional fiber array” and a “planar fiber array,” as described herein with respect to optical fiber converters, refer to optical fiber arrays comprising a single row substantially aligned along a singular axis (i.e., wherein all optical fibers of the fiber array traverse a single plane). The terms “one-dimensional fiber array” and “planar fiber array” may be used interchangeably herein. The positioning of fibers of a one-dimensional fiber array or a planar fiber array relative to each other may be described using a one-coordinate scheme (e.g., an x-value of a position of each fiber relative to, e.g., one lateral surface of an optical interface housing the fiber array). The term “two-dimensional fiber array,” as described herein with respect to optical fiber converters, refers to an optical fiber array comprising a plurality of rows. As such, the positioning of fibers of a two-dimensional fiber array relative to each other may be described using a two- coordinate scheme (e.g., an x- and y-value of a position of each fiber relative to, e.g., a left-hand surface and a bottom surface, respectively, of a face of a fiber interface housing the fiber array). [00106] A “row” of fibers in a fiber array, as described herein with respect to optical fiber converters, refers to a set of optical fibers of a plurality of optical fibers of the optical fiber converter (which may include some or all optical fibers of a plurality of optical fibers of the optical fiber converter) which all share a common lateral axis (e.g., all having a common y-value defining a position of each fiber relative to, e.g., a bottom surface of a face of a fiber interface housing the fiber array). In a planar fiber array, the set of fibers may include all of the fibers of the fiber array. In a two-dimensional fiber array, there may be multiple rows of fibers (and thereby, multiple distinct subsets of fibers, each subset defining a respective row). In embodiments, a two- dimensional fiber array may include two or more rows of fibers, such as three or more, four or more, etc. [00107] The terms “pitch” and “fiber pitch,” as used herein, refer to the distance between center points of each fiber relative to neighboring fibers of the same row. Accordingly, when fibers are housed within openings of an interface, since positions of the openings define positions of the fibers, the pitch of such fibers is thereby determined or estimated by the spacing of such openings relative to each other. [00108] The term “fiber interface,” as described herein, refers to the physical body used to house a fiber array and which couples to an external optical component. As such, in embodiments, a fiber interface may be a “planar fiber interface” or a “one-dimensional fiber interface,” wherein a fiber array housed by the fiber interface is a one-dimensional array having only a single row of fibers. Similarly, in embodiments, a fiber interface may be a two-dimensional fiber interface, wherein a fiber array housed by the fiber interface is a two-dimensional array having a plurality of rows of fibers. [00109] Referring now to FIG.1A, an optical fiber converter 100 is generally illustrated including a planar fiber interface 110 and a two-dimensional fiber interface 120 spaced from the planar fiber interface 110 by a spacing 140. A plurality of optical fibers 130 are illustrated as extending across the spacing 140 from the planar fiber interface 110 and into the two-dimensional fiber interface 120. In the embodiment of FIG.1A, the plurality of fibers 130 may include any number of fibers, such as 12 fibers, 16 fibers, 24 fibers, 36 fibers, etc. In embodiments, the plurality of fibers 130 may include any suitable optical fibers, including fibers having small form factors, such as reduced cladding diameter fibers (“RCFs”), small diameter fibers, stripped fibers, or other fibers, as is described in further detail below. In embodiments, the plurality of fibers 130 may include single mode fibers (e.g., single-mode fibers with cable cutoff wavelengths less than 1260 nm, single- mode fibers with fiber cutoff wavelengths less than 1260 nm, or the like), cutoff-shifted fibers with cable cutoff wavelengths less than 1520 nm, non-zero dispersion-shifted fibers with zero dispersion wavelengths between 1400 and 1650 nm, multimode fibers, or few mode fibers. In embodiments, the plurality of fibers 130 may include polarization-maintaining fibers or bend insensitive fibers. In embodiments, the plurality of fibers 130 may include multicore fibers (e.g., having two or more cores surrounded by a common cladding) or hollow-core fibers. In embodiments, the plurality of fibers 130 may include dispersion compensating fibers. In embodiments, fibers may have reduced coating diameters such as between about 100 microns and about 200 microns. In embodiments, the plurality of optical fibers 130 may include any types of optical fibers such as any combination of some or all of the above-referenced fiber types, or the like. [00110] As illustrated, the planar fiber interface 110 receives and houses the plurality of fibers 130 as a single row or array, the arrangement of the plurality of fibers 130 within the planar fiber interface 110 being a planar fiber array 132. That is, the planar fiber array 132 is housed within a single row of openings 111 defined by the planar fiber interface 110. In this embodiment, the single row of openings 111 is provided by a v-groove array 112. In other embodiments, and as depicted in FIG.2A, the single row of openings 111 of the planar fiber interface 110 may instead be holes in the planar fiber interface 110. Furthermore, in embodiments, instead of v-grooves, other shaped grooves are contemplated and possible, e.g., u-shaped, square-shaped, etc. The single row of openings 111 may be formed on a top surface 116 of the planar fiber interface 110, a different surface, or formed through a thickness of the planar fiber interface 110 (e.g., as illustrated in FIG.2A). [00111] In embodiments, the planar fiber interface 110 may be formed of any suitable material, such as, but not limited to, glass, glass-ceramic, polymer, etc. When formed of glass, the material may be CTE (coefficient of thermal expansion) matched to silicon, which may minimize thermal dependent losses between fibers the silicon waveguides, where present. In embodiments, a lid (depicted in FIGS. 5-6 and described below) may be positioned over the top surface 116 of the planar fiber interface 110, so as to extend over the single row of openings 111. In embodiments, the lid may be formed of the same material as the planar fiber interface 110 or a different material. In embodiments, the planar fiber interface 110 may be formed via any suitable technique such as by injection molding, machining, or the like. In some embodiments, the planar fiber interface 110 may etched to form the single row of openings 111. In other embodiments, the openings may be machined. [00112] In embodiments, the plurality of fibers 130 may be attached to the planar fiber interface 110 within the single row of openings 111 by an adhesive. In embodiments, the adhesive may be a thermally stable adhesive. In embodiments, the adhesive may be a heat-curing adhesive (for example, the EPO-TEK® 353ND adhesive). In embodiments, the adhesive may be a UV-curing adhesive. In embodiments, the adhesive may be a heat- and UV-curing adhesive. In embodiments comprising a lid, the lid may be similarly affixed to the top surface 116 or to another surface of the planar fiber interface 110 with the adhesive or a different adhesive. [00113] Still referring to FIG.1A, the two-dimensional fiber interface 120 may similarly house the plurality of fibers 130 but in multiple rows, such as two or more rows. For example, the two- dimensional fiber interface 120 has at least a first row of openings 122 and a second row of openings 124, and each of the rows of openings 122, 124 may include a plurality of openings. The rows of openings 122, 124 receive the plurality of fibers 130 from the single row of openings 111 of the planar fiber interface 110 and separate the plurality of fibers 130 between the first row of openings 122 and the second row of openings 124, thereby housing the plurality of fibers 130 as a two-dimensional fiber array 134. The first row of openings 122 may be positioned at a first height (as measured in the y-direction of the depicted coordinate axis) and the second plurality of openings 124 may be positioned at a second height (as measured in the y-direction of the depicted coordinate axes) which is different from the first height. Since each of the rows of openings 122, 124 has a substantially constant height (as defined by the y-axis of FIG.1A) while also having a different height with respect to each other, a position of any opening of the rows of openings 122, 124 differs relative to at least some other openings of the rows of openings 122, 124 in two dimensions (i.e., differing in x- and y-position), and so the rows of openings 122, 124 thereby provide a two-dimensional fiber array. [00114] As illustrated in the embodiment of FIG.1A, the rows of openings 122, 124 may be holes formed through a thickness of the two-dimensional fiber interface 120. The holes may have any shape, and need not be round as depicted, but may be square, rectangular, oval-shaped, etc. Moreover, in some embodiments, (as depicted in FIGS. 5-6 and as will be described in greater detail below) some or all of the openings of either or both of the rows of openings 122, 124 may instead be defined by a v-groove array, an interleaved v-groove array, two v-groove arrays and a spacer plate, or any other mechanism which provides a two-dimensional fiber interface having a plurality of rows of openings. It is noted that while the embodiments depicted in FIG. 1A illustrates two rows of openings in the two-dimensional fiber interface 120 (the rows of openings 122, 124), there may be any number of rows of openings greater than one, such as two or more, three or more, four or more, etc. [00115] In embodiments, the two-dimensional fiber interface 120 may be formed via any suitable technique such as by injection molding, machining, or the like. In some embodiments, the two- dimensional fiber interface 120 may etched to form the rows of openings 122, 124. In other embodiments, the openings may be drilled, such as by mechanical drilling, laser drilling, and/or other laser ablation techniques. The two-dimensional fiber interface 120 may be formed of any suitable material and may be the same or a different material from the planar fiber interface 110. In some embodiments, the two-dimensional fiber interface 120 may be an etched glass plate or etched glass-ceramic plate (e.g., chemically etched, precision machine etched, precision etched, laser etched via any laser ablation technologies, or the like). In some embodiments, the two- dimensional fiber interface 120 may be formed of a material which is CTE matched to standard organic ferrule materials to minimize CTE induced losses. Accordingly, the two-dimensional fiber interface 120 may provide an interface for connecting to a ferrule of an optical connector. [00116] In embodiments, the plurality of fibers are routed into the first row of openings 122 or the second row of openings and fixed thereto, such as via an adhesive, such as described above. [00117] In embodiments, the spacing 140 between the planar fiber interface 110 and the two- dimensional fiber interface 120 may be filled with a material 142 to, e.g., encapsulate the fibers of the plurality of fibers 130, provide mechanical protection for the fibers of the plurality of fibers 130, provide environmental protection for the fibers of the plurality of fibers 130, and/or increase reliability of the optical fiber converter 100. In embodiments, portions of the fibers of the fiber plurality of fibers 130 within the spacing 140 may be stripped (e.g., lacking polymer coatings), and so the material 142 may provide protection for such stripped fibers. In embodiments, the material may be an organic material. In embodiments, the material may be an adhesive. In embodiments, the material 142 may be soft, flexible or the like, so as to mechanically decouple the fiber interfaces 110, 120. By mechanically decoupling the fiber interfaces 110, 120, external forces acting on either of the fiber interfaces 110, 120 may be prevented from transmitting to the other of the fiber interfaces 110, 120 or otherwise dampened when transmitting to the other of the fiber interfaces 110, 120. For example, during mating of an optical connector to the two- dimensional fiber interface 120, the planar fiber interface 110 may be insulated from the force acting on the two-dimensional fiber interface 120 via the material 142 between the fiber interfaces 110, 120. [00118] By extending across the spacing 140 from the planar fiber interface 110 and into the two- dimensional fiber interface 120, the plurality of fibers 130 transition from the planar fiber array 132, within the planar fiber interface 110, into the two-dimensional fiber array 134, in the two- dimensional fiber interface 120. By transitioning the plurality of fibers 130 from the planar fiber array 132 into the two-dimensional fiber array 134, the optical fiber converter 100 may convert a pitch of the plurality of fibers 130. For example, in embodiments, the first row of openings 122 of the two-dimensional fiber interface 120 may define a different pitch than a pitch defined by the single row of openings 111 of the planar fiber interface 110. Similarly, in embodiments, the second row of openings 124 of the two-dimensional fiber interface 120 may define a different pitch than a pitch defined by the single row of openings 111 of the defined by the single row of openings 111 of the planar fiber interface 110. In some embodiments, each of the rows of openings 122, 124 of the two-dimensional fiber interface 120 may define a different pitch than a pitch defined by the single row of openings 111 of the planar fiber interface 110. In some embodiments, a pitch defined by the first row of openings 122 may be different than a pitch defined by the second row of openings 124. In embodiments, a pitch defined by the first row of openings 122 may be the same as a pitch defined by the second row of openings 124. In embodiments, such as depicted in FIG. 7 and described below, the first row of openings 122 may be offset, in the x-direction, from the second row of openings 124, such that the first row 122 has differing start and end points, in the x-direction, then start and end points of the second row of openings 124. [00119] Referring to FIG.1B, in embodiments, the planar fiber interface 110 may be configured to couple to a first optical element 102 on an exterior surface 113 of the planar fiber interface 110. In embodiments, the first optical element 102 may comprise a planar fiber array that couples to the planar fiber interface. In embodiments, the first optical element 102 may be a photonic integrated circuit (“PIC”), a fiber array unit (“FAU”), or the like. In embodiments, the exterior surface 113 of the planar fiber interface 110, e.g., facing the first optical element 102, may be flat polished and/or have coatings applied thereto (e.g., an anti-reflective coating such as those described above). In embodiments, the coatings may include single- or multi-layer thin film filters. In embodiments, the exterior surface 113 of the planar fiber interface 110 may include additional coupling elements, and, in embodiments, the additional coupling elements may enable the planar fiber interface 110 to couple to the first optical element 102 and/or improve the quality of the coupling of the planar fiber interface 110 to the first optical element 102. In embodiments, the additional coupling elements may include a micro-lens array, wherein each fiber of the planar fiber array 132 terminates at, before, or beyond the exterior surface 113 with a micro-lens. In embodiments, the additional coupling elements may include vertical grating couplers, wherein each fiber of the planar fiber array 132 terminates at, before, or beyond the exterior surface 113 with a vertical grating coupler, and, in certain such embodiments, the vertical grating couplers may enable vertical coupling between the first optical element 102 and the planar fiber interface 110. In embodiments, the additional coupling elements may include edge couplers, wherein each fiber of the planar fiber array 132 terminates at, before, or beyond the exterior surface 113 with an edge coupler, and, in certain such embodiments, the edge couplers may enable edge coupling between the first optical element 102 and the planar fiber interface 110. In embodiments comprising additional coupling elements, the additional coupling elements may enable the planar fiber interface 110 to directly attach to the first optical element 102. In embodiments, the additional coupling elements may enable the planar fiber interface 110 to provide low loss alignment with the first optical element 102 using micro lenses. In embodiments, a pitch defined by the first row of openings 111 may depend on a pitch of the first optical element 102. For example, in embodiments, a pitch defined by the first row of openings 111 may depend on a pitch of waveguides of the first optical element 102. [00120] Still referring to FIG.1B, in embodiments, the two-dimensional fiber interface 120 may be configured to couple to a second optical element 104 on an exterior surface 125 of the two- dimensional fiber interface 120. In embodiments, the second optical element 104 may house a two-dimensional fiber array. In embodiments, the second optical element 104 may be a multi- fiber push on (“MPO”) connector. In embodiments, the second optical element 104 may be an MXC® connector. In embodiments, the exterior surface 125 of the two-dimensional fiber interface 120 may be flat polished, and, in embodiments, the flat polish of the exterior surface 125 may reduce return loss of the optical fiber converter 100. In embodiments, the exterior surface 125 of the two-dimensional fiber interface 120 may be angle polished, and, in embodiments, the angle polish of the exterior surface 125 may reduce return loss of the optical fiber converter 100. In embodiments, the exterior surface 125 may comprise an anti-reflective coating, such as the anti- reflective coatings described above. In embodiments, the exterior surface 125 of the two- dimensional fiber interface 120 may include additional coupling elements, and, in embodiments, the additional coupling elements may enable the two-dimensional fiber interface 120 to couple to the second optical element 104 and/or improve the quality of the coupling of the two-dimensional fiber interface 120 to the second optical element 104. In embodiments, the additional coupling elements may include a micro-lens array, wherein each fiber of the two-dimensional fiber array 134 terminates at, before, or beyond the exterior surface 125 with a micro-lens. In embodiments, the additional coupling elements may include vertical grating couplers, wherein each fiber of the two-dimensional fiber array 134 terminates at, before, or beyond the exterior surface 125 with a vertical grating coupler, and, in certain such embodiments, the vertical grating couplers may enable vertical grating coupling between the second optical element 104 and the two-dimensional fiber interface 120. In embodiments, the additional coupling elements may include edge couplers, wherein each fiber of the two-dimensional fiber array 134 terminates at, before, or beyond the exterior surface 125 with an edge coupler, and, in certain such embodiments, the edge couplers may enable edge coupling between the second optical element 104 and the two-dimensional fiber interface 120. In embodiments comprising additional coupling elements, the additional coupling elements may enable the two-dimensional fiber interface 120 to directly attach to the second optical element 104. In embodiments, the additional coupling elements may enable the two- dimensional fiber interface 120 to provide low loss alignment with the second optical element 104 using micro lenses. In embodiments, a pitch defined by either or both of the rows of openings 122, 124 may depend on a pitch of the second optical element 104. For example, in embodiments, a pitch defined by either or both of the rows of openings 122, 124 may depend on a pitch of waveguides of the second optical element 104. [00121] Accordingly, the optical fiber converter 100 may connect the first optical element 102 to the second optical element 104, and, in embodiments, the optical fiber converter 100 may convert the planar fiber array 132 into the two-dimensional fiber array 134 to enable the optical fiber converter 100 to optically couple the first optical element 102 to the second optical element 104 using the plurality of fibers 130. However, as described above, certain contexts may require that the optical fiber converter 100 be very small. [00122] In embodiments wherein the spacing 140 is filled with the material 142, the material 142 may mechanically decouple the first optical element 102 and the second optical element 104 by, e.g., being a flexible material. Accordingly, in such embodiments, external forces acting on either of the optical elements 102, 104 may be prevented from transmitting to the other of the optical elements 102, 104 or otherwise dampened when transmitted to the other of the optical elements 102, 104. [00123] Referring again to FIG.1A, in embodiments, a transition width (w) is the distance a fiber of the plurality of fibers 130 must extend across, through the spacing 140, to extend from the planar fiber interface 110 to the two-dimensional fiber interface 120. Accordingly, the transition width (w) is defined by a size of the spacing 140. In embodiments, the transition width (w) may be less than or equal