WO2002073269A2

WO2002073269A2 - Optical coupling for mounting an optical fibre on a substrate

Info

Publication number: WO2002073269A2
Application number: PCT/GB2002/001042
Authority: WO
Inventors: John Paul Drake; Emma Jane Clarissa Dawnay; Iain Anteney; Christopher James Hurr; Arnold Peter Roscoe Harpin; Darren Martin; Ivan Evans
Original assignee: Bookham Technology Plc
Priority date: 2001-03-09
Filing date: 2002-03-08
Publication date: 2002-09-19
Also published as: WO2002073269A3; GB2373063A; GB0105838D0

Abstract

An optical coupling for mounting one or more fibres (12) on a substrate comprising a fibre block (8) to which each of the fibres (12) is secured and a substantially planar substrate with a recess (7) provided therein, the fibre block (8) being mounted in the recess (7) to mount the fibres on the substrate.

Description

OPTICAL COUPLING FOR MOUNTING AN OPTICAL FIBRE ON A SUBSTRATE

FIELD OF THE INVENTION

This invention relates to an optical coupling for mounting one or more optical fibres on a planar optical substrate and to a method of fabricating such an optical coupling.

BACKGROUND ART

Various ways of optically coupling an optical fibre to an optical component, such as a waveguide, on an optical substrate are known. In some cases, an end of the optical fibre is located in a V-groove formed on the substrate so as to align the fibre with a waveguide integrated on the substrate. This method is satisfactory for single fibres or for a small number of fibres but becomes more difficult to assemble when more fibres are used. In many situations, it is desirable to couple a fibre ribbon which may comprise a large number of fibres, e.g. up to 80 or more, to respective waveguides on an optical substrate.

One method used to achieve this is to mount the ends of the fibres in a fibre block, polish the ends of the fibres so they are co-planar with an external face of the block, polish an external edge of an optical substrate, which has waveguides leading to that edge, such as an optical chip, and mounting the polished external face of the fibre block adjacent the polished edge of the chip so the ends of the optical fibres are in alignment with the ends of integrated waveguides and securing the block to the chip with adhesive. This method requires the edge of the chip to be polished, which creates considerable amounts of debris and which may damage the ends of the waveguides on the chip. Furthermore, the polishing step has to be carried out on each individual chip and so is not well suited to mass-production.

The present invention aims to provide an alternative method of coupling one or more optical fibres to one or more optical components on an optical substrate which alleviates or avoids such problems.

DISCLOSURE OF THE INVENTION

According to a first aspect of the invention, there is provided a method of mounting one or more optical fibres on a substrate comprising the steps of:

securing one or more fibres to a fibre block, forming a recess within a substantially planar substrate and mounting the fibre block within the recess to mount the fibres on the substrate.

According to a second aspect of the invention, there is provided an optical coupling for mounting one or more optical fibres on a substrate comprising a fibre block to which each of the fibres is secured and a substantially planar substrate with a recess provided therein, the fibre block being mounted in the recess to mount the fibres on the substrate.

Preferred and optional features of the invention will be apparent from the following description and from the subsidiary claims of the specification.

The term fibre block, used herein, refers to an arrangement of one or more components or blocks to which the ends of one or more optical fibres are secured. Typically, a fibre block may comprise two components between which the fibres are sandwiched but it may comprise a single component, e.g. a member with one or more V-grooves therein within which the fibre(s) are secured.

The invention will now be further described, merely by way of example, with reference to the accompanying drawings in which;

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an etched hole formed during the fabrication of a coupling according to one embodiment of the invention;

Figure 2 is a perspective view corresponding to Figure 1 at a later stage in the fabrication process;

Figure 3 is a perspective view of a fibre block (shown in expanded view) and a recess into which it is to be mounted;

Figures 4 and 5 are perspective views from different angles of such a fibre block being inserted into such a recess;

Figure 6 is a plan view of the fibre block mounted in the recess;

Figure 7 is a perspective view of part of a fibre block and part of a recess of another embodiment of the invention;

Figure 8 is a plan view of part of a fibre block and part of a recess in a further embodiment of the invention; Figure 9 is a perspective view of a recess having alignment parts therein for use in another embodiment of the invention;

Figures 10 and 1 1 are end views of fibre blocks used in yet further embodiments of the invention;

Figure 1 2 is a schematic side view illustrating one way of aligning a fibre block within a recess;

Figures 1 3A and 1 3B are plan and side views illustrating further ways of aligning a fibre block within a recess, and Figure 1 3C is a side view showing a further modification of the arrangement shown in Figure 1 3B; and

Figure 1 4A is a perspective view, illustrating a yet further way of aligning a fibre block within a recess and Figure 14B is a cross-sectional view taken along line B-B in Figure 14A.

