WO2003062887A1

WO2003062887A1 - Temperature compensated photonic package

Info

Publication number: WO2003062887A1
Application number: PCT/AU2003/000068
Authority: WO
Inventors: David John Robinson; David Allen Thorncraft; John Laurence Harris
Original assignee: Bishop Manufacturing Technology Limited
Priority date: 2002-01-25
Filing date: 2003-01-24
Publication date: 2003-07-31
Also published as: AUPS016402A0

Abstract

A temperature stable photonic device package (1) is disclosed, the package (1) including at least one length of optical fiber (3) which is loaded in tension over a portion of its length and supported by at least one pair of spaced-apart supports (2) carried by a carrier (4). Longitudinally aligned channels (6) are disposed in each pair of supports (2) for receiving a corresponding optical fiber. The optical fiber (3) is anchored within each of the channels (6) by means of solder (7). The supports (2) formed from a material that has a coefficient of thermal expansion that is lower than that of the carrier (4).

Description

TEMPERATURE COMPENSATED PHOTONIC PACKAGE

TECHNICAL FIELD

The present invention relates to a temperature compensated photonic package. Whilst the invention is primarily described with an embodiment particularly suited for a Bragg Grating that requires that the in-fiber grating is compensated for varying temperature such that the center wavelength remains constant, the present invention is also suitable for use with a variety of other photonic components or devices that require thermal compensation.

BACKGROUND

In-fiber Bragg gratings are well known and commonly comprise a repeated variation of refractive index written axially into a photosensitive optical fiber by UV or similar light source. The variation of refractive index and the resulting modulation pattern is inherently sensitive to effects of strain induced by mechanical or thermally variations in the optical fiber. For this reason, it is typical to mount the optical fiber containing the Bragg grating in a package so as to isolate the grating region from external strain or temperature effects. Typically, the mounted fiber containing the Bragg grating is mounted under tension within the package to affect a wavelength tuning function. For telecommunications applications, a one nanometer shift in Bragg wavelength over a 100°C temperature range in an uncompensated package can be a serious problem.

International Patent publication Nos. WO 98/59267 and WO 01/53862 both in the name of JDS Uniphase Pty Limited, disclose temperature compensated photonic device packages for Bragg gratings formed within an optical fiber. The packages described comprise fixing points on supports to which the optical fiber is anchored under tension by means of solder. The fixing points on the supports are housed within an elongate cylindrical carrier. The supports are manufactured from a material such as stainless steel or ceramic that has a greater coefficient of thermal expansion than that of the carrier that is made of a material such as Kovar or Invar. The combined expansion of the support and carrier materials produces a stable arrangement whereby the fixing points are maintained substantially at a fixed separation distance over a particular temperature range, thereby maintaining a substantially fixed strain on the optical fiber over that temperature range.

The elongate cylindrical carrier of the temperature compensated photonic device package disclosed in International Patent publication No. WO 98/59267 comprises a central thinned portion. By applying a controlled force to the thinned portion of the carrier a permanent plastic deformation may be applied to the package, thereby allowing the optical fiber to undergo strain and thereby so be tuned to a require center wavelength.

The temperature compensated photonic device package disclosed in International Patent publication No. WO 01/53862 has supports that are made of a material which has a coefficient of thermal expansion that is greater than that of the glass solder used to fix the optical fiber to the supports.

US6327405 (Leyva et al.) describes a temperature compensated package in which a base (carrier) made of Invar carrying cylindrical ferrules (supports) made of Kovar® for supporting the fibre. Compensating elements in the form of stainless steel rectangular pads are mounted above the base and support the cylindrical ferrules. The stainless steel compensating elements have a coefficient of expansion greater than that of both the Invar base and the Kovar supports. As the base, ferrules and compensating elements are each of differing materials, this arrangement involves complexity in its manufacture.

WO/42837 (Corning Incorporated) describes a passive temperature compensated package, wherein an optical fibre containing a fibre grating, is secured in tension within a hollow tube substrate body made from a material of negative coefficient of thermal expansion. This body is inturn contained within a hollow outer body with end caps, both of which may be made from materials such as stainless steel or Kovar®, glass, ceramic or other suitable material. The hollow outer body is fixed to the inner substrate body by centralised crimping, thereby allowing for symmetrical substrate shrinkage. This invention compensates for the change in performance in the fibre grating, due to varying temperature changes, by altering the tension in the fibre. For example if the temperature was to rise, the substrate would contract, thereby reducing the tension in the fibre, and theoretically, maintain the performance of the grating over a temperature range. Like previously mentioned prior art, this invention, is disadvantaged because of its cost and difficulty of manufacture. That is, multiple soldering, blind threading of fibre and crimping fixing methods such as those mentioned in this citation do not make this invention suitable for high volume, repetitive manufacture.