to 20 mm. The transition width (w) defines a minimum length of a portion of each fiber of the plurality of fibers 130 that may extend from the planar fiber interface 110 to the two- dimensional fiber interface 120 (a length of a portion of a fiber within the spacing 140 and extending from the planar fiber interface 110 into the two-dimensional fiber interface 120 being a “transition length” of the fiber). However, to convert the plurality of fibers 130 from the planar fiber array 132 into the two-dimensional fiber array 134, at least some of the fibers of the plurality of fibers 130 may bend in either or both of the x- and y-direction to accommodate differences in height (as measured in the y-direction) and/or differences (as measured in the x-direction) between openings of the v-groove array 112 and corresponding openings of either or both of the first row of openings 122 and/or the second row of openings 124. Accordingly, the length of a portion of any fiber of the plurality of fibers 130 within the spacing 140 may be greater than the transition width (w) when that fiber moves in the x- and/or y-direction when extending from the planar fiber interface 110 and into the two-dimensional fiber interface 120. In embodiments wherein a pitch defined by the single row of openings 111 and a pitch defined by either or both of the rows of openings 122, 124 differ (as described in further detail below), some or all fibers of the plurality of fibers 130 may not move in the x-direction when extending across the spacing 140, and, in such embodiments, such fibers may only move in the y-direction when extending across the spacing 140. [00124] Fibers of the plurality of fibers 130 will bend more as (1) differences in position between a position of the fiber in the planar fiber interface 110 and a position of the fiber in the two- dimensional fiber interface 120 (as measured in the x-y plane; the distance in the x-y plane a fiber travels between the fiber interfaces 110, 120 being a “planar transition distance”); (2) fiber cladding diameter (as described in further detail below) increases; and/or (3) as the transition width (w) decreases. By bending, fibers of the plurality of fibers 130 may incur propagation loss within the spacing 140, and, the more a fiber bends (e.g., leading to a smaller bend radius), the more propagation loss may be incurred. Propagation loss of fibers of the plurality of fibers 130 within the spacing 140 may thereby be reduced by (1) decreasing the planar transition distance of fibers of the plurality of fibers 130, (2) increasing the transition width (w), (3) increasing fiber bend radius, and/or (4) by using low macrobend loss fibers, as is described below. [00125] Depending on a desired context of use, the optical fiber converter 100 may have a maximum propagation loss threshold that, if exceeded, may provide sub-optimal or unusable levels of propagation loss for the desired context of the optical fiber converter 100. In embodiments, a maximum propagation loss threshold of the optical fiber converter 100 may be 0.2 dB, though, in other embodiments, other maximum propagation loss thresholds are contemplated and possible and, in such embodiments, a maximum propagation loss threshold may depend upon a context of use of the optical fiber converter 100. Propagation loss of an optical fiber may be a function of, at least in part, a bend radius of the optical fiber (e.g., within the spacing 140) and a macrobend loss of the optical fiber (measured in, e.g., dB/turn). A macrobend loss of the optical fiber may depend upon, e.g., a material of the optical fiber. For example, in embodiments, an optical fiber of the optical fiber converter 100 may have a macrobend loss, at a transmission wavelength of 1550 nm, of less than 0.5 dB/turn at a bend radius of 15 mm, or less than 0.5 dB/turn at a bend radius of 10 mm, or less than 0.5 dB/turn at a bend radius of 5 mm, or even less than 0.5 dB/turn at a bend radius of 3 mm. In some embodiments, an optical fiber of the optical fiber converter 100 may have a macrobend loss, at a transmission wavelength of 1310 nm, of less than 0.5 dB/turn at a bend radius of 15 mm, or less than 0.5 dB/turn at a bend radius of 10 mm, or less than 0.1 dB/turn at a bend radius of 5 mm, or even less than 0.5 dB/turn at a bend radius of 3 mm. [00126] Fibers of a given diameter and macrobend loss in an optical fiber converter of a given transition width (w) in a context with a given maximum propagation loss threshold, such fibers will have a maximum pitch conversion (i.e., a difference in pitches between a pitch defined by the single row of openings 111 and a pitch defined by either or both of the rows of openings 122, 124) which, if exceeded, will cause the maximum propagation loss threshold to also be exceeded. However, as described above, contexts may desire optical fiber converters which are very small. By decreasing the size of the optical fiber converter 100, the transition width (w) will also be decreased, thereby limiting the maximum pitch conversion of fibers of the plurality of fibers 130. Nonetheless, a greater maximum pitch conversion of fibers of the plurality of fibers 130 enables a greater range of pitch conversion between the planar fiber array 132 and the two-dimensional fiber array 134 in addition to a greater range of height differences between rows of the two-dimensional fiber array 134 (e.g., the rows of openings 122, 124) and the single row of openings 111 (e.g., to allow for a greater row height, as described below with respect to FIG.2B, or to allow for a greater number of rows in the two-dimensional fiber array 134). Accordingly, for a context with a given maximum propagation loss threshold, there is a desire to both minimize the transition width (w) of the optical fiber converter 100 while also maximizing the maximum pitch conversion of fibers of the plurality of fibers 130. [00127] Increasing a fiber bend radius of fibers of the plurality of fibers 130 may reduce propagation loss of fibers of the plurality of fibers 130 within the spacing 140. Reducing a cladding diameter of fibers of the plurality of fibers 130 (a “cladding diameter” being the diameter of a fiber as measured from an exterior surface of a cladding of the fiber) may allow for smaller fiber bend radii of such fibers of the plurality of fibers 130 within the spacing 140, as a thinner fiber will tighter bending than a thicker fiber to transition the planar transition distance. Reducing the cladding diameter may thereby enable a larger maximum pitch conversion, a larger maximum height difference between rows of the two-dimensional fiber array 134, and/or a lower minimum transition width (w). Further, reducing the cladding diameter may also lower a minimum possible pitch obtainable by the planar fiber array 132 and/or by the two-dimensional fiber array 134, as, by using smaller fibers, such fibers of the planar fiber array 132 and/or of the two-dimensional fiber array 134 may be placed closer together (i.e., decreasing pitch of such fiber arrays). Reducing the cladding diameter may thereby also allow for reduced distances between openings of any, each, or all of the single row of openings 111, the first row of openings 122, and/or the second row of openings 124, as the rows of openings 111, 122, 124 each define a pitch of a fiber array housed therein. Accordingly, using fibers having a reduced cladding diameter increase the maximum pitch conversion of fibers of the plurality of fibers 130, increase the height difference between rows of the two-dimensional fiber array 134, reduce the minimum possible pitch of the planar fiber array 132 and/or the two-dimensional fiber array 134, and/or reduce the minimum possible transition width (w) of the optical fiber converter 100. [00128] In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be less than or equal to 125 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be less than or equal to 100 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be less than or equal to 80 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may even be less than or equal to 62.5 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be greater than or equal to 50 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be greater than or equal to 50 ^m and less than or equal to 125 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be greater than or equal to 50 ^m and less than or equal to 100 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be greater than or equal to 50 ^m and less than or equal to 80 ^m. In embodiments, a cladding diameter of fibers of the plurality of fibers 130 may be greater than or equal to 50 ^m and less than or equal to 62.5 ^m. Certain fibers having such diameters are described in U.S. Pat. No.11,181,687 (“Small Diameter Low Attenuation Optical Fiber”), U.S. Pat. No.11,187,853 (“Small Outer Diameter Low Attenuation Optical Fiber”), and U.S. Pat. No. 11,181,686 (“Small Diameter Low Attenuation Optical Fiber”), each of which are incorporated by reference herein in their entireties. [00129] In embodiments , any, some, or all of the plurality of fibers 130 may have a coating (e.g., a polymer coating, acrylate coatings, non-acrylate coatings, etc.) applied to an external surface of a cladding of the fiber. In such embodiments, the coating of the plurality of fibers 130 may cause the fiber to have a “coated diameter” in excess of the fiber’s cladding diameter. Accordingly, a “coated diameter” is the diameter of a fiber as measured from an exterior surface of a coating of the fiber. In embodiments, a coated diameter of fibers of the plurality of fibers 130 may be less than or equal to 250 ^m. In embodiments, a coated diameter of fibers of the plurality of fibers 130 may be less than or equal to 200 ^m. In embodiments, a coated diameter of fibers of the plurality of fibers 130 may be less than or equal to 190 ^m. In embodiments, a coated diameter of fibers of the plurality of fibers 130 may be less than or equal to 180 ^m. In embodiments, a coated diameter of fibers of the plurality of fibers 130 may be less than or equal to 165 ^m. In embodiments, a coated diameter of fibers of the plurality of fibers 130 may be less than or equal to 145 ^m. In embodiments, a coated diameter of the plurality of fibers 130 may even be less than or equal to 125 ^m. [00130] In embodiments, fibers of the fiber array 130, as described above, may be RCFs. In such embodiments, RCFs may have a mode field diameter that is comparable to that of a single mode fiber (“SMF”). In certain such embodiments, the mode field diameter of the RCF may be, at a wavelength of 1310 nm, greater than or equal to 8.6 microns and less than or equal to 9.5 microns. Such embodiments may enable the optical fiber converter 100 to experience lower coupling loss than other waveguides, such as bulk glass laser written waveguides. [00131] In embodiments, such as embodiments wherein the spacing 140 is filled with the material 142, fibers of the fiber array 130 may lack acrylate coating (due to, e.g., being stripped). Accordingly, in such embodiments, fibers of the fiber array 130 may be solder reflow compatible due to, e.g., the absence of acrylate coatings on the fibers. [00132] Additionally, using fibers with a lower macrobend loss enables greater bending of such fibers without exceeding potential maximum propagation loss thresholds, as lower macrobend loss fibers can bend to a smaller radius than higher macrobend loss fibers while suffering the same amount of bend loss. By enabling a smaller bend radius, greater planar transition distances and greater differences in pitch between the planar fiber array 132 and rows of the two-dimensional fiber array 134 and greater maximum transition distances of fibers of the plurality of fibers 130 may be obtained. Additionally, by enabling a smaller bend radius, smaller transition widths (w) of the optical fiber converter 100 may be used. Accordingly, in embodiments, each optical fiber of the plurality of fibers 130 may have a macrobend loss, at a transmission wavelength of 1550 nm, that is less than or equal to 0.5 dB, or less than or equal to 0.2 dB, or even less than or equal to 0.1 dB. In some embodiments, each optical fiber of the plurality of fibers 130 may have a macrobend loss, at a transmission wavelength of 1310 nm, that is less than or equal to 0.5 dB, or less than or equal to 0.2 dB, or even less than or equal to 0.1 dB. [00133] Referring now to FIG. 2A, the planar fiber interface 110 houses the planar fiber array 132. In the embodiment of FIG.2A, as opposed to the embodiment of FIG.1A, the openings of the single row of openings 111 are holes 115 in the planar fiber interface 110, rather than being the v-groove array 112. The single row of openings 111 is aligned along an axis 112A (in this embodiment, the x-axis). In the embodiment of FIG.2A, the axis 112A is substantially parallel to each of the top surface 116 and a bottom surface 117 of the planar fiber interface 110. However, in other embodiments, an axis of the single row of openings 111 may not be parallel relative to either or both of the top surface 116 and the bottom surface 117. In the embodiment of FIG.2A, the axis 112A is substantially perpendicular to each of lateral surfaces 118 of the planar fiber interface 110. However, in other embodiments, an axis of the single row of openings 111 may not be perpendicular relative to either or both of the lateral surfaces 118 of the planar fiber interface 110. The planar fiber array 132 comprises a first pitch (p₁), wherein the first pitch (p₁) is defined by the spacing of the openings of the single row of openings 111 in the x-direction of the depicted coordinate axes. [00134] Referring now to FIG. 2B, the two-dimensional fiber interface 120 houses, within the rows of openings 122, 124, the two-dimensional fiber array 134. Each of the rows of openings 122, 124 are aligned along a respective axis (a first axis 122A and a second axis 124A, respectively) parallel to the x-axis. Each axis runs through centers of each of the openings of a respective one of the rows of openings 122, 124. In the embodiment of FIG. 2B, the first axis 122A is substantially parallel to the second axis 124A. However, in other embodiments, an axis of the first row of openings 122 may not be parallel to an axis of the second row of openings 124. In the embodiment of FIG.2B, each of the axes 122A, 124A are substantially parallel to each of base surfaces 127 of the two-dimensional fiber interface 120. However, in other embodiments, an axis of the first row of openings 122 and/or an axis of the second row of openings 124 may not be parallel to either or both of the base surfaces 127. In the embodiment of FIG.2B, each of the axes 122A, 124A are substantially perpendicular to each of lateral surfaces 128 of the two-dimensional fiber interface 120. However, in other embodiments, an axis of the first row of openings 122 and/or an axis of the second row of openings 124 may not be perpendicular to either or both of the lateral surfaces 128. [00135] The two-dimensional fiber array 134 has a second pitch (p2), wherein the second pitch (p₂) is defined by the spacing of the openings of the first row of openings 122 in the x-direction of the depicted coordinate axes, and a third pitch (p₃), wherein the third pitch (p₃) is defined by the spacing of the openings of the second row of openings 124 in the x-direction of the depicted coordinate axes. In embodiments, the second pitch (p2) and the third pitch (p3) may be equal. In embodiments, the second pitch (p₂) and the third pitch (p₃) may not be equal. In embodiments, the first pitch (p1) of the planar fiber array 132 and the second pitch (p2) may be equal. In embodiments, the first pitch (p1) and the third pitch (p3) may be equal. In embodiments, the first pitch (p₁), the second pitch (p₂), and the third pitch (p₃) may be equal. In embodiments, the first pitch (p₁) and the second pitch (p₂) may not be equal. In embodiments, the first pitch (p₁) and the third pitch (p3) may not be equal. In embodiments, the first pitch (p1), the second pitch (p2), and the third pitch (p₃) may not be equal. In embodiments, the first pitch (p₁) may be less than or equal 550 ^m, such as less than or equal to 500 ^m, less than or equal to 300 ^m, less than or equal to 250 ^m, less than or equal to 200 ^m, less than or equal to 165 ^m, less than or equal to 150 ^m, less than or equal to 127 ^m, less than or equal 100 ^m, or even less than or equal 84 ^m. In embodiments, the second pitch (p₂) may be less than or equal to 550 ^m, such as less than or equal to 500 ^m, less than or equal to 300 ^m, less than or equal to 200 ^m, less than or equal to 250 ^m, less than or equal to 165 ^m, less than or equal to 150 ^m, less than or equal to 127 ^m, less than or equal to 100 ^m, or even less than or equal to 84 ^m. In embodiments, the third pitch (p₃) may be less than or equal to 550 ^m, less than or equal to 500 ^m, less than or equal to 300 ^m, less than or equal to 250 ^m, less than or equal to 200 ^m, less than or equal to 165 ^m, less than or equal to 150 ^m, less than or equal to 127 ^m, than or equal to 100 ^m, or even less than or equal to 84 ^m. Other ranges are contemplated and possible. [00136] Still referring to FIG.2B, the rows of openings 122, 124 are separated by a row height (h_r) (as measured from each of the axes 122A, 124A). In the embodiment of FIG.2B, each of the rows of openings 122, 124 are offset from the x-axis by +0.5h and -0.5h, respectively, in the y- direction, and so, since the axis 112A is aligned with the x-axis, the rows of openings 122, 124 are similarly offset from the planar fiber array 132 by +0.5h and -0.5h, respectively, in the y-direction. Accordingly, each fiber of the plurality of fibers 130, when extending across the spacing 140, may each move +/-0.5h in the y-direction to extend from the respective opening of the fiber in the planar fiber interface 110 to the fiber’s respective opening in the two-dimensional fiber interface 120. However, as is described in further detail below with reference to FIG.6, in certain embodiments the rows of openings 122, 124 may be centered about an axis other than the axis 112A. Accordingly, in such embodiments, fibers of the plurality of fibers 130 that extend into the first row of openings 122 move a different distance in the y-direction when extending across the spacing 140 than fibers of the plurality of fibers 130 that extend into the second row of openings 124 when extending across the spacing 140. [00137] In embodiments, the row height (hr) may be less than or equal to 1 mm, such as less than or equal to 0.25 mm, such as less than or equal to 0.127 mm, such as less than or equal to 0.125 mm, such as less than or equal to 0.1 mm, etc. In embodiments, the row height (h_r) may be greater than or equal to 0.05 mm, such as greater than or equal to 0.1 mm, such as greater than or equal to 0.125 mm, such as greater than or equal to 0.127 mm, such as greater than or equal to 0.25 mm, etc. In embodiments, the row height (h_r) may be less than or equal to 1 mm and greater than or equal to 0.05 mm. In embodiments, the row height (h_r) may be between 1 mm and 0.1 mm, such as between 1 mm and greater than or equal to 0.125 mm. In embodiments, the row height (hr) may be less than or equal to 1 mm and greater than or equal to 0.127 mm. In embodiments, the row height (h_r) may be less than or equal to 1 mm and greater than or equal to 0.25 mm. In embodiments, the row height (hr) may be less than or equal to 0.25 mm and greater than or equal to 0.05 mm. In embodiments, the row height (hr) may be less than or equal to 0.25 mm and greater than or equal to 0.1 mm. In embodiments, the row height (h_r) may be less than or equal to 0.25 mm and greater than or equal to 0.125 mm. In embodiments, the row height (h_r) may be less than or equal to 0.25 mm and greater than or equal to 0.127 mm. In embodiments, the row height (hr) may be less than or equal to 0.127 mm and greater than or equal to 0.05 mm. In embodiments, the row height (h_r) may be less than or equal to 0.127 mm and greater than or equal to 0.1 mm. In embodiments, the row height (hr) may be less than or equal to 0.127 mm and greater than or equal to 0.125 mm. In embodiments, the row height (h_r) may be less than or equal to 0.125 mm and greater than or equal to 0.05 mm. In embodiments, the row height (h_r) may be less than or equal to 0.125 mm and greater than or equal to 0.1 mm. In embodiments, the row height (hr) may be less than or equal to 0.1 mm and greater than or equal to 0.05 mm. [00138] The planar fiber array 132 has a row width (R_w3) that is greater than a row width (R_w4) of the two-dimensional fiber array 134. Accordingly, in the embodiment of FIGS.2A-2B, some fibers of the plurality of fibers 130, when extending across the spacing 140, may require greater movement in the x-direction than fibers of the embodiment of FIG.1A. Referring again to FIG. 1A for comparison, the v-groove array 112 defines a row width (R_w1) and each of the rows of openings 122, 124 define a row width (Rw2). In the embodiment of FIG.1A, the row widths (Rw1) and (Rw2) are equal, and so fibers of the plurality of fibers 130, when extending across the spacing 140, move only slightly in the x-direction, if at all. [00139] Referring now to FIG.3, a fiber 300 is shown extending across the spacing 140 from the planar fiber interface 110 and into the two-dimensional fiber interface 120. Due to the movement of the fiber 300 in the y-direction by 0.5h, the fiber 300 has, within the spacing 140, a sigmoidal shape (or s-bend). The fiber may have a similar shape in the X-Z plane. [00140] The sigmoidal shape of the fiber 300 (and, in embodiments, of any fiber of the plurality of fibers 130) within the spacing 140 may be represented, in the y-direction, by, in some embodiments, the Logistic Function:

[00141] The value “z” is the position of the fiber 300 in the z-direction within the spacing 140, with a minimum value of z = -0.5w (w being the transition width (w) of the spacing 140), at the interior surface 114 of the planar fiber interface 110, and a maximum value of z = +0.5w, at the interior surface 126 of the two-dimensional fiber interface 120). The value “l0” is a length scaling parameter describing the sharpness of the S-shaped curve, and l₀ may be determined by measuring, for a given dimensions w and h, an actual fiber length of the portion of the fiber 300 within the spacing 140. In this representation of the Logistic Function, the function is centered at y = 0, with minimum and maximum y-values of -0.5h (e.g., a height, in the y-direction, of the fiber 300 at the interior surface 114 of the planar fiber interface 110, where z = -0.5w) and +0.5h (e.g., a height, in the y-direction, of the fiber 300 at the interior surface 126 of the two-dimensional fiber interface 120, where z = +0.5w), respectively. The value “h” is thereby the transition height of the fiber 300 when extending from the planar fiber interface 110 and into the two-dimensional fiber interface 120 across the spacing 140 (e.g., the difference between the y-value of the position of the fiber at z = -0.5w and the y-value of the position of the fiber at z = +0.5w). [00142] In the embodiment of FIGS.2A-3, an absolute value of the transition height (h) will be equal to one half of the row height (hr), as shown in FIG.3, since, in this embodiment, the planar fiber array 132 is positioned directly in the middle, in the y-direction, of the rows of openings 122, 124 (as each of the axes 122A, 124A are an equal distance from the axis 112A). Accordingly, in that embodiment, for fibers extending into the two-dimensional fiber interface 120, first row of openings 122 and the second row of openings 124, the transition height (h) of each fiber of the plurality of fibers 130 will be either +0.5hr (for fibers extending into the first row of openings 122) or -0.5hr (for fibers extending into the second row of openings 124). However, in other embodiments wherein the planar fiber array 132 is not positioned directly in the middle, in the y- direction, of the rows of openings 122, 124, an absolute value of a transition height of fibers extending into the first row of openings 122 may not be equal to a transition height of fibers extending into the second row of openings 124. [00143] The Logistic Function may alternatively be centered with minimum and maximum y- values of 0 and h, in which case the Logistic Function instead takes the following form:

[00144] Both forms of the Logistic Function (i.e., equations (1) and (2)) yield the same sigmoidal form, and each of equations (1) and (2) merely differ with regard to defining where y = 0 (in equation (1), at z = 0; in equation (2), at z = -0.5w). [00145] However, the Logistic Function is only one possible representation of the sigmoidal shape of the fiber 300 in the spacing 140. In other embodiments, the sigmoidal shape of the any fiber of the plurality of fibers 300 in the spacing 140 may be described, in some embodiments, by the Error Function, which takes the following form: ^^{ൌ ^} ଶ ^erf

[00146] In the Error Function, as in the Logistic Function, the value “h” is the transition height of the fiber 300, and the value “z” is the position of the fiber 300 in the spacing 140, with a minimum value of z = -0.5w (w being the transition width (w) of the spacing 140), at the interior surface 114 of the planar fiber interface 110, and a maximum value of z = +0.5w, at the interior surface 126 of the two-dimensional fiber interface 120. The value “l1” is a length scaling parameter describing the sharpness of the S-shaped curve, and l1 may be determined by measuring, for a given dimensions w and h, an actual fiber length of the portion of the fiber 300 within the spacing 140. [00147] The Logistic Function (i.e., equations (1) and (2)) and the Error Function (i.e., equation (3)) each provide differing descriptions of the sigmoidal shape of the fiber 300 in the spacing 140 (including, e.g., a described length of the portion of the fiber 300 within the spacing 140). Depending on contextual factors such as, e.g., fiber material properties of the fiber 300 and/or properties of the connection and coupling of the fiber 300 to either or both of the planar fiber interface 110 and the two-dimensional fiber interface 120 (such as an adhesive used for attaching the fiber 300 to either or both of the fiber interfaces 110, 120), one of the Logistic Function or the Error Function may provide a more accurate representation of the sigmoidal shape of the fiber 300, as described below and depicted in FIGS.11A-12B. [00148] For each of the Logistic Function and the Error Function, an instantaneous radius of curvature in the y-direction (^y) may be described by:

[00149] In equation (4), y’ and y” are the first and second derivatives of either of the Logistic Function (equations (1) or (2)) or the Error Function (equation (3)) with respect to z. [00150] As described above, in embodiments, the fiber 300, when extending across the spacing 140, may also move in the x-direction. Accordingly, the sigmoidal shape of the fiber 300, in such embodiments, will be three-dimensional. As such, the sigmoidal shape of the fiber 300 may further be described, in some embodiments, by the Logistic Function as follows:

[00151] In this representation of the Logistic Function, the value “z” is the position of the fiber 300 in the z-direction within the spacing 140, with a minimum value of z = -0.5w (w being the transition width (w) of the spacing 140), at the interior surface 114 of the planar fiber interface 110, and a maximum value of z = +0.5w, at the interior surface 126 of the two-dimensional fiber interface 120. The value “^^” is the lateral transition distance, in the x-direction, between the position of the fiber 300 at the interior surface 114 of the planar fiber interface 110 (where z = - 0.5w) and the position of the fiber 300 at the interior surface 126 of the two-dimensional fiber interface 120 (where z = +0.5w). The value “l2” is a length scaling parameter describing the sharpness of the S-shaped curve, and l2 may be determined by measuring, for a given dimensions w and h, an actual fiber length of the portion of the fiber 300 within the spacing 140. [00152] In some embodiments, the sigmoidal shape, in the x-direction, of the fiber 300 in the spacing 140 may also be described by the Error Function, which takes the following form:

[00153] In the Error Function, as in the Logistic Function, value “z” is the position of the fiber 300 in the z-direction within the spacing 140, with a minimum value of z = -0.5w (w being the transition width (w) of the spacing 140), at the interior surface 114 of the planar fiber interface 110, and a maximum value of z = +0.5w, at the interior surface 126 of the two-dimensional fiber interface 120. The value “^^” is the lateral transition distance, in the x-direction, between the position of the fiber 300 at the interior surface 114 of the planar fiber interface 110 (where z = - 0.5w) and the position of the fiber 300 at the interior surface 126 of the two-dimensional fiber interface 120 (where z = +0.5w) . The value “l₃” is a length scaling parameter describing the sharpness of the S-shaped curve, and l3 may be determined by measuring, for a given dimensions w and h, an actual fiber length of the portion of the fiber 300 within the spacing 140. [00154] For each of the Logistic Function and the Error Function, an instantaneous radius of curvature in the x-direction (^x) may be described by:

[00155] In equation (7), x’ and x” are the first and second derivatives of either of the Logistic Function (equation (5)) or the Error Function (equation (6)) with respect to z. [00156] A sigmoidal shape of a fiber is thereby, in part, defined by a difference in position, in the x-y plane) between an opening of the planar fiber interface 110 from which the fiber extends and an opening of the two-dimensional fiber interface 120 into which the fiber extends. If the opening in the planar fiber interface 110 has a different position in the y-plane (defining a transition height (h) of the fiber) from the opening in the two-dimensional fiber interface 120, the fiber extending between the openings will have a sigmoidal shape in the y-plane and the sigmoidal shape will have a form similar to the sigmoidal shape of the fiber 300 in the y-plane, as depicted in FIG.3. If the opening in the planar fiber interface 110 has a different position in the x-plane (defining a lateral transition distance (^^) of the fiber) from the opening in the two-dimensional fiber interface 120, the fiber extending between the openings will have a sigmoidal shape in the x-plane similar to that depicted in FIG.3. If the opening in the planar fiber interface 110 has a different position in the x-plane (defining a lateral transition distance (^^) of the fiber) and in the y-plane (defining a transition height (h) of the fiber) from the opening in the two-dimensional fiber interface 120, the fiber extending between the openings will have a sigmoidal shape in the x-plane and a sigmoidal shape in the y-plane, and each sigmoidal shape will be similar to the sigmoidal shape in the y- plane of the fiber 300 depicted in FIG.3. [00157] Referring now to FIG.4, in this embodiment, the optical fiber converter 100 includes a bridge 400 attaching the planar fiber interface 110 to the two-dimensional fiber interface 120. In this embodiment, the optical fiber converter 100 may be formed as a single component. In embodiments, the bridge 400 may improve stability of the optical fiber converter 100, coupling quality and/or integrity of the plurality of fibers 130, and/or decrease a probability of failure of the plurality of fibers 130. In embodiments, the bridge 400 may be formed of a glass, a glass-ceramic, polymer, etc. In embodiments, the bridge 400 may be formed of a plastic and, in certain such embodiments, the plastic may be injection molded. [00158] In this embodiment, the optical fiber converter 100 also includes guide holes 410, 420. Each of the guide holes 410, 420 are configured to house alignment pins, which are subsequently depicted in FIG.6 and are described in further detail below. The guide holes 410, 420 may be, for example, etched holes in the two-dimensional fiber interface 120. In the illustrated embodiment, the guide holes 410, 420 are situated to either side of the rows of openings 122, 124. In embodiments, the rows of openings may be recessed on an interior surface of the two-dimensional fiber interface 120 relative to the guide holes as depicted. The guide holes 410, 420 may be used for receiving alignment pins from an optical connector, for example. [00159] Referring to FIG.5, in this embodiment, the top surface 116 of the planar fiber interface 110 is covered by a plate 500, which functions as a lid, covering the v-groove array 112 and the planar fiber array 132. The plate 500 may secure the planar fiber array 132 within the v-groove array 112, thereby improving stability of the planar fiber array 132, coupling quality and/or integrity of the planar fiber array 132, and/or decrease a probability of failure of the planar fiber array 132. In embodiments, the plate 500 may be formed of any suitable material, such as the same or different material as the planar fiber interface. Accordingly, in the embodiment of FIG.5, the openings defining the planar fiber array 132 are positioned within the v-groove array 112 and between the plate 500 and the top surface 116. In embodiments, the plate 500 may be attached to either or both of the v-groove array 112 and/or the top surface 116 of the planar fiber interface 110 by an adhesive, such as described above. [00160] Referring to FIG. 6, in this embodiment, the optical fiber converter 100 includes alignment pins 610, 620. The alignment pins 610, 620 extend through the guide holes 410, 420, respectively. In embodiments, the alignment pins 610, 620, may press against the top surface 116 of the planar fiber interface 110, and, by pressing against the top surface 116 of the planar fiber interface 110, the alignment pins 610, 620 may improve stability of the optical fiber converter 100. However, in other embodiments, the alignment pins 610, 620 may not press against the top surface 116 of the planar fiber interface 110 and, in certain such embodiments, the alignment pins 610, 620 may not contact the top surface 116 of the planar fiber interface 110 at all. Further, the alignment pins 610, 620 may extend into a first optical element coupled to the exterior surface 113 of the planar fiber interface 110 and/or a second optical element coupled to the exterior surface 125 of the two-dimensional fiber interface 120, thereby providing passive connector alignment between the optical fiber converter 100 and either or both of the first optical element coupled to the exterior surface 113 of the planar fiber interface 110 and/or the second optical element coupled to the exterior surface 125 of the two-dimensional fiber interface 120. The guide holes 410, 420 extend through the exterior surface 125 of the two-dimensional fiber interface 120, enabling the alignment pins 610, 620 to couple to or be received from a second optical element coupled to the exterior surface 125 of the two-dimensional fiber interface 120. [00161] Still referring to FIG.6, in embodiments, to accommodate the alignment pins 610, 620, the top surface 116 of the planar fiber interface 110 may be positioned lower relative to the rows of openings 122, 124 of the two-dimensional fiber interface 120. Accordingly, in such embodiments, and as described above, an axis of the planar fiber array 132 may not be aligned with an axis about with the rows of openings 122, 124 of the two-dimensional fiber interface 120 are centered and may instead be offset by a distance in the y-direction. Accordingly, in such embodiments, fibers of the plurality of fibers 130 may move more or less than +/-0.5h when extending across the spacing 140 from the planar fiber interface 110 into the two-dimensional fiber interface 120. [00162] Referring to FIGS. 1B and 6, the alignment pins 610, 620 may be received from the second optical element 104 and extend through the guide holes 410, 420. Accordingly, in such embodiments, the alignment pins 610, 620 may thereby provide passive alignment between the optical fiber converter 100, the two-dimensional fiber interface 120, and/or the planar fiber interface 110. [00163] Though not depicted, in embodiments it is contemplated that the planar fiber interface 110 may additionally or alternatively comprise guide holes instead of or in addition to guide holes 410,420. In certain such embodiments, alignment pins extending through the guide holes may be the alignment pins 610, 620. In other such embodiments, alignment pins extending through the guide holes may be separate alignment pins from the alignment pins 610, 620, and, referring to FIG.1B, in embodiments, alignment pins of the planar fiber interface 110 may be, e.g., received from the first optical element 102. [00164] Referring to FIG. 7, and as noted above, the openings of the two-dimensional fiber interface 120 may not be holes (as in, e.g., the embodiment of FIG.1), and may instead, as in this embodiment, be defined by a v-groove array 700. In this embodiment, the two-dimensional fiber interface may have a first plate 710 and a second plate 720, which when combined provide a v- groove array 700 as depicted. The first plate 710 is interleaved with the second plate 720, as the first plate 710 has, on a bottom surface 711, a v-groove pattern 712 that corresponds with a v- groove pattern 722 of a top surface 721 of the second plate 720 to form the v-groove array 700 as an interleaved v-groove array which defines the rows of openings 122, 124. To form the interleaved v-groove array, each of the v-groove patterns 712, 722 has a form opposite the other of the v-groove patterns 712, 722. Accordingly, in the embodiment of FIG.7, the first row 122 is offset, in the x-direction, from the second row of openings 124, such that the first row of openings 122 has differing start and end points, in the x-direction, then start and end points of the second row of openings 124. By interleaving the v-groove patterns 712, 722, openings of the rows of openings 122, 124 are formed from gaps between the plates 710, 720. [00165] The plates 710, 720 may provide corresponding grooves that collectively define guide holes 730, 740, which may house alignment pins, such as in the manner described above. In this embodiment, the first plate 710 and the second plate 720 are separate components, which may be attached to one another. In embodiments, the plates 710, 720 may be attached to each other by an adhesive. In embodiments, the plates 710, 720 may be attached to each other by a thermally stable adhesive. In embodiments, the plates 710, 720 may be attached to each other by soldering. [00166] Referring to FIG.8, in this embodiment, the two-dimensional fiber interface 120 has a first plate 810, a second plate 820, and a spacer plate 800 between the first plate 810 and the second plate 820. In this embodiment, the first row of openings 122 is formed by gaps between the spacer plate 800 and a v-groove pattern 812 on a bottom surface 811 of the first plate 810, while the second row of openings 124 is formed by gaps between the spacer plate 800 and a v-groove pattern 822 on a top surface 821 of the second plate 820. [00167] When compared to the embodiment of FIG.7, the embodiment of FIG.8 may enable the rows of openings 122, 124 to be defined by v-groove patterns yet not have differing start and end points, in the x-direction. However, in other embodiments, differences between the v-groove patterns 812, 822 may form rows of openings having differing start and end points, in the x- direction. [00168] In embodiments, the spacer plate 800 may not extend along an entire width of the plates 810, 820, such that the plates 810, 820 may, despite the presence of the spacer plate 800 between the plates 810, 820, nonetheless define guide holes 830, 840. In embodiments, either or both of the plates 810, 820 may be formed of a glass, a glass-ceramic, a polymer, etc. In embodiments, the spacer plate 800 may be formed of a glass, a glass-ceramic, a polymer, etc. In embodiments, the plates 810, 820 may each be formed of the same material. In embodiments, the plates 810, 820 may be formed of differing materials. In embodiments, the spacer plate 800 may be formed of the same material as either or both of the plates 810, 820. In embodiments, the spacer plate 800 may be formed of a different material than either or both of the plates 810, 820. [00169] The spacer plate 800 has a spacer height (hs), wherein the spacer height (hs) defines a distance between the plates 810, 820, and so the row height (hr) of the rows of openings 122, 124 may be a sum of the spacer height (h_s) and a diameter (e.g., a cladding diameter and/or a coated diameter) of the plurality of fibers 130. The spacer height (hs) may thereby be chosen to accommodate a row height of a two-dimensional fiber array of a second optical element coupled to the exterior surface 125 of the two-dimensional fiber interface 120. For example, in embodiments, MPO connector ferrules may have a standard row height (h_r) of 0.5 mm, and so, in embodiments wherein the two-dimensional fiber interface 120 is configured to couple to an MPO connector, the spacer height (h_s) may thereby be sized to provide the two-dimensional fiber array 134 with a row height (h_r) of 0.5 mm. For example, to provide the two-dimensional fiber array 134 with a row height (hr) of 0.5 mm in embodiments wherein the cladding diameter of the plurality of fibers 130 is 0.125 mm, the spacer height (hs) may be 0.375 mm. [00170] As described above, the two-dimensional fiber interface 120 may, in embodiments, have three rows of openings. Referring to FIGS.9A-9B, in this embodiment, the two-dimensional fiber array 134 is defined by a first row of openings 921, a second row of openings 922, and a third row of openings 923 in the two-dimensional fiber interface 120. The single row of openings 111, in this embodiment, remains aligned along the axis 112A. In this embodiment, the second row of openings 922 is also aligned along the axis 112A, such that the second row of openings 922 and the planar fiber array 132 have equal heights (as measured in the y-direction). The first row of openings 921 and the third row of openings 923 are thereby offset, in the y-direction, from the second row of openings 922 (as measured from the center of openings of each of the rows of openings 921, 922, 923) by +0.5h and -0.5h, respectively. Accordingly, fibers of the plurality of fibers 130 extending into the rows of openings 921, 923 move +/-0.5h in the y-direction when extending across the spacing 140, while fibers of the plurality of fibers 130 extending into the second row of openings 922 may not move in the y-direction when extending across the spacing 140. [00171] In other embodiments, as described above, the rows of openings 921, 922, 923 may not be centered around the axis 112A, and the second row of openings 922 may instead be offset, in the y-direction, from the axis 112A (and, thereby, the planar fiber array 132. In further embodiments, the two-dimensional fiber interface 120 may comprise four or more rows of openings, and, in embodiments, the number of rows of openings in the two-dimensional fiber interface 120 may be limited only by a height of the two-dimensional fiber interface 120. [00172] Referring to FIG.10, an exemplary process 1000 for converting a planar fiber array to a two-dimensional fiber array is generally depicted. In the following description of the exemplary process 1000, exemplary reference is made to embodiments of FIG. 1A, 1B, 5, 6, 7, 8, and 9B. However, the exemplary process 1000 and/or any individual blocks of the exemplary process 1000 may refer to any of the embodiments described herein, including any of the embodiments of any of FIGS. 1A-9B. The exemplary process 1000 may include a greater or fewer number of steps, taken in any order, without departing from the scope of the present disclose. [00173] Referring again to FIGS.1A and 10, at a block 1010, the exemplary process may include arranging a plurality of optical fibers 130 in the single row of openings 111 of a planar fiber interface 110. In embodiments, the plurality of optical fibers 130 may be arranged within the planar fiber interface 110 as the planar fiber array 132. [00174] Referring again to FIGS.1A and 10, the exemplary process 1000 may include, at block 1020, extending a first portion of optical fibers of the plurality of optical fibers 130 from the planar fiber interface 110, across the spacing 140, and into the first row of openings 122 of the two- dimensional fiber interface 120. [00175] Referring again to FIGS.1A and 10, the exemplary process 1000 may further include, at block 1030, extending a second portion of optical fibers of the plurality of optical fibers 130 from the planar fiber interface 110, across the spacing 140, and into a second row of openings 124 of the two-dimensional fiber interface. In some embodiments, every other fiber is placed in the first row of openings 122 every intervening fiber is positioned within the second row of openings 124. This may reduce pitch transitions when moving from the single row of openings 111 to the first row of openings 122 or the second row of openings. [00176] Referring to FIGS.1B and 10, the exemplary process 1000 may further include coupling the first optical element 102 to the exterior surface 113 of the planar fiber interface 110. [00177] Referring to FIGS.1B and 10, the exemplary process 1000 may further include coupling the second optical element 104 to the exterior surface 125 of the two-dimensional fiber interface 120. Referring to FIGS.1B, 6, and 10, in embodiments, the exemplary process 1000 may continue with extending at least one of the alignment pins 610, 620 of the second optical element 104 through at least one of the guide holes 410, 420 of the two-dimensional fiber interface. [00178] Referring to FIGS. 1A, 9B, and 10, the exemplary process 1000 may further include extending a third portion of optical fibers of the plurality of optical fibers 130 from the planar fiber interface 110, across the spacing 140, and into the third row of openings 923 of the two- dimensional fiber interface. In this case, were the plurality of fibers be divided into groups of three, every first fiber may be extended into the first row of openings 921, every second fiber may be extended into the second row of openings 922, and every third fiber may be extended into the third row of openings to assist in minimizing pitch transitions. Other configurations are contemplated and possible [00179] Referring to FIGS. 1A and 10, the exemplary process 1000 may further include positioning the material 142 within the spacing 140, wherein the material 142 encapsulates the plurality of optical fibers 130 within the spacing 140. [00180] Referring again to FIGS. 1A and 10, the exemplary process 1000 may further include applying an adhesive to attach the plurality of optical fibers 130 to the planar fiber interface 110. In some embodiments, the material 142 may be the adhesive. [00181] Referring again to FIGS. 1A and 10, the exemplary process 1000 may further include applying an adhesive to attach the plurality of optical fibers 130 to the two-dimensional fiber interface 120. In some embodiments, the material 142 may be the adhesive. [00182] Referring to FIGS. 7 and 10, the exemplary process may further include attaching the first plate 710 of the two-dimensional fiber interface 120 to the second plate 720 of the two- dimensional fiber interface 120, wherein the first row of openings 122 and the second row of openings 124 are formed from gaps between the first plate 710 and the second plate 720. [00183] Referring to FIGS. 8 and 10, the exemplary process may further include attaching the first plate 810 of the two-dimensional fiber interface 120 to the spacer plate 800 and attaching the second plate 820 of the two-dimensional fiber interface 120 to the spacer plate 800, wherein the first row of openings 122 is formed by gaps between the first plate 810 and the spacer plate 800 and wherein the second row of openings 124 is formed by gaps between the second plate 820 and the spacer plate 800. Referring to FIGS. 5 and 10, the exemplary process may further include attaching the plate 500 to any, some, or all of the surfaces 116, 117, 118 of the planar fiber interface 110, wherein the plurality of optical fibers 130 are arranged between the plate 500 and any, some, or all of the surfaces 116, 117, 118 of the planar fiber interface 110. EXAMPLES [00184] In order that various embodiments be more readily understood, reference is made to the following examples, which are intended to illustrate various embodiments of the optical fiber converters described herein. [00185] Referring now to FIGS. 11A-11B, graph 1110 is a plot of the transition height versus distance (in the z-direction) for the Logistic Function given by equation (2) with h = 0.5 mm and l0 = 0.4 mm, and the corresponding variation of the radius of curvature is shown in a graph 1120. The minimum radius of curvature is less than 5 mm, but this small bend radius regime spans a length that is only a few tenths of mm, so the accumulated bend loss through the spacing will be low. The transition width for the example of FIGS.11A-11B is w = 4.25 mm. [00186] Referring now to FIGS. 12A-12B, graph 1210 is a plot of the transition height versus distance for the Error Function given by equation (3) with h = 0.25 mm and l₁ = 0.4 mm, and the corresponding variation of the radius of curvature is shown in a graph 1220. The minimum radius of curvature is less than 5 mm, but this small bend radius regime spans a length that is only a few tenths of mm, so the accumulated bend loss through the spacing will be low. The transition width for the example of FIGS.12A-12B is w = 3.3 mm. [00187] Referring to FIGS. 11A-12B, the graphs 1110, 1120, 1210, 1220 illustrate that the Logistic and Error Functions yield the same qualitative shape for the spacing, but the shapes and widths of the small-bend-radius regions are different. Accordingly, the Logistic and Error functions may illustrate a different sigmoidal shape, despite using the same prior values. [00188] Referring to FIGS. 13A-B, graphs 1310, 1320 are each plots of a minimum radius of curvature versus a transition width (w) as calculated by the Logistic Function (in the graph 1310) and the Error Function (in graph 1320), respectively. The modelled data are plotted for h-values of 1.0, 0.75, 0.5 and 0.25 mm. The transition length (the transition length d being, referring to FIG.1A, a length of a portion of the fiber in the spacing 140) modelled using the Error Function is about 25% smaller than the transition length modelled using the Logistic Function. The total fiber length under the transition region is a function of the chosen sigmoid formula (e.g., the Error Function or the Logistic Function), transition width (w), and transition height (h), so measuring that length can help finding which sigmoidal function (the Error Function or the Logistic Function) best describes the shape of the transition region. [00189] For the fiber routing scenarios of FIGS.11A-13B, four fiber examples are summarized below in Table 1. These fibers have a range of macrobend resistances which fall into different categories of the ITU-T G.657 standard, “SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS; Transmission media and optical systems characteristics –Optical fibre cables.” Each fiber example may have different cladding and coating diameters and maintain the same bend loss characteristics. For example, Fiber 1 may have a cladding diameter of 80 microns or 100 microns and/or a coating diameter of 165 microns, 180 microns, 190 microns, or 200 microns. Table 1