BEST MODE OF CARRYING OUT THE INVENTION

Figure 1 is a schematic diagram showing a plurality of rib waveguides, represented by component 1 in the figure, formed on a silicon-on-insulator (SOI) wafer and a hole 2 etched into the wafer. The hole 2 is etched through the upper silicon layer 3 of the wafer, the underlying SiO₂ layer 4 and into the silicon substrate 5 beneath the SiO₂ layer.

Figure 1 also shows a dicing line 6, which comprises a thin line etched down to the SiO₂ layer. The dicing line 6 assists in the separation of the individual chips by a subsequent sawing process. The dicing line 6 intersects the hole 2 so, after sawing, a recess 7 is formed at the edge of the chip as shown in Figure 2. The hole 2 is formed by first etching though the upper silicon layer 3 which is typically 5-10 microns thick, by a relatively slow, dry etching process to leave a very well defined, flat surface 1 A at the ends of the waveguides 1 . A wet or dry etch is then carried out through the SiO₂ layer 4, which is typically around 0.4 microns thick, followed by a relatively fast, vertical etch through the silicon substrate 5 which may be 500 microns or more in thickness. The fast etch may be carried out by a dry etch process, such as an inductively coupled plasma (ICP) etch process which is capable of etching at a rate of at least 5 microns per minute, and higher. A typical etchant used in this process is sulphur hexa- fluoride. This process forms a vertical surface 5A, i.e. a surface perpendicular to the plane of the wafer. The surface may have a rippled or smooth form depending on the characteristics of the etch process (although it still presents a vertical abutment for receiving a fibre block as described below).

The hole 2 may be formed through the entire thickness of the substrate 5, or it may terminate part way through the substrate (as shown in Figure 3). In the latter case, the base of the recess may be used to support the fibre block 8 (described below) .

Figure 3 shows a perspective view of a recess 7 formed in the side of a chip and a fibre block 8 for mounting therein. The fibre block comprises a base 9 and a lid 10, each provided with V-grooves 1 1 in which the ends of optical fibres 1 2 (with cladding layer removed) are located. The lid 10 is secured to the base 9, e.g. by adhesive, to clamp the ends of the fibres 1 2, therebetween. The end faces of the fibres 1 2 are polished together with an external face of the block 8 to form an optically smooth surface 8A at the end of the fibre block. The fibre block 8, shown in Figure 3, is similar to a conventional design fibre block, which is butted up against a side face of a conventional chip. Other forms of fibre block may, however, be used, e.g. fibre blocks comprising a single element on the surface of which, fibres are secured in V-grooves therein (i.e. a fibre base without a lid or a lid without a base) .

As shown in Figure 3, although they are perpendicular to the plane of the chip, the end faces of the fibres 1 2 and the end faces of the waveguides 1 may be angled, e.g. typically by 3-5 degrees, so they are not perpendicular to the optical axis thereof, in order to reduce problems due to back reflections at the end faces. Other ways of achieving this will be described at a later stage.

Figure 3 also shows, in dashed lines, a ledge 1 3 which may optionally be formed at the mouth of the recess 7, the fibre block being shaped to fit in the space between the ledge 1 3 and the surfaces 1 A and 5A. The ledge 1 3 thus serves to resist movement of the block out of the recess 7, should, for instance, pulling forces be applied along the optical fibres 1 2.

Figure 3 also shows optional cut-outs 1 4 in the inner corners of the recess 7, the function of which will be described below.

The fibre block 8 is mounted in the recess and secured therein by adhesive. The polished end face 8A of the fibre block is preferably butted up against the flat end face 1 A of the silicon layer 3 to provide a low loss optical coupling therebetween. However, in some cases, it may be desirable to leave a small gap between the end faces 8A and 1 A in which case an index-matching compound may be provided in the gap. The fibre block 8 may also be secured within the recess by other suitable means. The optical fibres 1 2 in the fibre block 8 should be aligned with the waveguides 1 on the chip prior to the block 8 being secured in the recess. This may be achieved by active alignment techniques or by passive alignment techniques, further details of which will be given below.

