GB2385678A

GB2385678A - Mthod of joining optical components using adhesive

Info

Publication number: GB2385678A
Application number: GB0214642A
Authority: GB
Inventors: Stephen Tyler; Paul Westmarland
Original assignee: Bookham Technology PLC
Current assignee: Lumentum Technology UK Ltd
Priority date: 2002-02-20
Filing date: 2002-06-25
Publication date: 2003-08-27
Also published as: GB0214642D0

Abstract

A method of joining an optical component 42 to an optic chip 48 to form an optical connection at an optical interface that terminates at an edge 46 of the optic chip 48. The method including the use of a first adhesive 50 at one or more selected locations other than the optical interface to secure the optical component 42 and the optic chip 48 together whilst leaving the optical interface clear of said first adhesive 50. The adhesive 50 may be used to encapsulate an optical material, such as refractive index matching gel 44, at the optical interface. The adhesive 50 may be solder or epoxy adhesive and have a second line 52. The optical interface may also be an air gap where the edges 46, 40 of the optical chip 48 and the optical component 42, which may be a waveguide, are polished. Also disclosed is a shell structure connected to an optic chip by adhesive. Also disclosed is a method of joining an optic fibre block to an optic chip by mounting the optic fibre block on a planar support at an angle to the plane.

Description

METHOD OF JOINING OPTICAL COMPONENTS The present invention relates to a method of joining optical components, and particularly to a method of joining an optical component to the edge of an optic chip to achieve an optical connection between an optical component and an optic element of the optic chip that terminates at the edge of the optic chip.

Optic chips typically include one or more optic elements for generating one or more optic signals for transmission to one or more external locations along one or more optic fibres, or for processing one or more optic signals received from one or more external sources via one or more optic fibres. A common technique for connecting the optic fibres to the chip is as follows. The optic chip defines one or more waveguides extending to a polished edge of the chip and the ends of one or more optic fibres are aligned with the ends of the one or more waveguides at the polished chip edge. The optic fibres are normally held in the aligned condition using a fibre block having a polished leading face coplanar with the ends of the optic fibres. The fibre block is secured to the optic chip by application of an epoxy adhesive between the polished edge of the chip and the polished face of the fibre block at which the optic fibre ends are located. Each optic fibre is aligned with the respective waveguides with its axis at an angle to that of the respective waveguide to reduce undesirable back reflection effects. To this end, the edge of the chip is normally polished at an angle other than 90 degrees with respect to the plane of the chip. This conventional technique is illustrated in Figure 1, in which the epoxy adhesive, which also occupies the optical interface, is shown by hatching.

It is an aim of the present invention to provide an alternative technique for joining an optical component to the edge of an optic chip.

According to a first aspect of the present invention, there is provided a method of joining an optical component to an optic chip to form an optical connection at an optical interface between the optical component and an optic element of

the optic chip that terminates at an edge of the optic chip, the method including the use of a first adhesive at one or more selected locations other than the optical interface to secure the optical component and the optic chip together whilst leaving the optical interface clear of said first adhesive, whereby the first adhesive can be optimised for its mechanical properties without regard to its optical properties.

According to another aspect of the present invention, there is provided an optic assembly including an optical component joined to an optic chip to achieve an optical connection at an optical interface between an optic element of the optic chip that terminates at an edge of the optical chip and the optical component, wherein the optical component and the optic chip are secured together by the use of a first adhesive at one or more selected locations other than the optical interface.

According to another aspect of the present invention, there is provided a method of joining a fibre block to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held by the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, the method including the steps of : arranging the fibre block at the edge of the chip such that the end of the at least one optic fibre is aligned with the end of the at least one respective waveguide; providing a separate optical material at the interface for optimising the optical connection; and securing the optic chip and the fibre block together by the use of adhesive, the adhesive being applied so as to encapsulate the optical material.

According to another aspect of the present invention, there is provided an optic assembly including a fibre block joined to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held by the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, wherein a separate optical material is provided at the interface for optimising the optical connection; and

the optic chip and the fibre block are secured together by the use of adhesive, the adhesive being applied so as to encapsulate the optical material.

