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WO1996004580A1 - Attenuateur optique a surface partiellement reflechissante - Google Patents

Attenuateur optique a surface partiellement reflechissante Download PDF

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Publication number
WO1996004580A1
WO1996004580A1 PCT/US1995/009297 US9509297W WO9604580A1 WO 1996004580 A1 WO1996004580 A1 WO 1996004580A1 US 9509297 W US9509297 W US 9509297W WO 9604580 A1 WO9604580 A1 WO 9604580A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical
fiber
optical fibers
endface
attenuator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1995/009297
Other languages
English (en)
Inventor
Warren H. Lewis
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Whitaker LLC
Original Assignee
Whitaker LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Whitaker LLC filed Critical Whitaker LLC
Publication of WO1996004580A1 publication Critical patent/WO1996004580A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
    • G02B6/29361—Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
    • G02B6/29368—Light guide comprising the filter, e.g. filter deposited on a fibre end
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting
    • G02B6/266—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting the optical element being an attenuator
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/36—Mechanical coupling means
    • G02B6/38—Mechanical coupling means having fibre to fibre mating means
    • G02B6/3807—Dismountable connectors, i.e. comprising plugs
    • G02B6/381—Dismountable connectors, i.e. comprising plugs of the ferrule type, e.g. fibre ends embedded in ferrules, connecting a pair of fibres
    • G02B6/3818—Dismountable connectors, i.e. comprising plugs of the ferrule type, e.g. fibre ends embedded in ferrules, connecting a pair of fibres of a low-reflection-loss type
    • G02B6/3822—Dismountable connectors, i.e. comprising plugs of the ferrule type, e.g. fibre ends embedded in ferrules, connecting a pair of fibres of a low-reflection-loss type with beveled fibre ends
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/36—Mechanical coupling means
    • G02B6/38—Mechanical coupling means having fibre to fibre mating means
    • G02B6/3807—Dismountable connectors, i.e. comprising plugs
    • G02B6/3833—Details of mounting fibres in ferrules; Assembly methods; Manufacture
    • G02B6/3847—Details of mounting fibres in ferrules; Assembly methods; Manufacture with means preventing fibre end damage, e.g. recessed fibre surfaces
    • G02B6/3849—Details of mounting fibres in ferrules; Assembly methods; Manufacture with means preventing fibre end damage, e.g. recessed fibre surfaces using mechanical protective elements, e.g. caps, hoods, sealing membranes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/36—Mechanical coupling means
    • G02B6/38—Mechanical coupling means having fibre to fibre mating means
    • G02B6/3807—Dismountable connectors, i.e. comprising plugs
    • G02B6/3833—Details of mounting fibres in ferrules; Assembly methods; Manufacture
    • G02B6/3854—Ferrules characterised by materials