It will thus be appreciated that, whereas in the prior art, a fibre block is butted up against a polished edge face of a chip, the above arrangement allows the fibre block to be butted up against or placed near thereto a flat surface formed in the recess 7. This flat surface may be formed by etching techniques which can be carried out at wafer scale so that a large number of couplings can be fabricated simultaneously and with minimal handling, in contrast to the prior art which required polishing of the edges of chips either on a chip by chip basis or by polishing the edges of stacked chips. Depending on the size of the individual chips, several tens or several hundreds of couplings can be simultaneously fabricated on a single wafer. This provides a dramatic increase in the speed of manufacture and reduces the need for manual handling of the chips. Furthermore, an anti-reflective (AR) coating is preferably applied to the end faces of the waveguides 1 . In the fabrication method described herein a plasma enhanced chemical vapour deposition (PECVD) nitride layer also may be deposited on the end faces immediately after the hole 2 is etched and this can, again, be carried out on a wafer scale.

In addition to the above, the fabrication method described herein avoids the need to polish the edge of the chip. Polishing is an expensive process and is inherently dirty as it produces a considerable amount of debris which can remain on the chip even after washing and tends to degrade the quality thereof. It can also cause damage to the ends of the waveguides so further reducing product yield in a manufacturing process. Whilst, as described above, the etch process used to form the flat face 1 A is relatively slow, the bulk of the depth of the hole 2 is etched by a fast etching process through the silicon substrate 5. The ability to etch this part of the hole relatively quickly ensures that the manufacturing process can be carried out within an acceptable time.

Figures 4 and 5 are perspective views of a fibre block 8 similar to that described above being inserted into a recess 7 at the edge of a chip.

These figures show cut-outs 14 formed at the corners of the recess 7. The cutouts 1 4 can be formed during the etching of the hole 2 by appropriate shaping of the mask through which the hole 2 is etched and are provided for a number of reasons. Firstly, when it is desired to butt face 8A of the fibre block 8 against the end face 1 A of the waveguides 1 , it is important that the surface at the inner end of the recess 7 is sufficiently flat to permit this. As there is a tendency for the corners of the recess 7 to be slightly rounded, the material in these corners may prevent the fibre block 8 being fully inserted into the recess. The formation of the cut-outs 14 avoids the possibility of such material, or debris from the etching process, remaining in the corners and interfering with the positioning of the fibre block 8. An alternative to this would be to ensure that the width of the surface is sufficiently large so the flat portion thereof, between any rounding of the corners thereof, is wider than the end face 8A of the fibre block 8.

The cut-outs 1 4 also improve the visibility of the fibre block 8, so making it easier to actively align the fibre block 8 with the waveguides. The cut-outs 14 also provide reservoirs for adhesive, e.g. for receiving excess adhesive squeezed out between faces as they are pushed together. Figure 6 shows a plan view of a modified version of the arrangement, shown in figure 5 in which the rib waveguides 1 terminate in a spacer region 1 A. This spacer region serves two functions, it accommodates any misalignment in the masking process when the recess 7 is etched and also serves as a T-bar as described further in WO99/66360, whereby the rounding effect produced by the manufacturing process, e.g. etching, used to form the end faces of the rib waveguides 1 does not affect the flatness of the portion of the end face 1 A through which the majority of the light is transmitted. In this embodiment, the fibre block 8 is shown to be of similar width to the recess 7 so as to be a close fit therein. The close fit of the fibre block 8 within the recess 7 may be used to align the block laterally, i.e. in a direction parallel to the plane of the chip but perpendicular to the optical axis of the waveguides 1 . Alternatively, the recess 7 may be made wider than the fibre block 8 but arranged so that contact between one side face of the block 8 and one side face of the recess 7 provides passive alignment in the lateral direction between the optical fibres 1 2 and the waveguides 1 . Vertical alignment of the fibre block 8 may be achieved by seating the block on a base of the recess 7 (if the recess does not extend all the way through the chip or by active alignment techniques).