According to another aspect of the present invention, there is provided a method of joining a fibre block to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held at one end of the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, the method including the steps of : providing a shell structure including openings for respectively receiving said end of the fibre block and a portion of the polished edge of the optic chip at which the waveguides terminate; inserting said end of the fibre block and said portion of the polished edge of the optic chip into the shell structure via the openings so as to align the end of the least one optic fibre with the end of the at least one respective waveguide; securing by adhesive the fibre block and optic chip to the shell structure; and supplying an optical material into the shell structure via a supply hole defined in a wall of the shell structure so as to fill the optical interface with the optical material.

According to another aspect of the present invention, there is provided an optic assembly including a fibre block joined to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held at one end of the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, wherein said end of the fibre block and a portion of the polished edge of the optic chip at which the waveguides terminate are secured in an aligned configuration within a shell structure, the shell structure defining together with the fibre block and optic chip a receptacle in which an optical material is provided to fill the optical interface.

According to another aspect of the present invention, there is provided a method of joining a planar fibre block, which holds at least one optic fibre parallel to the plane of the block, to a polished edge of an optical chip to form

an optical connection at an optical interface between an end of the at least one optic fibre held at one end of the optic fibre block and the end of at least one respective planar waveguide extending to the polished edge of the optic chip, the method including the steps of : securing the optic chip to a planar support; mounting the fibre block on the planar support at an angle to the plane thereof such that the end of the at least one optic fibre is optically aligned with the end of the waveguide but at an angle to the plane thereof to reduce undesirable back reflection effects; and securing by adhesive the fibre block to the planar support so as to leave an air gap at the optical interface between the end of the least one optic fibre and the end of the at least one respective waveguide.

According to another aspect of the present invention, there is provided an optic assembly including a planar fibre block, which holds at least one optic fibre parallel to the plane of the block, joined to an optic chip to form an optical connection at an optical interface between an end of the at least one optic fibre held at one end of the optic fibre block and the end of at least one respective planar waveguide extending to a polished edge of the optic chip, wherein the optic chip is secured to a planar support; the fibre block is also secured to the planar support by adhesive such that the end of the at least one optic fibre is optically aligned with the end of the at least one waveguide but at an angle to the plane thereof to reduce undesirable back reflection effects; and an air gap is provided at the optical interface between the end of the least one optic fibre and the end of the at least one respective waveguide.

Embodiments of the present invention are described hereunder, by way of nonlimiting example only, with reference to the accompanying drawings, in which :- Figure 1 illustrates a conventional technique for joining a fibre block to the edge of an optic chip; Figures 2 to 4 illustrate a method according to a first embodiment of the present invention;

Figure 5 illustrates a variation of the type of method illustrated in Figures 2 to 4 ; Figure 6 illustrates a method according to a second embodiment of the present invention; Figure 7 illustrates a method according to a third embodiment of the present invention; Figures 8 and 9 illustrate, in cross-section, the edge of the chip and the leading face of the optic fibre block to be joined in the embodiments of the present invention shown in Figures 2 to 7.

The embodiments of the method of the present invention described hereunder are each directed to the joining of a fibre block supporting an array of silica optic fibres with an edge of a silicon-on-insulator (SOI) optic chip at which a respective array of rib waveguides terminate. With reference to Figure 8, the optic chip includes a layer of epitaxial silicon 2 supported on a silicon substrate 4 via a silicon oxide confinement layer 6. In the epitaxial layer 2 are defined an array of rib waveguides 8, which in use may transmit the input/output of a AWG-based multiplexer/demultiplexer (not shown) also defined in the epitaxial layer 2 and which terminate at the edge of the optic chip, as shown in Figure 8 (i. e. the ends of the waveguides are coplanar with the edge of the optic chip). With reference to Figure 9, the array of silicon fibres 10 are supported in a configuration corresponding to that of the array of waveguides 8 by a silicon fibre block 12 comprising two silicon half-blocks 14,16 each provided with complementary V-grooves 18 at their joining surfaces for holding the array of fibres in the desired configuration. As shown in Figure 9, the optic fibres terminate at the leading face of the fibre block (i. e. they are coplanar with the leading face of the fibre block). The edge of the optic chip at which the array of waveguides terminate and the leading face of the fibre block are polished, which may be done according to a standard technique.