Definitions

  • the present invention relates generally to fiber optic devices. Specifically, the present invention relates to a fiber optic fixed attenuator.
  • U.S. Patent Nos. 4,557,556, 4,557,557, and 5,285,516 disclose methods of fabricating attenuators for optical fibers by fusion splicing. In each of these methods, a fiber is cleaved, the cleaved ends are brought into a desired relationship, and the ends are melted or fused together to provide the desired structure. During fabrication, light is injected by a transmitter into one of the fibers and received by a receiver coupled to the other fiber. When the fibers are being fused, the power level is monitored and relative movement of the fiber ends is effected to achieve a desired observed level of optical loss.
  • the axes of the cleaved ends are offset and butted against one another.
  • the abutted offset ends of the fibers are melted and the axes of the cores of the melted abutted fiber ends are aligned by way of surface tension. This realigns the cores, except that the cleaved ends of the cores bend off the axis in opposite directions.
  • the cleaved fiber ends are aligned and melted, and while the ends are in a plastic state, they are moved towards each other to distort the fiber ends.
  • the cores bend slightly near their abutted ends and are partially or wholly misaligned to provide the attenuation.
  • U.S. Patent No. 5,257,335 discloses a fixed attenuator wherein an attenuating (absorbing) membrane is sandwiched between the obliquely polished ends of a pair of fiber segments. This arrangement is presumably effective for its intended purpose, but the use of an attenuating membrane is subject to the possibility that at high optical power levels, the membrane could overheat and be damaged.
  • a further disadvantage suffered by the above described technologies is the dependency of the attenuation level on the application for which the respective attenuators are used.
  • an attenuator might be used in three different configurations. First, an attenuator could be interposed between a light source and an output fiber. Second, an attenuator could be interposed between an input fiber and a detector. Finally, an attenuator could be interposed between an input fiber and an output fiber.
  • the attenuators described in the above-referenced patents yield different attenuation values. This is due to the fact that these attenuators transfer light from the fiber core into the cladding in the direction of propagation.
  • an optical attenuator which may be inexpensively produced and which may provide a precise attenuation of light energy over a broad range, and for different configurations.
  • an optical attenuator which is capable of being fabricated to provide any desired level of attenuation within a wide range of levels, and which is characterized by a high level of wavelength insensitivity.
  • an optical attenuator according to the present invention uses a partially reflecting layer interposed in the optical path. The layer is inclined relative to the fiber axis so that the light traveling along the axis is reflected into the fiber's cladding and does not propagate back down the fiber to the source. This avoids the inconsistencies of previous attenuators which transfer light forward into the cladding.
  • attenuators designed according to the present invention attenuation is constant whether light is being transmitted into a fiber or a detector.
  • an optical attenuator having first and second optical fibers, each of which has a core axis, a cladding substantially concentric with the core axis, and a substantially planar endface having a normal vector at a common fixed angle to the core axis.
  • the optical attenuator also includes a partially reflective coating on the endface of at least one of the optical fibers. The partially reflective coating is for reflecting electromagnetic energy transmitted in the direction of the core axes into the cladding of one of the optical fibers.
  • the attenuator includes two assemblies, each having an optical fiber coaxially fixed within a cylindrical ferrule. Each assembly has a planar endface having a normal vector at a common fixed angle to the fiber axis, with the ferrule endface and its associated optical fiber endface being substantially coplanar.
  • the two assemblies are held in a fixed relationship with respect to each other with the endfaces being substantially parallel to each other and the fiber cores substantially collinear as described above. For the present invention to operate properly, the endfaces of the optical fibers need not be in physical contact.
  • the attenuator of the present invention operates even with an air gap between the endfaces.
  • the partially reflecting coating may be applied to one or both of the fiber endfaces.
  • the coating is preferably largely wavelength insensitive in the relevant range.
  • the fixed angle is preferably large enough so that the portion of the light that is not transmitted is reflected outside the fiber's acceptance cone, but small enough so that the amount of light reflected does not depend significantly on the polarization of the incident light.
  • Angles in the range of 8 to 12 degrees with respect to the normal to the ferrule endface are appropriate for normal single-mode fiber.
  • Angles for multi-mode fibers may be chosen from a broader range because the reflection of light back to the source is not generally of concern.
  • the attenuator according to the present invention may be fabricated as follows. First and second ferrules having the desired endface angle are provided. Respective first and second optical fibers are inserted with their ends protruding slightly past the ferrule endfaces. The fibers are then fixed in place and the fiber endfaces are polished so that they are substantially coplanar with their respective ferrules' endfaces. In one embodiment, the partially reflecting coating is applied to one of the fiber endfaces. In another embodiment, the partially reflective coating is applied to both of the fiber endfaces. The assemblies are then registered to each other so that the fiber endfaces are substantially parallel to each other with the fiber cores being substantially collinear. Alignment may be effected by providing a sleeve that accommodates the assemblies and cementing the assemblies into the sleeve when the desired optical contact is achieved.
  • Fig. 1 is a representation of an optical attenuator assembly according to a particular embodiment of the present invention
  • Fig. 2 is a representation of a ferrule assembly employed by a particular embodiment of the present invention
  • Fig. 3 is a longitudinal cross-section of an attenuator assembly according to a particular embodiment of the invention
  • Fig. 4 is a magnified view of a portion of the cross-section of Fig. 3 according to one embodiment
  • Fig. 5 is a magnified view of a portion of Fig. 4 showing the path of transmitted light
  • Fig. 6 is a magnified view of a portion of the cross-section of Fig. 3 according to another embodiment
  • Fig. 7 is a magnified view of a portion of Fig. 6 showing the path of transmitted light
  • Fig. 8 is magnified view of a portion of the cross- section of Fig. 3 according to a further embodiment of the invention.
  • Fig. 9 is a magnified view of a portion of Fig. 8 showing the path of transmitted light
  • Figs. 10 and 11 show the present invention packaged for use with industry standard FC type optical fiber connectors
  • Figs. 12 and 13 show the present invention packaged for use with industry standard SC type optical fiber connectors.
  • Fig. l is a representation of the operative portion of an optical attenuator assembly 10 designed according to a embodiment of the present invention.
  • Assembly 10 includes two ferrule assemblies 12 and 14 having central bores which contain optical fiber segments 16 and 18, respectively.
  • Ferrule assemblies 12 and 14 are held together in a fixed relationship at an interface 20 inside an alignment sleeve 22, assembly 10 having mating faces 13 and 15 for optically mating fiber end faces 17 and 19 to other optical assemblies (not shown) .
  • Sleeve 22 may be a split sleeve as shown in Fig. 1 exerting radial pressure on both ferrules, thereby centering and aligning them.
  • Each ferrule assembly is similarly constructed and may be described with reference to ferrule assembly 12 as shown in Fig. 2.
  • the corresponding reference numbers for ferrule 14 are shown in parentheses.
  • Ferrule assembly 12 (14) is a length of capillary tubing having a central bore sized to accommodate optical fiber 16 (18) .
  • the capillary tubing of ferrule assembly 12 (14) is typically constructed from ceramic, alumina, zirconia, or stainless steel.