It should be appreciated that in the figures described above, the waveguides are shown as extending perpendicular to the edge of the chip. However, if the end faces of the waveguide and/or the optical fibres are inclined to reduce back reflections, some refraction will occur at these faces which may require the optical axis of the optical fibres 1 2 and waveguides 1 to be inclined to each other, e.g. by a few degrees.

Figure 7 shows a perspective view of part of the end surface of the recess 7 and of the fibre block 8. In this case, instead of angling the entire end face of the recess 7 as shown in Figures 3 and 6, only portions at the end of each individual waveguide 1 are angled so a series of saw-tooth shaped recesses 7A are formed in the end face of the recess 7. The saw-tooth shaped recesses 7A may also be formed by modifying the shape of the lithographic mask used to form the hole 2. The end face 8A of the fibre block 8 is butted up against flat portions 7B of the end face of the recess 7 between each of the saw-tooth shaped recesses 7A. If desired, index-matching material may be provided in the gaps between the ends of the waveguides 1 and the end face 8A of the fibre block caused by the saw-tooth shaped recesses 7A.

The arrangement shown in Figure 7 has a number of advantages. Firstly, if the end of the fibre block 8 is incorrectly angled due to manufacturing tolerances in the arrangement shown in Figures 3 and 6, a gap of varying width is formed between the end face 8 A and the end of the recess 7. With the arrangement shown in Figure 7 the end of the fibre block 8 need not be angled so this possible source of error is avoided. Secondly, if the fibre block is of appreciable width (it may comprise many fibres side by side), the arrangement shown in Figures 3 and 6 would require the recess to extend a considerable distance into the chip and thus use up valuable chip area. With the arrangement shown in Figure 7, the recess 7 extends the same distance into the chip irrespective of the width of the fibre block 8.

Figure 8 is a schematic plan view of an alternative arrangement in which a plurality of fibre blocks 8 are used, each having an inclined end surface 8A so, together, they present a saw-toothed shaped end face to the waveguides 1 on the chip. In addition, the end face of the recess 7 may be flat (as shown in Figure 8) or saw-toothed (as shown in Figure 7) .

Figure 9 illustrates another way of ensuring lateral alignment between the optical fibres within the fibre block 8 and the waveguides 1 . During the formation of the recess 9, two elongate projections or posts 1 6 are left in the bottom of the recess in known positions. A fibre block 8 with slots or holes in corresponding positions can then be fitted over the projections 1 6. This method may also be used to determine the location of the fibre block in a direction parallel to the optical axis of the waveguides 1 (particularly if it is desired to leave a gap between the end face of the fibre block 8 and the end faces of the waveguides) . If the projections 1 6 are tapered along their length, perpendicular to the plane of the wafer, and fit into tapered slots or holes, they can also be used to align the fibre block in the vertical direction, i.e. perpendicular to the plane of the chip.

In a further arrangement providing for both horizontal and vertical alignment, metal locating pins which project from the end face of the fibre block may be provided to fit into corresponding features provided on the chip. Figure 1 0 shows an end view of a fibre block 8 showing three optical fibres 1 2 located between V-grooves 1 1 formed in the base 9 and lid 1 0 thereof and two locating pins 1 7 similarly located between U or V-grooves 1 8 formed in the base 9 and the lid 10 thereof. When the fibre block 8 is fitted within the recess 7, the locating pins 1 7 projecting therefrom are located in additional V-grooves (not shown) provided on the surface of the chip, the positions of which may be defined by the same mask used to define the positions of the waveguides 1 , so they are automatically formed in known positions relative to each other.

With the arrangement shown in Figure 1 0, the locating pins 1 7 have to be inserted into the fibre block 8 after the end face 8A has been polished. The pins 1 7 thus have to be inserted into the holes formed by the pairs of grooves 1 8 or the lid 1 0 removed and replaced after insertion of the pins 1 7. Figure 1 1 shows a further arrangement in which a bridge 1 9 is fitted over the lid 1 0, the grooves 1 8 in this case being formed between the bridge 1 9 and the base 9. The bridge 1 9 can be located over the lid 10 to hold pins 1 7 in place after the end face 8A of the fibre block 8 has been polished without disturbing the lid 1 0.