With reference to Figures 2 to 4, there is described a method according to a first embodiment of the present invention of joining the fibre block 17 to the

polished edge 19 of an SOI optic chip 18 to create an optical connection between the array of waveguides and the array of optic fibres.

There is provided a hollow shell structure 20 consisting of a single piece of kovar or ceramic. These materials are preferable because they have a similar co-efficient of thermal expansion (CTE) to that of the optic chip material, which helps to maintain optical alignments under differing temperatures.

The shell structure includes an opening at one side and a pair of slots 22 machined in the side walls to receive an edge portion of the optic chip including the part of the polished edge at which the array of waveguides terminate. The shell structure 20 is slotted onto the optic chip in such a way that all the ends of the array of waveguides are located within the shell with the polished edge of the chip butting up to the back edges 24 of the slots 22. The shell structure 20 is then secured to the optic chip using epoxy adhesive 28 around the chip slot edges. Care should be taken to ensure that the waveguides are located centrally within the shell, and that the polished edge including the ends of the waveguides is not damaged when fitting the shell. Fiducial marks on the optic chip, or a setting jig can be used to help this operation.

The shell structure includes a further opening 30 at an opposite side for receiving the optic fibre block. The optic fibre block is introduced into the opening 30 of the shell structure using a mechanical or vacuum fibre block gripper (not shown). A section of the lower wall of the shell structure is cut back 30 compared to the side walls and upper wall to allow access for the fibre block gripper as the leading face of the fibre block is moved into position within the shell structure. This allows a greater area of fibre block to be securely gripped by the fibre block gripper right up to the final positioning of the leading face of the fibre block within the shell structure.

Initial alignment of the fibre block can be achieved visually via visual alignment slots 26. A parallel alignment of the polished leading face of the

fibre block with the polished edge chip can be established prior to this operation by checking alignment to the visible portion of the chip edge protruding from the shell structure. Once the leading face of the fibre block is in the final position with the ends of the optic fibres having been actively aligned with the ends of the array of waveguides, the fibre block is secured to the shell structure using epoxy adhesive 32 dispensed onto the fibre block around its girth. An epoxy curable either by UV or thermally can be used. The epoxy adhesive is preferably of a high viscosity to help prevention of the adhesive running into the shell structure and entering the space between the leading face of the fibre block and the polished edge of the optic chip.

The space between the edge of the optic chip and the leading face of the fibre block, which defines the optical interfaces between the ends of the waveguides and the ends of the optic fibres, now lies in a receptacle partially defined by the lower and side walls of the shell structure. Access to this space from above exists via a gel dispense hole 34 defined in the upper wall of the shell structure.

This hole is tapered to easily accept a hollow needle and is located centrally over the space between the optic chip edge and the leading face of the fibre block. This space is filled with refractive-index matching gel via the gel dispense hole using a hollow needle to optimise the optical coupling between the waveguides and the optic fibres.

As already indicated above, visual alignment slots 26 are provided in an upper wall of the shell structure to allow a first light alignment of the fibre block to the waveguides. They also allow visual confirmation that the refractive-index matching gel injected through the gel dispense hole has reached both side extremities of the leading face of the fibre block. This could alternatively be confirmed by observing a decrease in optical power loss on the outer aligned channels.

As shown in Figure 5, in a variation of the above-described method, the order of the steps could be reversed with the shell structure being first attached to the

fibre block, and the fibre block/shell structure assembly then being slotted onto the optic chip. In this case, the shell structure should be relatively accurately machined to facilitate location of the leading face of the fibre block in the correct position for alignment with the waveguides when the shell structure is subsequently slotted onto the optic chip; or, the slots for receiving the optic chip should be formed with relatively large clearances to allow the fibre block/shell structure assembly to be manoeuvred relative to the optic chip into the correct position to achieve the desired alignment.

