AU660356B2 - Optical connector - Google Patents

Description

b356 P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

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COMPLETE SPECIFICATI(:) STANDARD PATENT Invention Title: "OPTICAL CONNECTOR" The following statement is a full description of this invention, including the best -ntdhod of performing it known to us:- This invention relates to buried channel planar waveguides fabricated on a planar substrate for fibre-optic applications, and in particular to a method and device for aligning fibre-optic pigtails with the waveguide ends for minimum fibre-to-waveguide connection loss when the fibre pigtails are subsequently attached.

In fibre-optic applications one of the most common components is the fibre-optic coupler for separating and/or combining signals. These couplers can be in the form of a so-called tree coupler which is used to split a single optical channel into multiple output channels or combine signals from multiple channels into one; a star coupler which typically has an equal number of input and output ports, eg. 4 x 4; and wavelength division multiplexer/demultiplexers for separating input signals of different wavelengths onto one fibre.

Prior art couplers have been based on three fabrication technologies: 1. Micro-optics which utilise micro devices such as beam splitters and micro-lenses.

2. Fibre fusion or fused biconic taper which relies on the melting and drawing of fibres to bring their cores into close proximity to allow coupling.

3. Fibre lapping in which the fibres to be coupled are ground down to their core region and placed together to achieve coupling.

The latest known technology in which couplers are based is integratic-i .technology in which buried channel planar waveguides are formed on a glass substrate .by, for example, a process of an ion exchange into exposed areas of a glass substrate; flame hydrolysis deposition and reactive ion etching; or diffusion plasma processing.

V-shaped grooves are formed in the surface at the edge of the substrate to expose ends *o of the formed waveguides and then optical fibre pigtail are axially aligned with ends of the waveguides and adhered thereto.

Tolerances on standard single mode fibre used for the pigtails allow 2-3 microns of eccentricity in the fibre core which is fairly consistent over short sections of fibre.

This eccentricity is too inaccurate to enable precise alignment of the pigtails without some form of manipulation, and it is therefore necessary to align each fibre pigtail separately using a micro-manipulator device which is time consuming r ii 0ifficulc as adjacent waveguide ends may only be 1 mm or so apart.

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It is an object of the present invention to provide a method and apparatus for simply and accurately aligning the cores of a plurality of standard fibre pigtails with the ends of buried channel planar waveguides. The method and apparatus of the present invention obviates the need for alignmenti0 grooves in the substrate.

According to the invention there is provided a method of aligning a plurality of optical fibre pigtails with respective ends of a plurality of buried channel planar waveguidesburied in a layer on a substrate of a waveguide chip, the centres of at least two adjoining planar waveguide ends being spaced from each other by a first distance, and the centres of said waveguide ends being at a height from a first surface extending in a plane parallel to said planar waveguides from said substrate by a second distance, said method comprising the steps of: a. Support on support means each said optical fibre pigtail in a parallel spaced relationship so that said centres cf the optical fibre pigtail ends are spaced by said first distance and at a height from a reference surface on said support means corresponding to said second distance; b. Launch light into the supported optical fibre pigtails to illuminate, during the subsequent step, said optical fibre pigtail cores; c. Rotate each supported optical fibre pigtail into a position where its illuminated core centre is spaced from said reference surface by said second distance, all so positioned cores being on the same side of their associated waveguide end centre; d. Fix said optical fibre pigtails in said position in the support means; Se. Interface said ends of the fixed optical fibre pigtails with the said waveguide ends; f. Launch light into one optical fibre pigtail and sense light energy at the opposite end uf at least one other optical iibre pigtail; g. Align core centres of said optical fibre pigtail ends with said waveguide ends by adjusting lateral location of said support means for maximum level of sensed light energy.

h. Fix the aligned fibre pigtails in the so aligned position.

According to a further aspect of the present invention there is provided a device for aligning a plurality of optical fibre pigtails with respective ends of a plurality of buried channel planar waveguides in a substrate, the centres of at least two adjoining planar waveguide ends being spaced from each other by a first distance, and the centres of said waveguide ends being at a height from a first surface extending in a plane parallel to said planar waveguides from said substrate by a second distance, said device comprising a support means arranged to support each said optical fibre pigtail in a parallel spyaced relationship so that said centres of the optical fibre pigtails ends are spaced by said first distance and at a height from a reference surface on said support means corresponding to said secondi6 distance, means to launch light into the supported optical fibre pigtail cores, comparator means arranged to compare the position of illuminated core centre of each utical fibre pigtail with a reference means corresponding to said second distance, said illuminated core centre being brought to said second distance by rotation of said fibre optic pigtail and then laterally aligned with said waveguide centres.

