HK1140026B - Multi-fiber fiber optic receptacle and plug assembly - Google Patents

Abstract

A fiber optic receptacle and plug assembly adapted to be mounted within an opening through a wall of a connection terminal. The receptacle and plug define complimentary alignment and keying features for ensuring that the plug is mated with the receptacle in a predetermined orientation. An alignment sleeve is disposed within the plug for receiving a multi-fiber receptacle ferrule and a multi-fiber plug ferrule. The fiber optic receptacle and corresponding plug each include a biasing member assembly for urging the receptacle ferrule and the plug ferrule towards one another, wherein the biasing member assembly includes a round spring, a spring centering cuff and a ferrule boot that operatively engage the rear of the receptacle ferrule and the plug ferrule, respectively, to substantially center a spring biasing force on the end face of the receptacle ferrule and the plug ferrule.

Description

Multi-fiber optic receptacle and plug assembly

Technical Field

The present invention relates generally to fiber optic receptacle and plug assemblies, and more particularly to a multi-fiber optic receptacle and plug assembly that employs a Mechanical Transfer (MT) ferrule to interconnect a plurality of optical fibers in a communications network.

Background

Optical fiber is increasingly being used for broadband applications including voice, video and data transmission. As a result, fiber optic communications networks include a number of interconnection points that interconnect multiple optical fibers. Fiber optic communications networks also include a number of connection terminals, examples of which include, but are not limited to, Network Access Point (NAP) enclosures, radomes, drop enclosures, pedestals, Optical Network Terminals (ONTs), and Network Interface Devices (NIDs). In some instances, the connection terminal includes a splice port, typically an opening through an exterior wall of the terminal, for establishing a connection between optical fibers tapped from individual optical fibers of a distribution cable and one or more drop cables (drop cables), extended distribution cables, captive cables (tethers) or drop cables collectively referred to as "drop cables" that are pre-spliced. The connection terminal is used to easily extend a fiber optic communication service to a user. In this regard, fiber optic networks are being developed to provide "fiber to the curb" (FTTC), "fiber to the business" (FTTB), "fiber to the subscriber" (FTTH), "fiber to the premises" (FTTP), collectively "FTTx".

Conventional splice ports that open through an exterior wall of a connection terminal include receptacles for receiving a spliced optical fiber, such as a splice, within the connection terminal optically connected to an optical fiber of a distribution cable, such as within a splice tray or splice protector. Currently, these receptacles are relatively large in size because the connection terminals in which they are located do not limit the size of the receptacle. Additionally, prior receptacles include a receptacle housing that defines an interior cavity that receives a receptacle for receiving and aligning a mating ferrule. As previously described, one of the mating ferrules is mounted upon the end of an optical fiber that is optically connected to an optical fiber of the distribution cable within the connection terminal. Another mating ferrule is mounted upon the end of an optical fiber of a drop cable that is inserted into the receptacle from outside the connection terminal. The alignment sleeve of the receptacle assists in gross alignment of the ferrules, while the ferrule guide pins or other alignment means assist in more precise alignment of the opposing end faces of the ferrules.

Specifically, a fiber optic plug mounted on the end of a fiber optic drop cable is received into a receptacle through an external wall of the connection terminal. The plug typically includes a generally cylindrical plug body and a fiber optic connector including a plug ferrule disposed within the cylindrical plug body. The end of the cylindrical plug body is open or provided with an opening so that the ferrule is accessible, e.g., cleaned, within the plug body. The plug ferrule is mounted upon one or more optical fibers of the fiber optic drop cable such that mating the plug with the receptacle aligns the optical fibers of the drop cable with the optical fibers of the distribution cable that are each terminated within the connection terminal. During mating of the plug with the receptacle, the plug ferrule is inserted into one end of an alignment sleeve mounted within the receptacle. The configuration of conventional fiber optic receptacles is such that the alignment sleeve is minimally received into the open end of the plug body when the plug ferrule is inserted into the alignment sleeve.

Several different conventional fiber optic connectors have been developed, examples of which include, but are not limited to, SC, ST, LC, DC, MPT, MT-RJ, and SC-DC connectors. The size and shape of the ferrules of each of these conventional connectors are somewhat different. Correspondingly, the size and shape of the alignment sleeve and the plug body are somewhat different. Accordingly, in conventional practice, different fiber optic plugs and receptacles are used with different types of connectors and/or ferrules. In this regard, fiber optic receptacles generally define differently sized internal cavities corresponding to the size of the alignment sleeve and plug body received within the cavity and, in turn, corresponding to the ferrule of the fiber optic connector to be inserted into the alignment sleeve.

In addition to requiring the use of different fiber optic receptacles and plugs depending on the particular type of fiber optic splice, conventional receptacle and plug assemblies are also typically not very compact to allow for high density installation. On the other hand, current smaller assemblies are unable to meet the high tensile loads required for FTTx installations, including the requirements for 600lbs. drop cable pull tests, and are unable to handle large numbers of interconnections. Exposure to adverse environmental conditions is also a significant issue because current network plans suggest that outlets may remain unoccupied (i.e., without a mating plug) for an extended period of time. Based on the tensile load requirements and the need for durable environmental protection, there is a need to provide a robust fiber optic receptacle and corresponding fiber optic plug that is suitable for installation in a connection terminal or similar enclosure defining an external wall through which an optical fiber interconnection is to be routed. However, the need for a compact and sufficiently robust fiber optic receptacle configured to receive only fiber optic plugs having the same type of splice as the receptacle has not been addressed to date. There is also an unresolved need for a fiber optic receptacle and plug assembly that can accommodate an alignment sleeve and any type of optical splice, where the receptacle and plug define corresponding alignment and keying features (features). What has not yet been solved is a need for a fiber optic receptacle and plug assembly adapted to receive a Mechanical Transfer (MT) style ferrule in an opposed relationship in a low profile, environmentally sealed receptacle and plug having improved biasing means and forces that can be focused to ensure proper end-to-end physical contact.