  • Optical fiber 16 (18) may be either single-mode or multi-mode fiber.
  • a single-mode fiber typically has a core diameter of 8.3-10 ⁇ m, a cladding diameter of 125 ⁇ m, and a buffer diameter of 250, 500, or 900 ⁇ m.
  • Single-mode fibers typically operate at wavelengths between 1200 and 1600 nm.
  • Multi-mode fibers with cladding diameters of 125 ⁇ m are available with core diameters of 50, 62, and 100 ⁇ m.
  • Multi- mode fibers are also available with a core diameter of 100 ⁇ m and a cladding diameter of 140 ⁇ m.
  • Multi-mode fibers typically operate at wavelengths between 700 and 1600 nm.
  • ferrule assemblies 12 and 14 are not constrained by any particular fiber dimension, and may be, for example, on the order of 1.0-2.5 mm.
  • One end of ferrule assembly 12 (14) is formed with an endface 24 (25) having a normal 26 (27) that is inclined from central bore axis 28 (29) by a desired fixed angle ⁇ . In specific embodiments, the angle ranges between 8 and 12 degrees.
  • Ferrule assembly 12 (14) is fabricated as follows.
  • Optical fiber segment 16 (18) is cemented in the central bore of ferrule assembly 12 (14) .
  • the end of fiber segment 16 (18) protrudes a short distance beyond the ferrule assembly's inclined endface 24 (25) .
  • the protruding end of fiber 16 (18) is ground to approximately the angle of ferrule endface 24 (25) , and then polished so that endface of fiber 16 (18) is substantially coplanar with ferrule endface 24 (25) .
  • a partially reflecting coating may then be applied to the ferrule and fiber endfaces.
  • ferrule assembly 14 is fabricated in a similar manner, although the endface of ferrule assembly 14 may or may not be coated with a partially reflective coating according to various embodiments, some of which are described below with reference to Figs. 3-9.
  • Fig. 3 shows a longitudinal cross-section of an attenuator assembly 10 designed according to a particular embodiment of the invention.
  • attenuator assembly 10 is fabricated by aligning two ferrule assemblies 12 and 14 within alignment sleeve 22 so that fiber segments 16 and 18 have their endfaces in substantial optical contact, and the central axes of fiber segments 16 and 18 are substantially collinear.
  • Several different embodiments of attenuator assembly 10 of Fig. 3 are possible, some of which are described below.
  • Fig. 4 is a magnified view of region A of Fig. 3 according to one embodiment of the invention. According to this embodiment, only the endfaces of ferrule assembly 12 and optical fiber 16 are coated with a partially reflective coating 30. Ferrule assemblies 12 and 14 are fixed together within sleeve 22 by means of epoxy 32. It will be understood that ferrule assemblies 12 and 14 may be coupled by a variety of means other than epoxy 32.
  • Fig. 5 is a magnified view of region B from Fig. 4 and shows the optical path 34 of a light beam traveling down the optical fiber cores 36 and 38 of fiber segments 16 and 18, respectively. As described above, a portion of the light beam reflects from partially reflective coating 30 and into the cladding 40 of optical fiber 16 along path 42 which forms the angle with path 34.
  • the angle ⁇ is chosen so that the light that is reflected by coating 30 enters cladding 40 and does not propagate back toward the source of the light beam.
  • the minimum value for the angle of inclination i.e., a
  • the angle ⁇ should be large enough so that the portion of the light that is not transmitted partially reflective coating 30 is reflected outside the fiber's acceptance cone. Angles in the range of 8 to 12 degrees are appropriate for normal single-mode fiber.
  • the angle that will just prevent the reflected light from reentering the fiber core is given by sin -1 (NA/n) where NA is the numerical aperture in air of the fiber and n is the refractive index of the fiber core.
  • the minimum angle is about 10 degrees.
  • the angle ⁇ must also be small enough so that the amount of light reflected does not depend significantly on the polarization of the incident light, at least where it is desired to have the attenuation independent of polarization. In such a case, the angle should be as small as possible, that is, only slightly larger than the minimum value. Angles for multi-mode fibers may be chosen from a broader range because the reflection of light back to the source is not generally of concern.
  • Coating 30 may be metallic or a multi-layer dielectric coating. It is normally possible to have the coating reflectivity reasonably independent of wavelength for the range of operating wavelengths. As mentioned above, such coatings may be obtained from Evaporated Coatings Inc. Another source is Coherent Optical, Inc. The invention may also employ an epoxy such as Epo-
  • Tek 314 epoxy as epoxy 32 to hold ferrule assemblies 12 and 14 together. This same epoxy may be used to fix the optical fiber in the capillary bore.
  • the 314 epoxy has the benefit of having an optical index of 1.49, which most nearly matches the optical index 1.46 of the glass fiber used in this embodiment while maintaining a strong and rugged bonding capability. This index match minimizes changes in optical index along the optical path of the device which degrade optical performance.
  • Fig. 6 is a magnified view of region A of Fig. 3 according to another embodiment of the invention.
  • attenuator assembly 10 has partially reflective coatings 30 and 52 on ferrule assemblies 12 and 14, respectively. The partially reflective coatings are separated by epoxy 32.
  • this attenuator assembly attenuates light traveling in both directions down optical fibers 16 and 18.
  • One advantage derived from having a coating on both ferrule assemblies is that a smaller inventory of ferrule assemblies may be maintained for the manufacturing of a given number of attenuators having a wide variety of attenuation levels. For example, if only one ferrule assembly were coated in each assembly, one would need to coat ferrule assemblies differently for each desired level of attenuation.
  • a 15 dB attenuator may be constructed without having to maintain an inventory with individual 15 dB ferrule assemblies.
  • Fig. 7 is a magnified view of region C from Fig. 6 and shows paths 54 and 56 of two light beams traveling in opposite directions. As with the embodiment described above, a portion of each light beam is reflected from coatings 30 and 52 into cladding 40 and 58 along reflection paths 60 and 62, respectively. Reflection paths 60 and 62 form the angle ⁇ with optical paths 54 and 56, respectively. As with the above-described embodiment, the angles ⁇ may range from 8 to 12 degrees.
  • Coating 52 may be of the same material as coating 30, which may be the same as coating 30 of Figs. 4 and 5.
  • Fig. 8 is another magnified view of region A of Fig. 3 according to a further embodiment of the invention.
  • attenuator assembly 10 has a partially reflective coating 30 (similar to coating 30 of Figs. 4 and 5) on ferrule assembly 12, a layer of epoxy 32, and an anti-reflective coating 72 on ferrule assembly 14.
  • anti-reflective coating 72 may comprise, for example, magnesium flouride (MgF 2 ) •
  • Anti-reflective coating 72 reduces undesirable reflection from the endface of optical fiber 18, as well as reduces interference effects which result from gaps between the fiber endfaces. Such gaps may result from the polishing of the ferrule endfaces which may cause the fiber endfaces to be concave.
  • FIG. 9 is a magnified view of region D from Fig. 8 and shows the optical path 74 of a light beam traveling down the optical fiber cores 36 and 38 of fiber segments 16 and 18, respectively. As with the embodiment of Figs. 4 and 5, a portion of the light beam is reflected from partially reflective coating 30 at an angle ⁇ along reflective path 76. Substantially all of the remaining light continues traveling along path 74, through epoxy 32, anti-reflective coating 72, and into core 38 of fiber 18.
  • Figs. 10 and 11 show the present invention packaged for use with industry standard FC type optical fiber connectors. Fig.
  • FIG. 10 shows a 2.5 mm threaded attenuator package 80 with dust caps 82 protecting connector mating interfaces 84 and 86.
  • Fig. 11 shows a cross-section of attenuator package 80 in which attenuator 10 is shown. Figs.
  • FIG. 12 and 13 show the present invention packaged for use with industry standard SC type optical fiber connectors.
  • Fig. 12 shows a 3.25 mm attenuator package 90 with dust caps 92.
  • Fig. 13 shows a cross-section of attenuator package 90 in which attenuator 10 is shown adapted for mating with conventional fiber optic connectors.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