With reference to Figure 6, a method according to a second embodiment of the present invention is now described.

In this method, the polished edge 46 of the optic chip 48 at which the waveguides terminate, as shown in Figure 8, is coated with an excess of refractive-index matching gel 44, such as a silicone gel, and is then pressed against the polished leading face 40 of the fibre block 42 shown in Figure 9. A controlled volume of silicone gel is used to ensure that the gap between the edge of the optic chip and the leading face of the fibre block is completely filled with the silicon gel by surface tension.

The fibre block 40 is then manoeuvred relative to the optic chip 48 in an active alignment process to align the ends of the fibres with the ends of the waveguides. Once the alignment has been optimised, the silicone gel is heat cured, and then overcoated with epoxy adhesive to encapsulate it by supplying a line of adhesive around the joint between the fibre block and the optic chip. According to one technique, a first line of epoxy adhesive 50 is supplied via a hypodermic needle to the top of the joint between the fibre block and the optic chip; the optic chip/fibre block assembly of edge of the optic chip is then flipped and a second line 52 of epoxy adhesive is supplied to the opposite side of the joint between the optic chip and the fibre block. The two lines of epoxy adhesive each flow down the side of the joints between the fibre block and optic chip and meet to encapsulate the

refractive-index matching gel. The epoxy adhesive is cured either thermally or by UV radiation to secure the optic chip to the fibre block and mechanically support the fibre block on the optic chip in the aligned configuration. The epoxy adhesive is characterised by relatively low shrinkage and high stiffness/rigidity.

In this embodiment, the optic fibres are aligned with the waveguides but at an angle to the plane of thereof, which serves to reduce undesirable backreflection effects. To this end, the edge of the optic chip at which the waveguides terminate is polished at an angle (i. e. other than perpendicularly) to the plane of the optic chip (and hence the plane of the waveguides), and the leading face of the fibre block is polished perpendicularly to the plane of the array of the optic fibres.

With reference to Figure 7, a method for joining an array of optics fibres to an edge of an optic chip according to a third embodiment of the present invention is now described.

As with the previous embodiment, a planar fibre block 70 holds an array of fibres in the plane of the block with the ends of the fibres coplanar with a polished leading face of the fibre block, as illustrated in Figure 9. As in the previous embodiment, the aim is to support the leading face of the fibre block against the polished edge of the chip with the optic fibres aligned with the ends of the waveguides, but at an angle to the plane of the chip.

The optic chip 72 having a polished edge with an array of waveguides terminating at the edge, as shown in Figure 8, is securely mounted on a planar ceramic support 74. A ceramic wedge (shoe) 76 is also securely mounted on the planar support 74 at a spaced location from the optic chip for supporting the fibre block 70 at the desired angle to the plane of the support 74, and hence at the desired angle to the plane of the optic chip. The edge of the optic chip

and/or the leading face of the optic fibre block are accordingly polished at a corresponding angle. The fibre block is mounted on the ceramic wedge 76 via a layer of epoxy adhesive 78 with a 5 micron air gap interface 80 between the leading face of the fibre block and the polished edge of the optic chip at which the waveguides terminate. Once the optic fibres have been actively aligned with the waveguides, the epoxy adhesive is cured thermally or by using UV radiation.

In each of the techniques described in detail above, a secure mechanical connection is achieved using an epoxy adhesive whilst avoiding the use of epoxy adhesive at the optical interface in favour of the use of a different optical material.