Disclosure of Invention

One aspect of the present invention is a fiber optic receptacle and plug assembly having the same optical connector configuration. The corresponding receptacle and plug each include the same type of multi-fiber connector, such as, but not limited to, a Mechanical Transfer (MT) connector. The receptacle and plug are designed to be mass-installed in a compact and sufficiently robust assembly in both indoor and outdoor installation environments. For outdoor environments, both the receptacle and the plug are provided with improved sealing and increased mechanical strength against pulling forces compared to conventional optical connections. In one embodiment, the receptacle portion of the assembly may be disposed in a connector port (hereinafter "port") in a wall of the connection terminal. One or more receptacles may be installed in the connection terminal and remain unoccupied until needed. The alignment and keying features defined by the receptacle and plug allow a plug having the same optical connector configuration to mate with a corresponding receptacle in the correct orientation, once desired.

In another aspect, the present invention includes corresponding receptacle and plug assembly subassemblies that are robust, having multi-fiber ferrules. Each multi-fiber ferrule is biased within the receptacle and plug by a round spring. The ferrule boot combines the functions of sealing, tape guiding, and force centering. The sealing function prevents epoxy from leaking between the ferrule and the ferrule boot, thereby preventing contamination of the pin clip that may be used to retain a pair of guide pins in the ferrule. The rear end of the ferrule boot is provided with a tapered receiving window for insertion of a plurality of individual optical fibers or optical fiber ribbons. The ferrule boot also defines a convex domed-shaped surface having a center point axially aligned with a center point on the ferrule end face between two central optical fibers. A spring centering cuff is disposed on the ferrule boot to align the spring and couple the spring force to the ferrule boot. The cuff is disposed on the bearing surface of the ferrule boot to provide an axial spring force perpendicular to the tangential direction of the arcuate surface aligned with the center point on the end face of the ferrule. The round spring, spring centering cuff, and ferrule boot together provide a force centering function that properly aligns the optical fibers of the mating ferrule.

In another aspect, the present invention includes a fiber optic plug having an alignment sleeve, wherein the plug housing and the alignment sleeve define alignment and keying features that enable the plug to properly mate with a corresponding receptacle that defines alignment and keying features that are complementary to the features of the fiber optic plug. Thus, a fiber optic plug having a predetermined connector configuration can only be received into a receptacle having the same connector configuration. The excluding features of the alignment sleeve prevent mating of different fiber optic plugs and receptacles and, thus, damage to the opposing ferrules and/or optical fibers of a multi-fiber connector. The alignment sleeve helps the ferrules to make a coarse alignment, while the guide pins help the optical fibers to make a fine alignment. The receptacle also defines a shoulder portion having a predetermined shape that is received against an inner surface of a wall of the connection terminal, the wall defining an opening for receiving the ferrule, thereby securing the receptacle in the opening through the wall of the connection terminal and preventing rotation of the housing within the connector port.

In another aspect, the invention includes corresponding fiber optic receptacle and plug sub-assemblies. In a preferred embodiment, the receptacle subassembly comprises: a one-piece housing defining an internal cavity opening through opposing first and second ends, a receptacle seal, a receptacle dust cap assembly, an outer retaining ring, a multi-fiber ferrule, a pair of guide pins, a pin retainer clip, a ferrule boot, a centering cuff, a round spring, and a ferrule retainer. The plug sub-assembly includes a plug housing, a crimp band, a coupling nut, an alignment sleeve, and a plug pulling cap assembly. In another embodiment, the plug sub-assembly includes a plug crimp insert, a plug inner housing, a multi-fiber ferrule, a ferrule boot, a centering cuff, and a round spring. To mate the fiber optic plug with the fiber optic receptacle, the internal cavity of the receptacle receives a plug sub-assembly, including an alignment sleeve. The round springs of the receptacle and plug are engageable and bias the respective multi-fiber ferrules toward one another during mating.

Additional features and advantages of the invention 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 invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description present exemplary embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and serve to explain their principles and operation.

Drawings

FIG. 1 is a perspective view of a multi-fiber optic receptacle and plug assembly according to the present invention in a non-engaged state with respective dust caps and pull caps removed.

FIG. 2 is a perspective view of the multi-fiber optic receptacle and plug assembly of FIG. 1, showing the receptacle and plug mated.

Fig. 3 is a cross-sectional view of the mated receptacle and plug assembly of fig. 2 taken along line 3-3.

FIG. 4A is an exploded perspective view of the fiber optic receptacle of FIG. 1 including a one-piece housing, a multi-fiber ferrule, guide pins, a pin retaining clip, a ferrule boot, a spring centering cuff, a round coil spring, and a ferrule retainer.

FIG. 4B is an exploded perspective view of an alternative embodiment of the biasing member assembly of FIG. 4A, including a ferrule boot, a spring centering cuff, a round coil spring, and a multi-fiber ferrule.

Fig. 5 is a cross-sectional view of the fiber optic receptacle of fig. 4A taken along line 5-5 showing an assembled configuration.

Fig. 6 is an exploded perspective view of the fiber optic plug of fig. 1 including a plug sub-assembly, a housing, a crimp band, a coupling nut, an alignment sleeve, and a pulling cap assembly.

Fig. 7 is a cross-sectional view of the fiber optic plug of fig. 6 taken along line 7-7, illustrating an assembled configuration.

FIG. 8 is an exploded perspective view of the plug sub-assembly of FIG. 6 including a crimp insert, an inner housing, a multi-fiber ferrule, a ferrule boot, a spring centering cuff, and a round spring.

Fig. 9 is a cross-sectional view of the plug sub-assembly of fig. 8 taken along line 9-9, showing an assembled configuration.

FIG. 10 is an end view of the fiber optic receptacle and fiber optic plug of FIG. 1 shown in an unengaged state to illustrate alignment and keying features of the receptacle and plug assemblies.

Detailed Description

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. One embodiment of the multi-fiber optic receptacle and plug assembly of the present invention is shown in fig. 1, wherein the fiber optic receptacle and corresponding fiber optic plug are generally indicated by the numerals 20 and 22, respectively.