There are a number of disadvantages associated with the packages of the abovementioned prior art. Firstly, these packages utilize component parts that require complicated and costly manufacturing and assembly procedures. Secondly, the coefficient of thermal expansion of the solders used to fix the optical fiber to the supports are not ideally compatible with the support material, as a result of the supports being manufactured from a material such as stainless steel, whose coefficient of thermal expansion is greater than that of the carrier made of Kovar or the like.

SUMMARY OF THE INVENTION

According to a first aspect the present invention consists in a temperature stable photonic device package comprising at least one length of optical fiber which is loaded in tension over a portion of its length, at least one pair of spaced-apart supports for the at least one length of optical fiber, longitudinally aligned channels in the or each pair of supports for receiving a corresponding optical fiber, a carrier for carrying said supports, and solder anchoring the optical fiber within the channel of each of said supports characterised in that said supports being formed from a material that has a coefficient of thermal expansion that is lower than that of the carrier. Preferably said at least one pair of supports is attached to the carrier with each support having a respective attachment location to said carrier, and within said pair of supports the channel associated with one support is located a distance further away from its associated attachment location than that of the channel on the other support.

In one embodiment said channels in said supports are at or near opposite ends of the package and all channels are axially remote from said carrier.

In another embodiment said channels in said supports are at or near opposite ends of the package and all channels are axially inboard of said carrier. Preferably said package is surrounded by a housing that is movable relative to said carrier.

Preferably said supports are made from a material such as Kovar or Invar.

Preferably said carrier is made from a material such as stainless steel.

Preferably said carrier is substantially elongate. Preferably said carrier has a cylindrical configuration.

Preferably in one embodiment an in-fiber Bragg grating is formed within the tensile loaded portion of the at least one length of optical fiber. Preferably said package and the at least one length of optical fiber are adapted to undergo elongation to an extent sufficient to effect permanent plastic deformation of the package and to induce tensile strain in the Bragg grating and so tune the grating to a required centre wavelength.

In an alternative embodiment said package and the at least one length of optical fiber are adapted to undergo elongation by elastically deforming the package to induce tensile strain in the Bragg grating and so tune the grating to a required centre wavelength. In a first arrangement at least one cam wedge is inserted into a corresponding aperture on said carrier, and elastic deformation of said package is achieved by turning said cam wedge within said aperture. In a second arrangement said carrier has a threaded block and screw assembly mounted thereon, and elastic deformation of said package is achieved by turning said screw within said block. Preferably each of said channels has triangular or diamond shaped cavity therein in which said solder is seated.

Preferably said supports being formed from a material that has a coefficient of thermal expansion that is lower than that of the solder.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to drawings in which:

Figure 1 is a schematic perspective view of a first embodiment of a temperature stable photonic device package. Figure 2 is an enlarged perspective view of the support/channel and cavity detail of the package shown in Figure 1 with the solder omitted.

Figure 3 is a plan view of the support/channel and cavity detail of the package shown In Figure 2 with the fiber omitted.

Figure 4 is a perspective view of the support/channel and cavity detail of the package shown in Figure 2 with the solder.

Figure 5 is a plan view of an alternative embodiment of the support/channel and cavity detail.

Figure 6 is a perspective view of a first arrangement for the package of figure 1 to undergo elastic deformation utilising cam wedges. Figure 7 is a schematic showing the profile of a cam wedge as shown in Figure

6 relative to its aperture.

Figure 8 is a perspective view of a first arrangement for the package of Figure 1 to undergo elastic deformation utilising a threaded block and screw assembly.

Figure 9 is a schematic perspective view of a second embodiment of a temperature stable photonic device package.

Figure 10 is a schematic perspective view of a third embodiment of a temperature stable photonic device package.

Figure 11 is a schematic underside perspective view of the package shown in Figure 10. Figure 12 is a schematic perspective view of a fourth embodiment of a temperature stable photonic device package.

MODE OF CARRYING OUT INVENTION Figure 1 depicts a first preferred embodiment of a temperature stable photonic device package 1 of the present invention. Package 1 comprises two supports 2 for supporting a length of optical fiber 3. Supports 2 are mounted on an elongate carrier 4.

A Bragg grating is formed within a portion of fiber 3 that is indicated schematically in Figure 1 by the exaggerated fiber thickness 5. The grating- containing portion of optical fiber 3 that extends between supports 2 is loaded in tension to an extent required to impose a requisite degree of strain therein. The level of strain that is imposed will be dependent upon that required to tune the grating to a selected centre wavelength.

Carrier 4 is formed from a material such as stainless steel. Supports 2 are formed from a material that has a coefficient of thermal expansion that is lower than that of carrier 4, such as Kovar or Invar.