The applicant draws attention to the fact that the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof, without limitation to the scope of any definitions set out above. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS: 1. A method of joining an optical component to an optic chip to form an optical connection at an optical interface between the optical component and an optic element of the optic chip that terminates at an edge of the optic chip, the method including the use of a first adhesive at one or more selected locations other than the optical interface to secure the optical component and the optic chip together whilst leaving the optical interface clear of said first adhesive, whereby the first adhesive can be optimised for its mechanical properties without regard to its optical properties.
2. A method according to claim 1, including the step of providing a separate optical material at the optical interface to optimise the optical connection.
3. A method according to claim 2, wherein the adhesive is used so as to encapsulate the optical material at the optical interface.
4. A method according to claim 1, wherein the optical interface includes an air gap.
5. A method according to any preceding claim wherein the adhesive is a solder or an epoxy adhesive.
6. A method according to any preceding claim wherein the edge of the chip including the end of the optic element is polished.
7. A method according to any preceding claim wherein the optic element is an optic waveguide that extends to the edge of the optic chip.
8. An optic assembly including an optical component joined to an optic chip to achieve an optical connection at an optical interface between an optic

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element of the optic chip that terminates at an edge of the optical chip and the optical component, wherein the optical component and the optic chip are secured together by the use of a first adhesive at one or more selected locations other than the optical interface.
9. A method of joining a fibre block to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held by the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, the method including the steps of : arranging the fibre block at the edge of the chip such that the end of the at least one optic fibre is aligned with the end of the at least one respective waveguide; providing a separate optical material at the interface for optimising the optical connection; and securing the optic chip and the fibre block together by the use of adhesive, the adhesive being applied so as to encapsulate the optical material.
10. An optic assembly including a fibre block joined to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held by the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, wherein a separate optical material is provided at the interface for optimising the optical connection; and the optic chip and the fibre block are secured together by the use of adhesive, the adhesive being applied so as to encapsulate the optical material.
11. A method of joining a fibre block to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held at one end of the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, the method including the steps of : providing a shell structure including openings for respectively receiving said end of the fibre block and a portion of the polished edge of the optic chip at which the waveguides terminate ; inserting said end of the fibre

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block and said portion of the polished edge of the optic chip into the shell structure via the openings so as to align the end of the least one optic fibre with the end of the at least one respective waveguide; securing by adhesive the fibre block and optic chip to the shell structure; and supplying an optical material into the shell structure via a supply hole defined in a wall of the shell structure so as to fill the optical interface with the optical material.
12. An optic assembly including a fibre block joined to an optic chip to form an optical connection at an optical interface between the end of at least one optic fibre held at one end of the optic fibre block and the end of at least one respective waveguide extending to a polished edge of the optic chip, wherein said end of the fibre block and a portion of the polished edge of the optic chip at which the waveguides terminate are secured in an aligned configuration within a shell structure, the shell structure defining together with the fibre block and optic chip a receptacle in which an optical material is provided to fill the optical interface.
13. A method of joining a planar fibre block, which holds at least one optic fibre parallel to the plane of the block, to a polished edge of an optical chip to form an optical connection at an optical interface between an end of the at least one optic fibre held at one end of the optic fibre block and the end of at least one respective planar waveguide extending to the polished edge of the optic chip, the method including the steps of : securing the optic chip to a planar support ; mounting the fibre block on the planar support at an angle to the plane thereof such that the end of the at least one optic fibre is optically aligned with the end of the waveguide but at an angle to the plane thereof to reduce undesirable back reflection effects; and securing by adhesive the fibre block to the planar support so as to leave an air gap at the optical interface between the end of the least one optic fibre and the end of the at least one respective waveguide.

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14. An optic assembly including a planar fibre block, which holds at least one optic fibre parallel to the plane of the block, joined to an optic chip to form an optical connection at an optical interface between an end of the at least one optic fibre held at one end of the optic fibre block and the end of at least one respective planar waveguide extending to a polished edge of the optic chip, wherein the optic chip is secured to a planar support; the fibre block is also secured to the planar support by adhesive such that the end of the at least one optic fibre is optically aligned with the end of the at least one waveguide but at an angle to the plane thereof to reduce undesirable back reflection effects; and an air gap is provided at the optical interface between the end of the least one optic fibre and the end of the at least one respective waveguide.
15. A method for joining an optical component to optic chip substantially as hereinbefore described with reference to Figures 2 to 7 of the accompanying drawings.
16. An optic assembly substantially as hereinbefore described with reference to Figures 4,6 and 7 of the accompanying drawings.