Referring now to FIGS. 1-10, exemplary embodiments of a fiber optic receptacle 20 and a corresponding large fiber optic plug 22 are shown. Although not shown, the receptacle 20 is typically mounted in a connector port defined by a wall of an enclosure such as a connection terminal in a fiber optic communications network. In a particularly preferred embodiment, the receptacle 20 is mounted in an opening formed through an external wall of a connection terminal such that a plug 22 mounted on the end of a fiber optic drop cable can be easily inserted into the receptacle 20 to extend the communications network to a subscriber premises (e.g., a residence or business). The receptacle 20 and the plug 22 cooperate to optically connect the plurality of optical fibers of the plug 22 with a plurality of optical fibers terminated in a connection terminal from a distribution cable. It should be understood, however, that the receptacle 20 may be mounted to other structures, such as the interior walls of a re-enterable connection terminal, or may be used as a separate interconnection component, such as in field communications, to interconnect optical transmitting and receiving devices. Each connector port is operable to receive a receptacle 20 and at least one connectorized optical fiber from within the connection terminal. The connector port is further operable to receive a plug 22 comprising at least one connectorized optical fiber of a drop cable that is inserted into the receptacle 20 from outside the connection terminal. A plug 22 is mounted on the end of the drop cable and is adapted to mate with a corresponding receptacle 20. The receptacle 20 and the plug 22 may be used to align and hold two optical fibers in opposing relation to transmit signals. In a particular embodiment, opposing optical fibers are aligned with and held in physical contact with each other. Further, as will be described below, the fiber end faces may be angled to improve the optical transmission characteristics (e.g., reflectance) of the optical connection.

Referring to fig. 1, the receptacle 20 and the plug 22 are shown separated with the protective dust cap 24 of the receptacle 20 and the protective pulling cap 26 of the plug 22 removed. A threaded coupling nut 28 on the plug 22 may be used to secure the plug 22 to the receptacle 20 when engaged, and may also be used to secure the pulling cap 26 during shipping and deployment of the drop cable. The pulling cap 26 defines a threaded portion 30 at a rear end thereof and a pulling ring 32 at a front end thereof. The pulling cap 26 provides protection for the optical connector of the plug 22 during shipping and deployment until the plug 22 and receptacle 20 are engaged. The pulling cap 26 may be secured to the drop cable 36 using a tether 34 so that the pulling cap 26 can be reused when the plug 22 is later separated from the receptacle 20. In a preferred embodiment, the pull ring 32 should be able to withstand cable pull forces of up to 600lbs. The pull ring 32 and pull cap 26 have a generally rounded front end to facilitate deployment through a conduit or pipe and over a pulley. Like the plug 22 of the assembly, the receptacle 20 is also covered and sealed during shipping and deployment with a threaded protective dust cap 24, the protective dust cap 24 being removed prior to insertion of the plug 22 into the receptacle 20. The dust cap 24 may similarly be secured to the receptacle 20 with a tether 34. At the end of the receptacle 20 opposite the dust cap 24, a pre-formed rubber sealing boot (not shown) may provide protection for the receptacle 20 from the environment in the connection terminal and, in some embodiments, also provide a sealing function. The protective sheath enables the assembly to be mounted in a breathable connection terminal or similar enclosure and is not required if the receptacle 20 is otherwise securely sealed from the environment.

Referring specifically to FIG. 2, the fiber optic plug 22 is mounted upon the end of a fiber optic drop cable 36 and is adapted to mate with a corresponding fiber optic receptacle 20. To secure the receptacle 20 and plug 22 together, the coupling nut 28 engages the threaded end of the receptacle 20. The manner in which the receptacle and plug assemblies are secured within the connector port through the external walls of the connection terminal will be described below. Fig. 3 is a cross-sectional view of the mated receptacle 20 and plug 22 of fig. 2 taken along line 3-3. The receptacle 20 includes, among other things, a one-piece housing 38, a ferrule retainer 40, a multi-fiber ferrule 42, guide pins (not shown), pin retaining clips (not shown), a ferrule boot 44, a spring centering cuff 46, a round spring 48, and a multi-point seal 50. The plug 22 includes an outer housing 52, a crimp band 54, a coupling nut 28, an alignment sleeve 56, and a plug sub-assembly 86, among other parts, the plug sub-assembly 86 including a crimp insert 58, an inner housing 60, a multi-fiber ferrule 43, a ferrule boot 44, a spring centering cuff 46, and a round spring 48. Details of the receptacle 20, plug 22 components and their subcomponents are described in detail below.

Referring specifically to fig. 4A, the fiber optic receptacle 20 includes a unitary receptacle housing 38 that may be used to mount within a connector port of a connection terminal or as a separate interconnect receptacle. The receptacle housing 38 houses a fiber optic ferrule assembly and is configured to align the ferrule assembly of the receptacle 20 with the fiber optic ferrule assembly of the corresponding fiber optic plug 22 such that they can be engaged in only one preferred orientation, as will be described in greater detail below with reference to FIG. 10. This feature is particularly advantageous for receptacle and plug assemblies that include multi-fiber ferrules, as well as for receptacle and plug assemblies that include Angled Physical Contact (APC) ferrules that require minimal angular offset between opposing ferrules. The receptacle housing 38 defines an internal cavity 62 that is open at opposite ends, a first end 64 and a second end 66. Typically, the opening at the first end 64 is large to receive a corresponding fiber optic plug 22. Conversely, the opening at the second end 66 is typically small and, in a preferred embodiment, is sized to be only slightly larger than the receptacle ferrule 42 so that the ferrule 42 can be inserted therethrough. The relatively large opening of the first end 64 enables cleaning with a cotton swab or a specialized cleaning tool. This has the advantage that the receptacle is exposed to adverse environmental conditions, such as dust, moisture and insect infestation, relative to the fiber optic plug when not in use for a long period of time. The first end 64 of this embodiment enables cleaning and better access without requiring disassembly.

The receptacle 20 in the exemplary embodiment shown and described includes, for example and without limitation, a multi-fiber receptacle ferrule 42 of the Mechanical Transfer (MT) variety. As best seen in FIG. 10, the ferrule 42 includes a single row of 12 optical fibers, however, any multi-fiber connector may be used in the practice of the present invention, including any number of optical fibers arranged in any manner. Although not included in this particular embodiment, the fiber optic receptacle 20 may include an alignment sleeve disposed within the internal cavity 62 defined by the receptacle housing 38. In all of the embodiments shown in FIGS. 1-10, the alignment sleeve is part of the plug 22 and is inserted into the internal cavity 62 by inserting the plug 22 into the receptacle 20. In this regard, the plug ferrule 43 is inserted into one end of the alignment sleeve, and the receptacle ferrule mounted upon the end of an optical fiber 88 terminated within a connection terminal (e.g., a direct connectorized optical fiber of a distribution cable or a tap for an optical fiber of a distribution cable) is inserted through the opening provided at the second end 66 of the receptacle 20 and into the other end of the alignment sleeve.