[00190] The bend resistance of an optical fiber, described herein as “bend loss,” may be gauged by induced attenuation under prescribed test conditions as specified by the IEC-60793-1-47 standard, “Measurement methods and test procedures - Macrobending loss.” For example, the test condition can entail deploying or wrapping the fiber one or more turns around a mandrel of a prescribed diameter, e.g., by wrapping one, two or five turns around either an 8, 9, 10, 11, 12, 13, 14, 15 mm, 20 mm, or 30 mm or similar diameter mandrel (e.g. “1×15 mm diameter bend loss” or the “1×20 mm diameter bend loss” or the “1×30 mm diameter bend loss”) and measuring the increase in attenuation per turn. [00191] When measuring constant-radius bend-loss of a fiber, inaccuracies in measurement may occur due to oscillations in the bend response due to interference between the energy wave transmitted through a core of the fiber and whispering gallery modes in cladding of the fiber. Referring to FIG. 14A, an example of this phenomenon is depicted in graph 1410, which is the bend loss of Fiber 1 measured for a mandrel diameter of 12 mm. [00192] This measurement artefact may be overcome by performing the following steps: (1) measuring bend loss of the fiber according to the IEC-60793-1-47 standard for 5 wraps around mandrel diameters of 11, 12, 13, 14, and 15 mm and for 2 wraps around mandrel diameters of 8, 9 and 10 mm; (2) computing the average bend loss per turn and the average bend loss in the O- band (1270-1330 nm) and in the C-band (1530-1570 nm); (3) plotting the average bend loss in the O- and C-bands versus the mandrel diameter; and (4) fitting the average bend losses to an exponential function:

[00193] In equation (8), B is the bend loss, R is the bend radius (one-half of the bend diameter),^ B₀^is the bend loss coefficient, and^D^is the bend loss exponential decay coefficient. [00194] Referring to FIG.14B, graph 1420 illustrates the outcome of following steps (1)-(4), as described above, for Fiber 1 of Table 1, which has characteristic bend loss and exponential decay coefficients in the C-band of B0 = 2.2167 dB/turn and D^= 0.384 mm^-1, respectively. Referring to FIG.15, graph 1500 illustrates results for Fibers 3 and 4 in the C-band, and the results depicted in the graph 1500 are analogous to the results for Fiber 1 depicted in the graph 1420. [00195] The average bend losses, as determined by equation (8) for each fiber parameterized according to steps (1)-(4), as described above, can be combined with the instantaneous radius of curvature across the transition region (e.g. as shown in the graph 1120 of FIG.11B and the graph 1220 of FIG.12B) and integrated to yield the total bend loss:

[00196] Referring to FIGS. 16A-17B, in graphs 1610, 1620, 1710, 1720 the integrated bend losses in the C-band are plotted versus the transition width (w) region for Fibers 1-4 (as referenced in Table 1) and h-values of 1.0 mm (in the graph 1610), 0.75 mm (in the graph 1620), 0.5 mm (in the graph 1710), and 0.25 mm (in the graph 1720). These modeled results assume that the shape of the transition region is described by the Logistic Function (equations (1) and (2), as described above), but the results are qualitatively similar when the shape of the transition region is described by the Error Function (equation (3), as described above). The integrated bend losses for Fibers 1 and 2 is less than 0.2 dB, even when the width of the transition region is less than 4 mm and the minimum radius of curvature is less than 2 mm. Fibers 3 and 4 are less bend-insensitive than Fibers 1 and 2, but the integrated bend losses are still less than 0.2 dB when the transition heights are less than about 0.5 mm and 0.3 mm, respectively. [00197] Referring to FIGS.18A-18B, graphs 1810, 1820 show the analogous results for Fibers 3 and 4 in the O-band for transition regions characterized by Logistic Function. Referring to FIGS. 19A-19B, graphs 1910, 1920 show the analogous results for Fibers 3 and 4 in the O-band for transition regions characterized by Error Function. The total bend losses are less than 0.1 dB, even when the width of the transition region is less than 4 mm. As noted above, the magnitudes of the bend losses are approximately equal, but the Error Function yields a transition length d that is about 25% smaller than with the Logistic Function. [00198] Embodiments described herein may provide low predicted failure probabilities. Accordingly, predicted failure probabilities for fibers having differing cladding diameters, transition heights, and transition lengths for usage in embodiments described herein are described below. [00199] An explanation of mechanical reliability, and usage of such to determine predicted failure probabilities, can be found in “Optical Fiber Mechanical Reliability Modeling Extended to Small Bend Radii,“ by G. Scott Glaesemann and Yin Shu (Paper 14-6, 2021 International Wire and Cable Symposium), which is incorporated by reference herein. In this model, a perimeter of an optical fiber in a circular bend configuration is divided into 360 sectors, with each sector corresponding to S/180 degrees of arc. that are under constant tensile or compressive stress. The applied bending stress on the corresponding surface area for each sector is then determined as a function of the instantaneous bend radius R(z), and the failure probability is obtained by integrating over the trajectory of the fiber. [00200] Referring to FIGS. 20A-20B, graphs 2010, 2020 illustrate the predicted failure probability and failure probability versus time for individual fibers with 125 ^m cladding diameters that are bent in a sigmoidal curve described by the Logistic Function with 0.5h = 0.5 mm and a 5.45 mm transition length. Referring to FIGS.20C-20D, graphs 2030, 2040 illustrate the predicted failure probability and failure probability versus time for individual fibers with 80 ^m cladding diameters that are bent in a sigmoidal curve described by the Logistic Function with 0.5h = 0.5 mm and a 5.45 mm transition length. The failure probabilities for an individual fiber are quite low, but they need to be multiplied by the number of fibers in the pitch converter (e.g., 16, 24, or 32). [00201] Referring to FIGS. 21A-21B, graphs 2110, 2120 depict predicted failure probabilities for a single fiber with an 80 micron cladding diameter as a function of the transition length for transition heights of 1.0 mm, 0.75 mm, 0.5 mm, and 0.25 mm. The graphs 2110, 2120 assume that the sigmoidal shape of the fiber is described by the Logistic and the Error Function, respectively. [00202] Referring to FIGS. 22A-22B, graphs 2210, 2220 depict predicted failure probabilities for a single fiber with a 125 micron cladding diameter as a function of the transition length for transition heights of 1.0 mm, 0.75 mm, 0.5 mm, and 0.25 mm. The graphs 2210, 2220 assume that the sigmoidal shape of the fiber is described by the Logistic and the Error Function, respectively. [00203] Below, we consider, for multiple fibers in an optical fiber converter, two scenarios: (a) 16 fibers are straight and the other 16 transition by h = 0.5 mm to reach the second row, and (b) the FAU is centered with the MPO ferrule, and 16 of the fibers arc up by h = 0.25 mm and 16 arc down by h = 0.25 mm. [00204] Referring to FIGS. 23A-24B, graphs 2310, 2320 depict predicted failure probabilities for 16 fibers (scenario (a)) with 80 micron cladding diameters as a function of the transition length for transition heights of 1.0, 0.75, 0.5 and 0.25 mm. The graphs 2310, 2320 assume that the sigmoidal shape of the fiber is described by the Logistic and the Error Function, respectively. Analogous results for 16 fibers with 125 micron cladding diameters are plotted in graphs 2410, 2420. The graphs 2410, 2420 assume that the sigmoidal shape of the fiber is described by the Logistic and the Error Function, respectively. For the graphs 2310, 2320 and the graphs 2410, 2420, failure probabilities for other transition heights are also plotted for completeness. [00205] Referring to FIGS. 25A-26B, graphs 2510, 2520 depict predicted failure probabilities for 32 fibers (scenario (b)) with 80 micron cladding diameters as a function of the transition length for transition heights of 1.0, 0.75, 0.5 and 0.25 mm. The graphs 2510, 2520 assume that the sigmoidal shape of the fiber is described by the Logistic and the Error Function, respectively. Analogous results for 32 fibers with 125 micron cladding diameters are plotted in graphs 2610, 2620. The graphs 2610, 2620 assume that the sigmoidal shape of the fiber is described by the Logistic and the Error Function, respectively. For the graphs 2510, 2520 and the graphs 2610, 2620, failure probabilities for other transition heights are also plotted for completeness. [00206] It should not be understood that embodiments of the present disclosure are directed to optical fiber converters having a small form factor and able to transition an array of fibers from a planar fiber array to a two-dimensional fiber array. Accordingly, converters such as described herein may not add substantial bulk to an optical assembly and may be used in optical assemblies requiring optical converters having small form factors. In embodiments, a planar fiber interface and a two-dimensional fiber interface of the converter may be mechanically decoupled from one another, as described in greater detail above. Mechanical decouplings of the planar fiber interface and the two-dimensional fiber interface may prevent force transfers between optical elements, thereby providing greater longevity to components [00207] It will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

CLAIMS What is claimed is: 1. An optical fiber converter comprising: a planar fiber interface defining a single row of openings configured to receive a plurality of optical fibers; and a two-dimensional fiber interface spaced from the planar fiber interface by a spacing and defining at least a first row of openings and a second row of openings configured to receive the plurality of optical fibers from the planar fiber interface, wherein, when assembled with the plurality of optical fibers: a first portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the first row of openings of the two-dimensional fiber interface; a second portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the second row of openings of the two- dimensional fiber interface.