Fiber 3 is anchored in longitudinally aligned channels 6 in the respective supports 2 by means of solder 7, such as a conventional glass solder or epoxy adhesive. Preferably the Invar or Kovar supports 2 have a coefficient of thermal expansion that is lower than that of solder 7. One suitable solder material that has a coefficient of thermal expansion greater than the Invar or Kovar supports 2, is a glass fritt provided on a plastic layer as a glass transfer tape, and is marketed by Vitta Corporation in the United States of America under the code "G-1014". This glass fritt is generally suitable for glazing and sealing Beryllia and Allumina-Kovar packages.

Longitudinally aligned channels 6 in respective supports 2 are near opposite ends of the package 1 and are both axially remote from carrier 4, ie they are located axially outboard relative to said carrier. In order to position the channels

6 at near opposite ends of package 1 remote from carrier 4, each support 2 is attached to carrier 4 at a respective attachment location 15. Each channel 6 associated with a support 2 is located a distance further away from its associated attachment location 15 than that of the other channel 6 on the other support 2. In this embodiment the attachment locations 15 are at opposite ends of carrier 4.

Each channel 6 is located in raised portion 2a of its respective support 2. Whilst channels 6 may be conventional elongate grooves, it is preferable that a triangular or diamond shaped cavity 8 is located within each channel 6 where solder 7 is seated as shown in Figures 2, 3 and 4. The triangular or diamond shaped cavity 8 ensures that the solder 7, is mechanically locked into position, thereby providing increased shear strength between solder 7 and support 2. In an alternative embodiment a plurality of triangular or diamond shaped cavities 8a within the channel 6 where solder 7 is seated, as shown in Figure 5.

In a similar manner to that described in the prior art International Patent publication No. WO 98/59267, package 1 and the optical fiber 3 may undergo an elongation to an extent sufficient to effect permanent plastic deformation of package 1 and to induce tensile strain in the Bragg grating and so tune the grating to a required centre wavelength. This may be achieved by providing carrier 4 or supports 2 with a thinned section (not shown) upon which a controlled force may be applied.

Alternatively, package 1 and optical fiber 3 are adapted to undergo elongation by elastically deforming the package to induce tensile strain in the Bragg grating and so tune the grating to a required centre wavelength.

A first arrangement that allows for package 1 to undergo elastic deformation is shown in Figures 6 and 7. This arrangement utilises elliptically shaped cam wedges 9 that are inserted into corresponding elliptically shaped apertures 10 on carrier 4. An enlarged profile of a cam wedge 9 relative to its corresponding aperture 10 is shown in Figure 7. Elastic deformation of package 1 is achieved by turning cam wedge 9 within aperture 10. A second arrangement that allows for package 1 to undergo elastic deformation is shown in Figure 8. This arrangement utilises a threaded block and screw assembly 11 mounted on carrier 4, and elastic deformation of package 1 is achieved by turning screw 12 within blocks 13. An aperture 16 is located on carrier 4 to more readily allow carrier 4 to undergo elongation during elastic deformation of package 1. Figure 9 depicts a second preferred embodiment of a temperature stable photonic device package 101 of the present invention. In a similar manner to the first embodiment, package 101 has an elongate carrier 104 formed from a material such as stainless steel. However in this embodiment, the carrier 104 carries four pairs of supports 102, each pair of supports supporting an optical fiber 103. The supports 102, like supports 2 of the first embodiment are formed from a material that has a coefficient of thermal expansion that is lower than that of carrier 104, such as Kovar or Invar. Also, the solder and channels used in this embodiment are similar to those described in the first embodiment. This embodiment may utilise means for tuning the grating to a required centre wavelength either by plastic or elastic deformation in a like manner to the first embodiment.

Figures 10 and 11 depict a third preferred embodiment of a temperature stable photonic device package 201 of the present invention. In a similar manner to the first embodiment, package 201 has an elongate carrier 204 formed from a material such as stainless steel and a pair of supports 202 supporting an optical fiber 203. The supports 202, like supports 2 of the first embodiment are formed from a material that has a coefficient of thermal expansion that is lower than that of carrier 204, such as Kovar or Invar. Also, the solder and channels used in this embodiment are similar to those described in the first embodiment. Whilst each channel 206 associated with a support 202, is located a distance further away from its associated attachment point 215 than that of the other channel 206 on the other support 202, the attachment points 215 are located on the underside of carrier 204 away from the ends of the carrier 204.