As shown, the receptacle housing 38 is cylindrical and defines a shoulder portion 68 disposed medially between the first end 64 and the second end 66. In a particularly preferred embodiment, the first end 64 of the receptacle housing 38 is inserted through the outer wall of the connection terminal from within the connection terminal until the radial face of the shoulder portion 68 facing the first end 64 abuts the inner surface of the wall. The retaining ring 70 is secured around the receptacle housing 38 against the outer surface of the wall, thereby retaining the wall between the retaining ring 70 and the shoulder portion 68 of the receptacle housing 38. By securing the shoulder 68 relative to the inner surface of the wall, such as relative to a nut, the relatively less noticeable receptacle 20 provides strain relief for cable pull forces up to about 600lbs. Preferably, a seal is provided between the shoulder portion 68 of the receptacle housing 38 and the inner surface of the wall using an O-ring, rubber ring, multi-point seal 50 (as shown), or other similar sealing means. The receptacle housing 38 is provided with an annular groove 72 between the shoulder portion 68 and the threaded portion for receiving the multi-point seal 50. Another annular groove 74 may be provided to receive the retaining ring 70. A key may be provided to be received in a correspondingly shaped recess formed in the inner surface of the wall, the key having the appearance of a flattened or partially square shape on the shoulder portion 68, thereby providing a mechanical feature to prevent rotation of the receptacle 20 within the connector port and ensuring that all of the receptacles 20 are mounted in the desired orientation.

The receptacle 20 also includes a biasing member assembly that includes a ferrule boot 44, a spring centering cuff 46, and a round coil spring 48. The ferrule retainer 40 serves to retain the receptacle ferrule 42 and the biasing member assembly within the interior cavity 62 of the receptacle housing 38. The biasing member assembly may be engaged with the receptacle ferrule 42 and the ferrule retainer 40 to urge the receptacle ferrule 42 toward the first end 64 of the receptacle housing 38. The biasing means of conventional multi-fiber connectors, such as existing MPO connectors and MT ferrule-based connectors, employ an oval spring to fit over the rear of the ferrule boot 44 while still allowing the 12-core fiber optic ribbon to pass through. An elliptical spring inherently has different stiffness in the x and y directions, which results in the introduction of off-axis forces and possible instability, as the spring typically does not exert its biasing force directly along the centerline of the shaft. Furthermore, round springs are produced with a smaller degree of deformation from part to part than non-round springs, in particular elliptical, oval, square or rectangular springs.

The off-center biasing force of the non-round spring causes the end face of the ferrule 42 to be angled relative to the radial plane of the receptacle housing 38 such that the optical fibers lead the radial plane on one side of the centerline and lag behind the radial plane on the opposite side. Thus, when the opposing receptacle and plug ferrules 42, 43 are mated, the angularity of the end faces causes the forwardmost optical fibers to make contact with the optical fibers of the opposing ferrule, even though the rearwardmost optical fibers have not yet made contact. As a result, either a pre-stressed torque force is introduced into the receptacle and plug assembly or at least some of the opposing optical fibers are in a non-contacting state. The round spring 48 of the present invention, in combination with the ferrule boot 44 and the spring centering cuff 46, can generate a centering biasing force against the rear of the receptacle ferrule 42. In other words, the round spring 48, the spring centering cuff 46 and the ferrule boot 44 provide for a centered force application regardless of whether the fiber optic ribbon is centered within the ferrule 42 or not, without modifying the design and construction of conventional multi-fiber ferrules. As used herein, the term "centralized force application" refers to the integration of all structural elements that cause the resultant biasing force exerted by the round coil spring 48 on the receptacle ferrule 42 (and/or the plug ferrule 43) to be exerted along the longitudinal axis defined by the receptacle housing 38. In a preferred embodiment, the biasing force of the round spring 48 is applied at the lateral center of the ferrule end face, more preferably between the two centermost fiber holes. Although not required, the cylindrical receptacle housing 38 facilitates the use of the round spring 48 in a compact and robust receptacle and plug assembly that significantly reduces any off-center component of the biasing force as compared to conventional multi-fiber ferrule-based (e.g., MT, MPO) assemblies.

The forward end of the round spring 48 is disposed against the rear of the spring centering cuff, which aligns the round spring 48 and transfers the spring force to the ferrule boot 44. The spring centering cuff 46 includes a bowl-shaped (i.e., generally concave) front surface that bears against a domed-shaped (i.e., generally convex) rear surface of the ferrule boot 44 to provide a centered force application to the lateral center of the end face of the ferrule 42. The rear surface of the ferrule boot 44 has a slightly smaller radius than the front surface of the centering cuff 46 such that the bowl-shaped surface of the centering cuff 46 fits over the entire domed-shaped surface of the ferrule boot 44. The less friction between the spring centering cuff 46 and the ferrule boot 44, the more centered the resultant biasing force is with respect to the optical fiber array. The ferrule boot 44 is preferably made of a rigid rubber, with optional low friction properties or post-processing, so that it will not deform under the pressure exerted by the spring 48 and can be inserted into the rear of the ferrule 42 without cracking. As a result, the ferrule boot 44 prevents epoxy from leaking between the ferrule boot 44 and the ferrule 42, and thus prevents contamination of the pin retainer clip 78. The rear end of the ferrule boot 44 defines a receiving window (funnel) for inserting the optical fibers 88 into the pre-assembled and discrete configurations. As previously mentioned, the rear of the ferrule boot 44 defines an arcuate surface having a theoretical focal point aligned with the lateral center of the end face of the ferrule 42. In this manner, the ferrule boot 44 simultaneously provides sealing, fiber guiding, and centering force application functions.