In order that the invention may be readily carried into effect embodiments i:4* thereof will now be described in re'4tion to the accompanying drawings, in which: Figure 1 shows a cross sectional view of a support block supporting fibre pigtails to be aligned with waveguides buried in a waveguide chip also shown, according to the present invention.

Figure 2 is a perspective representation of the device for adjusting and setting the height of the fibre pigtail cores, according to the invention.

Figure 3 is a perspective representation of the support block supporting height adjusted fibre pigtails and the waveguide chip on a base for horizontal alignment 20 according to the invention.

Figure 4 is a perspective representation of an alternative horizontal alignment arrangement.

Referring to Figure 1, a rectangular support block 1 of glass is provided with three parallel V-shaped grooves 2, 3 and 4, dimensioned such that the distance (y) between the centre of each fibre pigtail 5, 6 and 7 supported within respective grooves is equal to the distance between a horizontal plane bisecting buried rectangular waveguides 8, 9 and 10 in a waveguide chip 11 and the bottom surface of chip 11; which comprises, in addition to the waveguides 8, 9 and 10, a silicon substrate S, a first silica layer S1, a second silica core layer S2, and a cladding layer S3, the waveguides being etched into the said core layer. The spatial relationship of grooves 2, 3 and 4 is such that the vertex of each groove and an opposite waveguide are bisected Ly a vertical plane (shown in broken lines). Thus the centre of each supported fibre pigtail 5, 6 and 7 coincides with the centres of respective waveguides 8, 9 and 10, It will be understood that the cross sectional shape of buried waveguides 8, 9 and may be square.

the support block 1 shown has one group of three parallel grooves; however, to allow for tolerance of optical fibre, the block may be provided with several groups of parallel grooves, each group being of a different depth. The different groups may be accommodated on support block 1 in the form of a grid, one group of parallel grooves being at right angle to the other group. Another such grid may be provided on the opposite surface of support block 1, thereby providing four groups of grooves of different depths.

Referring to Figure 2, support block 1 is supported on a base 12, and the fibre pigtails 5, 6 and 7 are restrained by a pad 13 of resilient material such as, for example, rubber. Base 12 also supports a known magnifying lens and optical grating arrangement 14 operatively located opposite the fibre pigtail ends. Light from a light source 15 is launched into the fibre pigtails and a TV camera 16 picks up an image of that light emerging from cores 17, 18 and 19 via magnifying lens and optical grating 14 and converts thei6 image into electrical signals which are processed in a video data processor (not shown) and images 20, 21 and 22 of the core projected through the grating are displayed in a monitor screen 23. Each fibre pigtail is rotated until the image of the core centre on screen 23 indicates that the core centre is at height y (Figure 1) and at the same side of the horizontal plane bisecting the vertex of the supporting groove. When the core centres are so positioned they are affixed to support block 1 by an adhesive, for example U.V. cured epoxy, and pad 13 is then removed.

S° Referring to Figure 3, support block 1 complete with affixed pigtails is placed on a ledge 24 that has been previously cut into waveguide chip 11 at a depth y, and using light injection (not shown) into core 19 of fibre pigtail 7, support block 1 is manipulated 4*° °o horizontally until maximum light throughput via waveguides 8, 9 and 10 is obtained at 4o4*•* S light receivers (not shown) coupled to fibre pigtails 5 and 6. Ledge 24 may also be in the form of a separate base plate extending from and attached to waveguide chip 11.

°o.o°i SThe ends of the aligned fibre pigtails are fixed in positior by an index-matching adhesive or impressed into a silicone index matching membrane over which an adjesive epoxy has been deposited.

The thickness of the silicon substrate S (Figure 1) may vary from chip to chip due to the fact that at the present time silicon substrates from which the chips are fabricated have a relatively large tolerance. Typically, the substrate thickness is 350 um. Therefore height y of support 1 may not coincide precisely with the distance y between the base of substrate S and the centre of layer S2 with every chip. This may hamper precise alignment. On the other hand, the thickness of layers S2 and S3 is very

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precise, typically 0.1, and therefore the distance from the top surface of S3 to the centre of layer S2 is known. Therefore if, after vertical alignment described in relation to Figure 2, the support block 1 complete with affixed pigtails and the waveguide chip 11 are inverted and placed on a grooved datum chip 25 as shown in Figure 4, very precise alignment can be accomplished. After the inverted block and chip are placed on the datum chip horizontal alignment is carried out by the method described in relation to Figure 3. Thereafter block 1 and chip 11 are affixed to datum chip 25 in a known manner and potted in a suitable package. The grooves in datum chip 25 accommodate the upper parts of the affixed pigtails.