Un atténuateur optique (10) comporte une couche partiellement réfléchissante (30) interposée dans la voie optique. La couche est inclinée par rapport à l'axe de la fibre de sorte que la lumière se déplaçant le long de l'axe soit réfléchie dans le gainage (40) de la fibre et ne se repropage pas de la fibre vers la source. Dans un mode de réalisation spécifique, un atténuateur optique comporte des première et seconde fibres optiques, chacune ayant un axe central, un gainage sensiblement concentrique à l'axe central, et une face terminale sensiblement plane au niveau d'un angle fixe commun par rapport à l'axe central. L'atténuateur optique (10) comporte également un revêtement partiellement réfléchissant sur la face terminale d'au moins une des fibres optiques (16, 18). Le revêtement partiellement réfléchissant (30) est prévu pour réfléchir une énergie électromagnétique transmise en direction des axes centraux dans le gainage (40) d'une des fibres optiques. Les première et seconde fibres optiques (16, 18) sont maintenues dans une relation fixe l'une par rapport à l'autre, leurs faces terminales respectives étant sensiblement parallèles, et leurs axes centraux respectifs sensiblement situés sur la même ligne.
PCT/US1995/009297 1994-07-29 1995-07-18 Attenuateur optique a surface partiellement reflechissante Ceased WO1996004580A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US28292894A 1994-07-29 1994-07-29
US08/282,928 1994-07-29