Referring to FIG. 4B, an alternative embodiment of the biasing member assembly of FIG. 4A is shown. In this embodiment, the domed-shaped surface of the ferrule boot 44 is replaced by a generally flat radial surface having a pair of ribs 126 projecting rearwardly therefrom and symmetrically splayed about 180 degrees. Preferably, the ribs 126 are aligned generally parallel to the transverse (i.e., height-wise) Y-axis of the ferrule 42, as shown in fig. 4B. The ribs 126 may be generally convex and have a curvature similar to the arcuate rear surface of the ferrule boot 44 previously shown in FIG. 4A, or may be flat and thus parallel and off the Y-axis of the ferrule 42. Furthermore, convex or flat ribs 126 may be provided elsewhere than the arcuate rear surface described previously. In a preferred embodiment, the convex ribs 126 are generally used with spring centering bands 46 having a generally concave front surface, while the flat ribs are generally used with spring centering bands 46 having a flat front surface.

For either rib shape or combination of ribs, the ribs 126 each serve to center the biasing force of the spring 48 along the Y-axis of the ferrule 42 while reducing or completely eliminating any biasing force along the X-axis of the ferrule 42 on either side of the Y-axis. As a result, the resultant biasing force does not generate a rotational moment about the Y-axis of the ferrule 42 that could result in an undesirable angular deflection of the end face of the ferrule 42. As previously discussed, a spring biasing force that is not centered along the longitudinal axis Z of the multi-fiber ferrule, or that is unbalanced about the longitudinal axis Z of the multi-fiber ferrule (or at least that is unbalanced about the Y-axis of the ferrule 42), will not consistently produce suitable physical contact between mating pairs of opposing optical fibers, thereby resulting in unacceptable optical characteristics of the receptacle and plug assembly. In contrast, conventional connectors having an oval spring that can exert different resultant biasing forces in its lateral directions (i.e., major and minor axes) will cause a rotational moment to be exerted on the end face of the ferrule 42, which results in the end face of the ferrule 42 having an angle with respect to a radial plane that is perpendicular to the longitudinal axis Z defined by the ferrule 42. If the end face of the ferrule 42 is rotated about the transverse axis Y, some of the mating optical fibers will lose physical contact with one another, thereby creating gaps between the optical fibers, resulting in back reflection and attenuation losses. In the present invention, the biasing member assembly used to center the resultant spring biasing force along the longitudinal axis Z defined by the ferrule 42 is preferably balanced about one or both of the lateral axes X, Y defined by the end face of the ferrule 42. The foregoing description of the ferrule boot 44, the spring centering cuff 46, and the round spring 48 centering the resultant spring biasing force on the receptacle ferrule 42 also pertains to the plug ferrule 43, and the components 44, 46, and 48 of the plug 22 may be configured the same as or different from the corresponding components 44, 46, and 48 of the receptacle 20.

Referring again to the embodiment of FIG. 4A, a pair of ferrule guide pins 76 are inserted into guide pin holes formed through the receptacle ferrule 42 and protrude a predetermined distance beyond the end face of the ferrule 42. The guide pin 76 is held in place by a pin retaining clip 78 that engages a circumferential groove 82 defined by the guide pin 76. In an alternative embodiment, the guide pins 76 are inserted into corresponding guide pin holes formed through the plug ferrule 43. The pin retaining clip 78 is optional and may be pre-assembled on the ferrule boot 44 to enable post-polishing insertion of the guide pin 76, if desired. The pin retention clip 78 is disposed about the front surface of the ferrule boot 44. As will be described in greater detail below, the alignment sleeve of the plug 22 serves to provide coarse alignment of the mating ferrules 42, 43, while the guide pins 76 serve to provide fine alignment of the mating ferrules, and in particular, the opposing optical fibers of the mating ferrules. Guide pin holes opening through the end face of the ferrule 42 are adapted to receive respective receptacle guide pins 76 to align the ferrule 42 with the opposing ferrule 43 in a manner well known to those skilled in the art and therefore need not be described in detail herein. In the exemplary embodiment shown, the multi-fiber ferrule 42 is an MT-type ferrule, and the body of the ferrule 42 defines at least one guide pin hole, and more typically a pair of guide pin holes for receiving respective guide pins 76.

Referring to fig. 5, a cross-sectional view of the receptacle 20 of fig. 4A taken along line 5-5 is shown in an assembled configuration with like parts indicated by like numerals. In addition to the foregoing structure, an O-ring 84 may be used to provide a seal between the protective dust cap 24 and the receptacle housing 38. As best seen in fig. 5, the multi-point seal 50 is retained in a groove 72 of the receptacle housing 38 and provides a plurality of sealing points between the receptacle housing 38 and, for example, the wall of the connection terminal.

The receptacle ferrule 42 is spring biased by the round spring 48, but is axially floatable within the interior cavity 62 of the receptacle housing 38 to thereby absorb compressive forces between the receptacle ferrule 42 and the opposing plug ferrule 43, which is preferably spring biased by the corresponding round spring 48. The round spring 48 is disposed against the front radial surface of the ferrule retainer 40 such that the spring 48 is slightly pre-stressed between the ferrule retainer 40 and the spring centering cuff 46. The ferrule retainer 40 may be secured to the receptacle housing 38 in any suitable manner, but in a preferred embodiment, the ferrule retainer 40 includes flexible hooks 78 that are received by features 80 (FIG. 4A) that protrude outwardly from the receptacle housing 38. The ferrule retainer 40 may be disengaged from the receptacle housing 38 to remove the receptacle ferrule 42, such as for cleaning, repair, replacement, or the like. The ferrule retainer 40 is designed so that it can be easily removed without the need for special tools. Once the receptacle ferrule 42 has been cleaned, repaired or replaced, the ferrule retainer 40 can be re-engaged with the receptacle housing 38.