The means by which the core centres of the fibre pigtails supported in support block 1 are adjusted is not limited to the optical grating and TV camera arrangement described in relation to Figure 2. Other arrangements may be adapted by those skilled in the art. For example, an arrangement of semiconductor photo-sensors may be utilised, such as, for example, photo-transistors or photo-diodes whose lens' are arranged to detect when the core centre of a rotating fibre pigtail is at height y and at the same side of the vertical plane bisecting the vertex of the supporting groove.

It is envisaged that such sensors could be operatively coupled to a stepping motor arrangement to controllably rotate the fibre optic pigtails to position their cores automatically vis-a-vis the waveguide end centres.

Although the waveguide chip 11 of the preferred embodiment described above is in the form of a passive optical element, the present invention also envisages chips incorporating, in addition to waveguides, active elements coupled thereto.

While the present invention has been described with regard to many particulars it is understood that equivalents may be readily substituted without departing from the scope of the invention.

Claims (22)

1. A method of aligning a plurality of optical fibre pigtails with respective ends of a plurality of buried channel planar waveguides buried in a layer on a substrate of a waveguide chip, the centres of at least two adjoining planar waveguide ends being spaced from each other by a first distance, and the centres of said waveguide ends being at a height from a first surface of said substrate extending in a plane parallel to said planar waveguides by a second distance, said method comprising the steps of: a. Support on support means each said optical fibre pigtail in a parallel spaced relationship so that said centres of the optical fibre pigtail ends are spaced by said first distance and at a height from a reference surface on said support means corresponding to said second distance; b. Launch light into the supported optical fibre pigtails to illuminate, said optical fibre pigtail cores; c. Rotate each supported optical fibre pigtail into a position where its illuminated core centre is spaced from said reference surface by said second distance; d. Restrain said optical fibre pigtails in said position in the support means; e. Interface said ends of the fixed optical fibre pigtails with the said waveguide ends; f. Launch light into one optical fibre pigtail and sense light energy at the opposite end of at least one other optical fibre pigtail optically coupled to said one optical fibre pigtail; g. Align core centres of said optical fibre pigtail ends with said waveguide ends :o by adjusting lateral location of said support means for maximum level of sensed o light energy. h. Fix the aligned fibre pigtails in the so aligned position.

2. A method as claimed in claim 1, wherein the step of interfacing said ends of the S fixed optical fibre pigtails with the said waveguides includes locating said reference surface of said support means on a surface common to the bottom surface of said substrate whereby the ends of the fixed optical fibre pigtails are interfaced with said waveguides.

3. A method as claimed in claim 2, wherein said surface common to said bottom surface of the substrate is a surface extending from said substrate.

4. A method as claimed in claim 1, wherein the step of interfacing said ends of the fixed optical fibre pigtails with said waveguides includes inverting said support means M/ 8 supporting the fixed optical fibre pigtails as well as the waveguide chip, and supporting the inverted support means and inverted waveguide chip on a datum support. A method as claimed in claim 4, includign the step of fixing said support means and said waveguide chip to said datum support after the aligned pigtails are fixed.

6. A method as claimed in any one of the preceding claims, wherein the optical fibre pigtails are fixed in said position in the support means by an adhesive.

7. A method as claimed in any one of the preceding claims, wherein said adhesive is UV-cured epoxy.

8. A method as claimed in any one of the preceding claims, including the step of fixing the ends of the laterally aligned optical fibre pigtails to respective waveguide ends with an index-matching adhesive or impressed into a silicone index-matching membrane, over which an adhesive epoxy has been deposited.