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WO1996004580A1 true WO1996004580A1 (fr) 1996-02-15

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2905642A1 (fr) * 2014-01-31 2015-08-12 OFS Fitel, LLC Terminaison de fibre optique avec faible rétroreflexion

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3044604A1 (de) * 1980-11-27 1982-06-24 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Optischer polarisator
JPS5885408A (ja) * 1981-11-16 1983-05-21 Matsushita Electric Works Ltd 光フアイバの結合装置
JPH0325403A (ja) * 1989-06-23 1991-02-04 Nec Corp 光減衰器
US5257335A (en) * 1991-01-23 1993-10-26 Nec Corporation Single mode optical fiber device including a short lens optical fiber

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3044604A1 (de) * 1980-11-27 1982-06-24 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Optischer polarisator
JPS5885408A (ja) * 1981-11-16 1983-05-21 Matsushita Electric Works Ltd 光フアイバの結合装置
JPH0325403A (ja) * 1989-06-23 1991-02-04 Nec Corp 光減衰器
US5257335A (en) * 1991-01-23 1993-10-26 Nec Corporation Single mode optical fiber device including a short lens optical fiber

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2905642A1 (fr) * 2014-01-31 2015-08-12 OFS Fitel, LLC Terminaison de fibre optique avec faible rétroreflexion
JP2015156019A (ja) * 2014-01-31 2015-08-27 オーエフエス ファイテル，エルエルシー 低後方反射の光ファイバ成端
JP2018163370A (ja) * 2014-01-31 2018-10-18 オーエフエス ファイテル，エルエルシー 低後方反射の光ファイバ成端

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