Referring to fig. 6, the fiber optic plug 22 includes a plug sub-assembly 86, an alignment sleeve 56, a housing 52, a crimp band 54, and a coupling nut 26. The pulling cap 26 may be screwed onto the plug 22 with a coupling nut 28 during shipping and deployment. The cap 26 defines a pull ring 32, a threaded portion 30 for engagement with the coupling nut 28, and a tether 34 that is connectable to a drop cable 36 to retain the pull cap 26 and the plug 22 together. Or may be a molded plug boot (not shown) made of a flexible (silicone-type or other similar) material secured to the rear of the housing 52 and a portion of the drop cable 36 to seal the exposed portion of the drop cable 36 while substantially preventing kinking and providing bend strain relief for the cable 36 abutting the plug 22. The strength members 90 are terminated and the crimp band 54 is consolidated around the strength members 90. The pleated band 54 is preferably made of brass, but other suitable deformable materials may be used. Strength members (not shown) are cut flush with the strip of rear cable jacket thereby exposing GRP strength components 90 and a fiber optic ribbon comprising a plurality of ribbon-type optical fibers 94. The crimp band 54 provides strain relief for the cable 36. The plug sub-assembly 86 is assembled by first crimping the crimp band 54 around the rear wrap. The housing 52 and coupling nut 28 are threaded onto the cable 36 prior to the subassembly 86, as is well known to those of ordinary skill in the art. The housing 52 is then slid over the plug sub-assembly 86.

The alignment sleeve 56 defines a longitudinal passageway 98 for receiving the plug ferrules 43 and the receptacle ferrules 42 when the plug 22 is mated with the receptacle 20. As previously mentioned, the alignment sleeve 74 may be a component of the receptacle 20 or may also be a component of the plug 22. In the exemplary embodiment herein, the alignment sleeve 74 is a component of the plug 22. The housing 52 has a generally cylindrical shape with a forward first end 100 and a rearward second end 102. The outer housing 52 generally protects the plug sub-assembly 86 and, in the preferred embodiment, also aligns and engages the plug 22 with the mating receptacle 20. In addition, the housing 52 includes a through passage between the first and second ends 100 and 102. The passage of the housing 52 includes alignment and keying features such that the plug subassembly 86 cannot rotate once the plug 22 is assembled. The first end 100 of the outer housing 52 includes a key slot (see reference numeral 104 in fig. 1 and 10) for aligning the plug 22 with the receptacle 20 and thereby aligning the plug sub-assembly 86 with respect to the receptacle 20. Thus, the plug 22 and corresponding receptacle 20 are configured to mate in only one orientation. In a preferred embodiment, the orientation may be marked on the receptacle 20 and the plug 22 with alignment indicia so that a less skilled field technician can readily mate the plug 22 with the receptacle 20. Any suitable marking indicia may be employed. After alignment, the field technician engages the internal threads of the coupling nut 28 with the external threads of the receptacle 20 to secure the plug 22 to the receptacle 20.

The housing 52 of the plug 22 may further define a shoulder 106, the shoulder 106 serving as a mechanical stop for the conventional rubber O-ring 96 against its front radial surface and the coupling nut 28 against its rear radial surface. The O-ring 96 provides an environmental seal when the coupling nut 28 is engaged with the threaded portion of the receptacle housing 38. The coupling nut 28 has a channel sized to loosely fit the second end 102 and the shoulder 106 of the housing 52 such that the coupling nut 28 can easily rotate about the housing 52. In other words, the coupling nut 28 cannot move in the direction of the receptacle 20 beyond the shoulder 106, but is free to rotate relative to the housing 52. Figure 7 is a cross-sectional view of the plug 22 taken along line 7-7 of figure 6 and showing the assembled structure, with like parts being given like reference numerals.

Referring to fig. 8, the plug sub-assembly 86 is shown. As previously described, the plug subassembly 86 includes the multi-fiber ferrule 43, the ferrule boot 44, the spring centering cuff 46, the round spring 48, the crimp insert 58, and the inner housing 60. The plug ferrule 43 is at least partially disposed within the inner housing 60, extends longitudinally therefrom and projects outwardly into the alignment sleeve 56. The plug ferrule 43 is mounted within the inner housing 60 such that the end face of the plug ferrule 43 extends slightly beyond the front end of the inner housing 60. Similar to the fiber optic receptacle 20, the fiber optic plug 22 includes a corresponding multi-fiber ferrule 43, preferably of identical construction, and the plug 22 of the illustrated exemplary embodiment includes a single 12-core MT-type ferrule 43. The plug sub-assembly 86 may also include a rubber O-ring 108 disposed within a groove 110 defined by the crimp insert 58. The O-ring 108 is used to provide a seal between the pleated insert 56 and the plug housing 52 when the coupling nut 28 engages the threaded portion of the protective pull cap 26 or the receptacle 20.

As previously described with respect to the receptacle 20, the plug 22 also includes a biasing member assembly that includes a round spring 48, a spring centering cuff 46 and a ferrule boot 44. The biasing member assembly may engage the plug ferrule 43 and a radial surface provided on the forward end of the crimp insert 58 to urge the plug ferrule 43 toward the first end 100 of the housing 52. The round spring 48, in conjunction with the ferrule boot 44 and the spring centering cuff 46, operate in the manner previously described to exert a spring biasing force that is centered on the end face of the plug ferrule 43. In a preferred embodiment, the biasing force of the spring 48 is exerted on the end face of the ferrule 43 along a longitudinal axis defined by the plug 22, or balanced about one or more transverse axes defined by the end face of the plug ferrule 43, such that the resultant biasing force urges the plane defined by the ferrule end face to be generally perpendicular to the longitudinal axis defined by the plug 22. The forward end of the round spring 48 is disposed against the rear of the spring centering cuff 46, which aligns the round spring 48 and couples the spring force to the ferrule boot 44.

The spring centering boot 46 includes a bowl-shaped (i.e., concave) front surface that bears against a domed-shaped (i.e., convex) rear surface on the ferrule boot 44 to provide a centering force application to the lateral center of the end face of the ferrule 43. The rear surface of the ferrule boot 44 has a slightly smaller radius than the front surface of the centering cuff 46 such that the bowl-shaped surface of the centering cuff 46 fits over the entire arcuate surface of the ferrule boot 44. The less friction between the spring centering cuff 46 and the ferrule boot 44, the more centered the resultant biasing force is with respect to the optical fiber array. The ferrule boot 44 is preferably made of a rigid rubber, optionally with low friction or post-treatment, so that it will not deform under the pressure exerted by the spring 48 and can be inserted into the rear of the ferrule 43 without cracking. The rubber material also provides a slight interference fit to seal the rear of the ferrule 43. Thus, the ferrule boot 44 serves to prevent epoxy from leaking between the ferrule boot 44 and the plug ferrule 43. The rear end of the ferrule boot 44 defines a receiving window (funnel) for inserting the optical fibers 94 into the pre-assembled and discrete configuration. As previously mentioned, the rear of the ferrule boot 44 defines an arcuate surface having a theoretical focal point aligned with the lateral center of the end face of the ferrule 43. In this manner, the ferrule boot 44 simultaneously provides sealing, fiber guiding, and centering force application functions.