Figure 12 depicts a fourth preferred embodiment of a temperature stable photonic device package 301 of the present invention. In a similar manner to the first embodiment, package 301 has an elongate carrier 304 formed from a material such as stainless steel and a pair of supports 302 supporting an optical fiber 303. The supports 302, like supports 2 of the first embodiment are formed from a material that has a coefficient of thermal expansion that is lower than that of carrier 304, such as Kovar or Invar. Also, the solder and channels used in this embodiment are similar to those described in the first embodiment. Longitudinally aligned channels 306 in respective supports 302 are near opposite ends of the package 1 and are both located axially inboard relative to said carrier 304. Whilst each channel 306 associated with a support 302, is located a distance further away from its associated attachment point 315 than that of the other channel 306 on the other support 302, the attachment points 315 are located on the upperside 318 of carrier 304 away from the ends of the carrier 304.

In all four embodiments described above, package 1 , 101, 201 301 , is preferably surrounded by a housing (not shown) that is attached to carrier 4,104 204 or 304. The housing is preferably semi-rigidly attached to carrier 4,104, 204 or 304, to allow for relative movement therebetween. The housing may preferably be of an inexpensive material, such as plastic.

In all four embodiments, the main portions of supports 2, 102, 202 or 302, are made of relatively thin sheets of Invar and Kovar, which are directly fastened to their respective carriers 4, 104, 204 or 304, by rivets or other suitable fasteners. No intermediate compensating elements or materials are required between supports 2, 102, 202 or 302 and their respective carriers 4,104, 204 or 304.

The packages 1 , 101 , 201 and 301 are generally less expensive in materials and manufacture than that of the earlier described prior art packages that utilise Invar or Kovar carriers and stainless steel supports located therein. The use of supports made of Invar or Kovar whose coefficient of thermal expansion is lower than that of a carrier made of stainless steel , results in an improved compatibility between the solder the support to which it is attached.

It should also be understood that whilst the second embodiment depicts carrier 104 holding four pairs of supports 102, in other not shown embodiments, a cylindrical carrier may carry two, three or five or more pairs of supports such that a plurality of fibres may be supported by the carrier. The term "solder" as used herein is used to describe any suitable material for adhering the fiber to the channels located on the supports, and may include material such as a conventional glass solder or an epoxy adhesive.

The term "comprising" as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of.

Claims

CLAIMS:

1. A temperature stable photonic device package comprising at least one length of optical fiber which is loaded in tension over a portion of its length, at least one pair of spaced-apart supports for the at least one length of optical fiber, longitudinally aligned channels in the or each pair of supports for receiving a corresponding optical fiber, a carrier for carrying said supports, and solder anchoring the optical fiber within the channel of each of said supports characterised in that said supports being formed from a material that has a coefficient of thermal expansion that is lower than that of the carrier.

2. A temperature stable photonic device package as claimed in claim 1 , wherein said at least one pair of supports is attached to the carrier with each support having a respective attachment location to said carrier, and within said pair of supports the channel associated with one support is located a distance further away from its associated attachment location than that of the channel on the other support.

3. A temperature stable photonic device package as claimed in claim 1 , wherein said channels in said supports are at or near opposite ends of the package and all channels are axially remote from said carrier.

4. A temperature stable photonic device package as claimed in claim 1 , wherein said channels in said supports are at or near opposite ends of the package and all channels are axially inboard of said carrier.

5. A temperature stable photonic device package as claimed in claims 1 -4, wherein said package is surrounded by a housing that is movable relative to said carrier.

6. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein said supports are made from a material such as Kovar or Invar.

7. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein said carrier is made from a material such as stainless steel.

8. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein said carrier is substantially elongate.

9. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein said carrier has a cylindrical configuration.

10. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein an in-fiber Bragg grating is formed within the tensile loaded portion of the at least one length of optical fiber.

11. A temperature stable photonic device package as claimed in claim 10, wherein said package and the at least one length of optical fiber are adapted to undergo elongation to an extent sufficient to effect permanent plastic deformation of the package and to induce tensile strain in the Bragg grating and so tune the grating to a required centre wavelength.

12. A temperature stable photonic device package as claimed in claim 10, wherein said package and the at least one length of optical fiber are adapted to undergo elongation by elastically deforming the package to induce tensile strain in the Bragg grating and so tune the grating to a required centre wavelength.

13. A temperature stable photonic device package as claimed in claim 12, wherein at least one cam wedge is inserted into a corresponding aperture on said carrier, and elastic deformation of said package is achieved by turning said cam wedge within said aperture. 14. A temperature stable photonic device package as claimed in claim 12, wherein said carrier has a threaded block and screw assembly mounted thereon, and elastic deformation of said package is achieved by turning said screw within said block.

15. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein each of said channels has triangular or diamond shaped cavity therein in which said solder is seated.

6. A temperature stable photonic device package as claimed in any one of the preceding claims, wherein said supports being formed from a material that has a coefficient of thermal expansion that is lower than that of the solder.