2. The optical fiber converter of claim 1, wherein the spacing comprises a transition width (w) less than or equal to about 20 mm.

3. The optical fiber converter of claim 1 or claim 2, wherein the first row of openings and the second row of openings are separated by a row height (hr) and wherein the row height (hr) is less than or equal to about 1 mm and greater than or equal to about 0.25 mm.

4. The optical fiber converter of any one of claims 1-3, wherein: the planar fiber interface defines a first pitch between openings of the single row of openings; the two-dimensional fiber interface defines a second pitch between openings of the first row of openings and between openings of the second row of openings; and the first pitch is different from the second pitch.

5. The optical fiber converter of claim 4, wherein the second pitch is less than or equal to 300 ^m.

6. The optical fiber converter of any one of claims 1-5, wherein the single row of openings is provided by a v-groove array formed within a top surface of the planar fiber interface.

7. The optical fiber converter of any of one claims 1-6, wherein each of the planar fiber interface and the two-dimensional fiber interface define at least 16 openings.

8. The optical fiber converter of any of one claims 1-7, further comprising a bridge attaching the planar fiber interface to the two-dimensional fiber interface.

9. The optical fiber converter of any one of claims 1-8, wherein the two-dimensional fiber interface comprises a first plate defining a first v-groove pattern and a second plate defining a second v-groove pattern.

10. The optical fiber converter of claim 9, wherein the two-dimensional fiber interface comprises a spacer plate between the first plate of the two-dimensional fiber interface and the second plate of the two-dimensional fiber interface.

11. The optical fiber converter of claim 9, wherein the first v-groove pattern and the second v- groove pattern are interleaved to provide an interleaved v-groove array.

12. The optical fiber converter of any one of claims 1-11, wherein the two-dimensional fiber interface defines a guide hole configured to house an alignment pin.

13. The optical fiber converter of any one of claims 1-12, wherein the two-dimensional fiber interface further defines a third row of openings configured to receive the plurality of optical fibers from the planar fiber interface, wherein, when assembled with the plurality of optical fibers, a third portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the third row of openings of the two-dimensional fiber interface.

14. An optical fiber converter comprising: a planar fiber interface defining a single row of openings configured to receive a plurality of optical fibers; a two-dimensional fiber interface spaced from the planar fiber interface by a spacing and defining at least a first row of openings and a second row of openings configured to receive the plurality of optical fibers from the planar fiber interface; and a plurality of optical fibers housed within the planar fiber interface as a planar fiber array and within the two-dimensional fiber interface as a two-dimensional fiber array and extending between the planar fiber interface and the two-dimensional fiber interface, wherein: a first portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the first row of openings of the two-dimensional fiber interface; and a second portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the second row of openings of the two- dimensional fiber interface.

15. The optical fiber converter of claim 14, wherein at least some optical fibers of the plurality of optical fibers comprise, within the spacing, a sigmoidal shape defined by ^

^{^}

െ_ଶ, wherein: h is a transition height of the optical fiber; y is a vertical position of the optical fiber equal to 0 at a height of the planar fiber interface; the spacing comprises a transition width (w); z is a position of the optical fiber between an interior surface of the planar fiber interface and an interior surface of the two-dimensional fiber interface, wherein z is equal to, at the interior surface of the planar fiber interface, -0.5w and equal to, at the interior surface of the two- dimensional fiber interface, +0.5w; and l0 is a length scaling parameter.

16. The optical fiber converter of claim 14, wherein at least some optical fibers of the plurality of optical fibers comprise, within the spacing, a sigmoidal shape defined by: wherein: h is a transition height of the optical fiber; y is a vertical position of the optical fiber equal to 0 at a height of the planar fiber interface; the spacing comprises a transition width (w); z is a position of the optical fiber between an interior surface of the planar fiber interface and an interior surface of the two-dimensional fiber interface, wherein z is equal to, at the interior surface of the planar fiber interface, -0.5w and equal to, at the interior surface of the two- dimensional fiber interface, +0.5w; and l₁ is a length scaling parameter.

17. The optical fiber converter of any one of claims 15-16, wherein the transition width (w) is less than or equal to about 20 mm.

18. The optical fiber converter of any one of claims 14-17, wherein a flexible material encapsulating the plurality of optical fibers is positioned within the spacing.

19. The optical fiber converter of claim 18, wherein the flexible material comprises an adhesive.

20. The optical fiber converter of any one of claims 14-19, wherein each optical fiber of the plurality of optical fibers comprises a macrobend loss less than or equal to 0.2 dB.

21. The optical fiber converter of any one of claims 14-20, wherein each optical fiber of the plurality of optical fibers comprises a cladding diameter greater than or equal to 50 ^m and less than or equal to 125 ^m.

22. The optical fiber converter of claim 21, wherein the cladding diameter is less than or equal to 100 ^m.

23. The optical fiber converter of claim 22, wherein the cladding diameter is less than or equal to 80 ^m.

24. The optical fiber converter of claim 23, wherein the cladding diameter is less than or equal to 62.5 ^m. 25. The optical fiber converter of any one of claims 14-24, wherein the first row of openings and the second row of openings are separated by a row height (hr) and wherein the row height (hr) is less than or equal to about 1 mm and greater than or equal to about 0.

25 mm.

26. The optical fiber converter of any one of claims 14-25, wherein: the planar fiber array comprises a first pitch; the two-dimensional fiber array comprises a second pitch; and the first pitch is different from the second pitch.

27. The optical fiber converter of claim 26, wherein the second pitch is less than or equal to 300 ^m.

28. The optical fiber converter of any one of claims 14-27, wherein the single row of openings is provided by a v-groove array formed within a top surface of the planar fiber interface.

29. The optical fiber converter of any one of claims 14-28, wherein each of the planar fiber interface and the two-dimensional fiber interface define at least 16 openings.

30. The optical fiber converter of any one of claims 14-29, further comprising a bridge attaching the planar fiber interface to the two-dimensional fiber interface.

31. The optical fiber converter of any one of claims 14-30, wherein the two-dimensional fiber interface comprises a first plate defining a first v-groove pattern and a second plate defining a second v-groove pattern.

32. The optical fiber converter of claim 31, wherein the two-dimensional fiber interface comprises a spacer plate between the first plate of the two-dimensional fiber interface and the second plate of the two-dimensional fiber interface.

33. The optical fiber converter of claim 31, wherein the first v-groove pattern and the second v-groove pattern are interleaved to provide an interleaved v-groove array.

34. The optical fiber converter of any one of claims 14-33, wherein the two-dimensional fiber interface defines a guide hole configured to house an alignment pin.

35. The optical fiber converter of any one of claims 14-34, wherein the two-dimensional fiber interface further comprises a third row of openings configured to receive the plurality of optical fibers from the planar fiber interface, wherein, when assembled with the plurality of optical fibers, a third portion of optical fibers of the plurality of optical fibers extends across the spacing from the planar fiber interface into the third row of openings of the two-dimensional fiber interface.

36. A method for converting a planar fiber array to a two-dimensional fiber array, the method comprising: arranging a plurality of optical fibers in a single row of openings of a planar fiber interface, wherein the plurality of optical fibers are arranged within the planar fiber interface as a planar fiber array; extending a first portion of optical fibers of the plurality of optical fibers from the planar fiber interface, across a spacing, and into a first row of openings of a two- dimensional fiber interface; and extending a second portion of optical fibers of the plurality of optical fibers from the planar fiber interface, across the spacing, and into a second row of openings of the two- dimensional fiber interface; wherein the spacing separates the planar fiber interface and the two-dimensional fiber interface and wherein the plurality of optical fibers is arranged within the two-dimensional fiber interface as a two-dimensional fiber array.

37. The method of claim 36, further comprising coupling a first optical element to an exterior surface of the planar fiber interface.

38. The method of claim 36 or claim 37, further comprising coupling a second optical element to an exterior surface of the two-dimensional fiber interface.

39. The method of claim 38, further comprising extending at least one alignment pin of the second optical element through at least one guide hole of the two-dimensional fiber interface.

40. The method of any one of claims 36-39, further comprising extending a third portion of optical fibers of the plurality of optical fibers from the planar fiber interface, across the spacing, and into a third row of openings of the two-dimensional fiber interface.

41. The method of any one of claims 36-40, further comprising positioning a material within the spacing, wherein the material encapsulates the plurality of optical fibers within the spacing.

42. The method of any one of claims 36-41, further comprising applying an adhesive to attach the plurality of optical fibers to the planar fiber interface.

43. The method of any one of claims 36-42, further comprising applying an adhesive to attach the plurality of optical fibers to the two-dimensional fiber interface.

44. The method of any one of claims 36-43, further comprising attaching a first plate of the two-dimensional fiber array to a second plate of the two-dimensional fiber array, wherein the first row of openings and the second row of openings are formed from gaps between the first plate and the second plate.

45. The method of any one of claims 36-43, further comprising attaching a first plate of the two-dimensional fiber array to a spacer plate and attaching a second plate of the two-dimensional fiber array to the spacer plate, wherein the first row of openings is formed by gaps between the first plate and the spacer plate and wherein the second row of openings is formed by gaps between the second plate and the spacer plate.

46. The method of any one of claims 36-45, further comprising attaching a plate to a surface of the planar fiber interface, wherein the plurality of optical fibers are arranged between the plate and the surface of the planar fiber interface.