The plug ferrules 43 are resiliently biased by the round springs 48, but are capable of floating axially within the inner housing 60 and the alignment sleeve 56 to absorb compressive forces between the plug ferrules 43 and the opposing receptacle ferrules 42, which receptacle ferrules 42 are preferably resiliently biased by the corresponding round springs 48. The round spring 48 is disposed against the front radial surface of the pleated insert 58 such that the spring 48 is slightly pre-compressed between the pleated insert 58 and the spring centering cuff 46. As previously discussed, the spring centering cuff 46 is disposed against the bearing surface of the ferrule boot 44 to center the resultant spring biasing force on the center of the end face of the plug ferrule 43. The rear of the ferrule boot 44 defines a receiving window (funnel) for guiding the optical fibers 94 into the ferrule boot 44 and the plug ferrule 43. Fig. 9 is a cross-sectional view of the plug sub-assembly 86 of fig. 8 taken along line 9-9, showing the assembled configuration, with like parts indicated by like numerals.

Referring to fig. 10, a schematic end view of the receptacle 20 and plug 22 of fig. 1 is shown disassembled to illustrate alignment and insertion features of the assembly. As previously discussed, the plug 22 engages the receptacle 20 to optically connect the optical fibers of the plug ferrule 43 with the corresponding receptacle ferrule 42. The alignment sleeve 56 is retained and disposed within the outer housing 52 of the plug 22 such that the key slot 114 of the alignment sleeve 56 is aligned with the key slot 104 defined by the plug outer housing 52. In the preferred embodiment, the plug housing 52 defines a pair of openings 116 along its length adjacent the first end 100 for receiving features 118 defined by the alignment sleeve 56. The shape feature 118 is received by the opening 116 to properly align the alignment sleeve 56 within the plug housing 52 to align the key slot 114 of the alignment sleeve 56 with the key slot 104 of the outer shell 52.

To achieve the optical connection, the plug 22 is inserted into the receptacle 20, and the receptacle 20 may receive only a plug 22 having the same ferrule configuration. The receptacle 20 defines a first key 120, the first key 120 being received in the key slot 104 of the plug housing 52 and the key slot 114 of the alignment sleeve 56. As shown, the key 120 is a convex shaped feature molded into the receptacle housing 36 of the receptacle 20. For each type of multi-fiber receptacle ferrule 42 and plug ferrule 43 pair, receptacles having a particular keying shape may be manufactured. Although a common housing 52 may be used for all ferrule types, an alignment sleeve having a particular key shape may be inserted into the housing 52 to accommodate a particular ferrule. The receptacle 20 also defines a second projecting shape feature 122 that excludes the non-conforming alignment sleeve 56 to prevent a different plug ferrule 43 from being inserted into the receptacle 20 and mated with the receptacle ferrule 42. As shown, the alignment sleeve 56 of the plug 22 defines an opening 124 for receiving the second protruding form feature 122 (also referred to herein as the "excluding form feature 122"). The key 120 and the rejection features 122 prevent rotation of the housing 52 relative to the receptacle housing 38 of the receptacle 20 when the guide pins 76 align the receptacle and plug ferrules 42, 43. Because the alignment and keying features extend toward the vicinity of the end of the plug 22, a plug 22 having a ferrule configuration different than the receptacle 20 is prevented from being inserted into the receptacle 20 until the receptacle ferrule 42 and the plug ferrule 43 make physical contact, thereby eliminating potential damage to the end face. Proper alignment when mating multiple optical fibers is also important to ensure optimal optical transmission characteristics between the opposing pairs of optical fibers 88, 94.

In an alternative embodiment, the threads of the coupling nut 28 and receptacle housing 38 may be replaced with a bayonet or push-pull mechanism to secure the plug 22 within the receptacle 20. Alternatively, a spring clip or similar device may be added to engage the plug 22 with the receptacle 20 to secure them together. The seal may be removed or loosened depending on the extent to which the assembly is exposed to the adverse environment. The optional plug jacket may be pre-manufactured and fitted to the crimp insert 58 and drop cable 36 or may be overmolded (overmolded) using techniques provided by Corning cable systems LLC of Hickory North Carolina. In addition, heat shrinkable tubing can be used to accomplish the same goal as the sheath when the appearance is less important and the bending properties are less severe. As previously described, the alignment sleeve 56 may be integrated into the receptacle 20 while retaining the same assembly technique and allowing for easy removal and cleaning of the receptacle ferrule 42.

The design of many types of multi-fiber ferrules can be derived from the basic design shown and described herein. Multi-fiber ferrule designs driven by available space and requirements are possible. Additional strain relief members may be added to the receptacle 20 if desired. The crimping scheme may vary depending on the drop cable type and requirements. If the drop cable does not include the dual GRP dielectric strength members as shown, the means of attaching the strength members to the plug body may include gluing or other securing means, such as clamping.

The described embodiments provide advantages over conventional multi-fiber optic receptacle and plug assemblies. For example, the compact size of the embodiments described herein enables an FFTx drop cable to have a 38mm diameter package and enables multiple receptacles to be installed into a connection terminal or other enclosure, while requiring very little penetration depth of the receptacle into the terminal or package. The alignment and keying features of these components enable them to be fully APC-type, while the unique fit prevents the components from being misassembled during production and installation. By locating the alignment sleeve 56 within the plug 22 relative to the receptacle 20, the receptacle volume is reduced and components of the receptacle 20 that are exposed to adverse environmental conditions for extended periods of time can be easily accessed and cleaned. The over-molded boot eliminates the need for heat shrink tubing and also improves the sealing integrity of the assembly under adverse conditions, wherein the pre-formed boot can be removed from the plug 22.