9. A device for aligning a plurality of optical fibre pigtails with respective ends of a plurality of buried channel planar waveguides buried in a layer on a substrate of a Swaveguide chip, the centres of at least two adjoining planar waveguide ends being spaced from each other by a first distance, and the centres of said waveguide ends being at a height from a first surface of said substrate extending in a plane parallel to said planar waveguides from said substrate by a second distance, said device comprising a support means arranged to support each said optical fibre pigtail in a parallel spaced relationship so that said centres of the optical fibre pigtails ends are spaced by said first distance and at a height from a reference surface on said support means corresponding to said second distance, means to launch light into the supported optical fibre pigtail cores, comparator means arranged to compare the position of as illuminated core centre of each optical fibre pigtail with a reference corresponding to said second distance, said illuminated core centre being brought to said second distance by rotation of said fibre optic pigtail and then laterally aligned with said waveguide centres, and fixed thereto. A device as claimed in claim 9, wherein said support means comprises a planar block having a top surface, a bottom surface and at least one side wall, said top surface being provided with at least one group of parallel grooves of a first predetermined depth and of a predetermined spaced relationship.

11. A device as claimed in claim 10, wherein said bottom surface is provided with at least one group of parallel grooves of a second predetermined depth.

12. A device as claimed in claim 10 or 11, wherein each other group of parallel grooves on said top surface and said bottom surface has a different predetermined CO i Z i. V depth.

13. A device as claimed in claim 12, wherein some groups of parallel grooves lie in a plane normal to other groups of parallel grooves.

14. A device as claimed in any one of claims 10 to 13, wherein said planar block is made of glass. A device as claimed in any one of claims 10 to 14, wherein the distance between the centres of two adjoining grooves corresponds to said first distance.

16. A device as claimed in any one of claims 10 to 15, wherein the depth of said grooves is such that the distance between the centre of a supported cptical fibre pigtail and the opposite surface of said planar block corresponds to said second distance.

17. A device as claimed in claim 16, wherein the depth of said grooves is such that the centre of a supported optical fibre pigtail lies in the same plane as that of the gooved surface of said planar block. groedsrfc o ai laa°bok S•185. A device as claimed in any one of claims 9 to 17, wherei said comparator means comprises an arrangement of an optical grating and magnifying lens operatively associated with a TV monitor screen means, whereby illuminated core centres of related fibre-optic pigtails are imaged on said monitor screen means for setting said second distance and positioning such core centres on the same side of their associated S° waveguide end centres.

19. A device as claimed in any one of claims 9 to 17, wherein said comparator means comprises an arrangement of semiconductor optical sensors operatively coupled to indicator means whereby said sensors optically detect when said illuminated -ore centre of a rotating optical fibre pigtail is spaced from reference surface by said first distance and on the same side of its associated waveguide end centre, whereupon said indicator means provides an indication. A device as claimed in claim 19, wherein said semiconductor optical sensors are photo-transistors and/or photo diodes.

21. A device as claimed in claim 19 or 20, wherein said semiconductor optical sensors are operatively coupled to stepping motor means arranged to controllably rotate said fibre optic pigtails to position their cores automatically vis-a-vis the said waveguide end centres.

22. A device as claimed in any one of claims 10 to 21, wherein a planar pad of resilient material is arranged on at least part of the surface of said planar block in whose grooves are supported optical fiore pigtails, for holding said optical fibre pigtails in the I .A grooves during rotation.

23. A method as claimed in any one of claims 1 to 8, wherein said substrate incorporates active components.

24. A fibre-optic device including buried channel planar waveguides to which optical fibre pigtails are attached by the method claimed in any one of claims 1 to 8, and claim 23. A fibre-optic device as claimed in claim 24, wherein said device is a fibre-optic coupler.

26. A fibre-optic device as claimed in claim 24, wherein said device is a waveguide division multiplexer or demultiplexer.

27. A method substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings.

28. A device substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings. DATED THIS FOURTEENTH DAY OF DECEMBER 1992 ALCATEL COMPONENTS LIMITED a a ABSTRACT A method and device for aligning fibre-optic pigtails 6 and 7) with buried channel planar waveguides 9 and 10) in a substrate (11). According to the invention the pigtails are laid in grooves 3 and 4) of a support block The depth and spatial relationship of the grooves being such that the centres of the pigtails correspond with respective centres of the waveguide ends 9 and 10). By launching light (15) into opposite ends of the pigtails, the eccentric pigtail cores (17, 18 and 19) can be firstly positioned at a height which corresponds to the horizontal centre of the waveguide ends, and then laterally centred and adhered to the waveguide ends for optimum fibre-to-waveguide coupling. FIGURE 1. o S et *S *o oo* c