In the various embodiments described above, the present invention provides multi-fiber receptacle and plug assemblies that include identical multi-fiber optic connectors, such as connectors of the MT or MPO type technologies. The rigid shoulder 68 of the receptacle 20 is disposed against the inner surface of the terminal wall to provide the best retention of external pulling forces as compared to conventional threaded designs that use nuts on the inside of the wall to secure the receptacle 20. The fiber optic receptacle 20 and plug 22 assembly of the present invention provides a sealed design that prevents moisture and contaminants from entering the end face of the ferrule. In all embodiments, the O-rings provide static seals that are positioned in combination with the form factor to minimize vacuum build-up when the plug 22 is removed from the receptacle 20 and to minimize pressure build-up when the plug 22 is inserted into the receptacle 20. In general, most of the components of the receptacle 20 and plug 22 are made of a suitable polymer. Preferably, the polymer is a UV stabilized polymer such as ULTEM2210 available from GE plastics, Inc., although other suitable materials may be used. For example, stainless steel or other suitable metals and plastics may also be used.

It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (19)

1. A multi-fiber optic receptacle adapted to engage a complementary plug, the receptacle comprising:

a receptacle housing having an aperture formed therein, the aperture defining an interior cavity adapted to receive the complementary plug; and

a receptacle multi-fiber ferrule extending into said interior cavity of said receptacle housing;

wherein the interior cavity of the receptacle housing defines axially projecting tabs and axially projecting rejection members disposed directly above and below the receptacle multi-fiber ferrule, respectively, and the rejection members are isolated from the sidewalls of the interior cavity, and the receptacle includes a ferrule boot, a spring centering cuff, and a ferrule retainer secured to the receptacle housing.

2. The multi-fiber optic receptacle of claim 1, wherein the repelling member is a protrusion integrally formed with the receptacle housing.

3. The multi-fiber optic receptacle of claim 1, wherein the receptacle is externally threaded.

4. A multi-fiber optical fiber assembly comprising:

the receptacle of claim 1;

a plug for engaging the receptacle, the plug having a plug housing, an alignment sleeve, and a plug multi-fiber ferrule, wherein the plug housing and the alignment sleeve of the plug each have a key slot that is aligned and adapted to receive the key of the receptacle during mating.

5. The multi-fiber optical fiber assembly of claim 4, wherein the plug housing includes a plurality of openings for positioning the alignment sleeve thereon.

6. The multi-fiber optic assembly of claim 4, wherein said receptacle and said plug are cylindrical in cross-section.

7. The multi-fiber optic assembly of claim 4, wherein the plug multi-fiber ferrule is part of a plug sub-assembly, the plug sub-assembly further comprising a ferrule boot, a spring centering cuff, a round spring, a pleated insert, and an inner housing; and wherein the plug multi-fiber ferrule is at least partially disposed within the inner housing, extends longitudinally therefrom and projects outwardly to the alignment sleeve.

8. The multi-fiber optic receptacle of claim 1, further comprising a pair of ferrule guide pins positioned by the pin retention clips onto said receptacle multi-fiber ferrule.

9. A fiber optic assembly for optically connecting a plurality of optical fibers, comprising:

a plug comprising a plug housing defining an internal cavity, the housing having at least one plug multi-fiber ferrule therein, and the plug comprising an alignment sleeve retained and disposed in the plug housing, the alignment sleeve having a keyway and an opening, the keyway and the opening being located directly above and below the plug multi-fiber ferrule, respectively;

a socket for receiving the plug, the socket comprising: a receptacle housing defining an interior cavity having at least one receptacle multi-fiber ferrule therein and further defining axially raised keying and axially raised rejection members disposed directly above and below the receptacle multi-fiber ferrule, respectively, such that when the at least one receptacle and the at least one plug are mated together, the rejection members and the keying are received within the first and second clearance openings of the plug, respectively, wherein the receptacle further comprises a ferrule boot, a spring centering cuff, and a ferrule retainer secured to the receptacle housing.

10. The fiber optic assembly of claim 9, wherein the receptacle is externally threaded and the plug further includes an internally threaded coupling nut for threadably engaging the external threads of the receptacle.

11. The fiber optic assembly of claim 9, wherein the plug multi-fiber ferrule is part of a plug sub-assembly, the plug sub-assembly further comprising a ferrule boot, a spring centering cuff, a round spring, a crimped insert, and an inner housing; and wherein the plug multi-fiber ferrule is at least partially disposed within the inner housing, extends longitudinally therefrom and projects outwardly to the alignment sleeve.

12. The fiber optic assembly of claim 9, wherein the receptacle and plug are cylindrical in cross-section.

13. The fiber optic assembly of claim 9, wherein the receptacle and the plug further comprise a round spring.

14. The fiber optic assembly of claim 13, wherein the round spring of each of the receptacle and the plug concentrates spring force on the end faces of the plug multi-fiber ferrule and the receptacle multi-fiber ferrule.

15. A multi-fiber optic plug adapted to engage a complementary receptacle, comprising:

a plug housing defining a first end, a second end, and an interior cavity;

a plug multi-fiber ferrule disposed within the plug housing; and

an alignment sleeve retained and disposed within the plug housing, the alignment sleeve having a keyway and an opening, the keyway and the opening being positioned directly above and below the plug multi-fiber ferrule, respectively, to provide clearance for the raised exclusion member and the key of a complementary receptacle when the plug is engaged with the receptacle, wherein the receptacle housing includes a plurality of openings for positioning the alignment sleeve therein.

16. The multi-fiber optical fiber plug of claim 15, further comprising an internally threaded coupling nut adapted to threadably engage the external threads of the complementary receptacle.

17. The multi-fiber optic receptacle of claim 15, wherein said plug housing defines a key slot adapted to receive a key of said complementary receptacle.

18. The multi-fiber optic receptacle of claim 15, wherein the plug multi-fiber ferrule is part of a plug sub-assembly, the plug sub-assembly further comprising a ferrule boot, a spring centering cuff, a round spring, a pleated insert, and an inner housing; and wherein the plug multi-fiber ferrule is at least partially disposed within the inner housing, extends longitudinally therefrom and projects outwardly to the alignment sleeve.

19. A multi-fiber optical fiber assembly comprising:

the plug of claim 15;

a receptacle connected to the plug, wherein the receptacle includes a receptacle multi-fiber ferrule, a ferrule boot, a spring centering cuff, and a ferrule retainer secured to the receptacle housing.