Figure 1 2 is a schematic diagram illustrating a further method of aligning the fibre block in the vertical direction relative to the chip. In this arrangement the lid 10 is arranged to extend beyond the base 9 in at least one direction. The underside of projecting portion 10A of the lid 1 0 may then be located on the surface of the chip. The projecting portion 1 0A may project from the front and/or sides of the fibre block 8 and may be arranged to sit on the upper surface of the chip or on the base of a further recess provided on the chip. The projecting portion 1 0A may also be provided by the bridge 1 9 shown in Figure 1 1 rather than the lid 10.

Figure 1 3A shows a plan view of such an arrangement and Figure 1 3B a front view thereof from the direction B shown in Figure 1 3A (the fibre block 8 is shown in dashed lines in Figure 1 3A for clarity). A further recess 7C is provided on each side of the recess 7, each further recess 7C being in the form of a step at each sides of the recess 7. As shown, a base 7D of each step 7C is used to align the fibre block in a vertical direction. A side face 7E of one step may also be used to align the fibre block 8 laterally. With such an arrangement, the steps 7C may be formed before or after etching of the recess 7. Preferably, their positions are defined by the same mask used to define the waveguides, thus, the side face 7E can be accurately formed in a known position relative to the waveguides 1 .

As shown in Figure 1 3C, a further extension 1 0B may be added to the lid 10 so that the underside thereof may be adhered, using adhesive 20, to the chip at a position away from the surfaces 7C, 7D, used for alignment purposes. The adhesive 20 is preferably located in a further recess 7F, formed in the upper surface of the chip as shown. A similar projection (not shown) may be provided on the other side of the fibre block 8.

The location of one or more projecting portions 10A and 10B on the fibre block lid 10 also helps to strengthen the joint between the fibre block 8 and the chip.

Figure 14A is a schematic perspective view, illustrating a further method of aligning the fibre block 8 in the vertical direction relative to the chip as well as providing lateral alignment between the fibres held within the fibre block 8 and the waveguides 1 . Projecting portions 10A, provided at each side of the lid 10 of the fibre block 8, are seated on the upper surface of the chip. V-grooves are etched in the underside of portion 10A of the lid 10 of the fibre block 8, providing pyramidal (or frusto-pyramidal) recesses 22 therein and corresponding pyramidal (or frusto-pyramidal) recesses 22 are provided on the upper surface of the chip.

Figure 1 4B is a cross-sectional view along line B-B of Figure 1 4A and shows the corresponding pairs of pyramidal (or frusto-pyramidal) recesses 22, with a ball 23, e.g. of glass, held therebetween, which locates the pyramidal (or frusto- pyramidal) recesses in alignment with each other and thus laterally align the lid 10, and hence the fibres 1 2, relative to the rib waveguides 1 in directions parallel to the plane of the chip. The pyramidal (or frusto-pyramidal) recesses 22 on the chip may be formed before or after the etching of the recess 7. Preferably the positions of the pyramidal (or frusto-pyramidal) recesses 22 are defined by the same mask used to define the waveguides 1 . Thus, the pyramidal recesses (or frusto-pyramidal) 22 on the chip can be accurately formed in known positions relative to the waveguides 1 . It will be appreciated that the recesses 22 need not have a square base but can be etched so as to have an elongated base and thus provide alignment in one direction only, parallel to the plane of the chip. Such elongate recesses 22 may be provided either on the chip or on the lid 10, or on both, to provide this form of alignment. The ball 23 may be replaced by some other suitably shaped component.

It will be appreciated that other forms of locating means may be provided for locating the fibre block 8 within the recess 7 and aligning the fibre block 8 relative to the waveguides 1 . The fibre block 8 may also hold a different number of fibres from one up to 8 or more. Alternatively, a plurality of fibre blocks 8 may be provided, one for each group of fibres, e.g. 2, 4, 8 or more fibres (as shown in Figure 8).

The rib waveguides 1 are preferably provided with tapered portions (not shown) at the end thereof as described further in US61 08478.

A fibre block may also be mounted within a recess as described above, to couple optical fibres to other forms of waveguides or other optical components, e.g. directly to a light emitter or a light detector, provided on the chip.

The optical coupling described above thus provides an alternative method of coupling optical fibres to a substrate which enables the couplings to be mass- produced whilst at the same time providing a low loss and robust coupling between the fibres and one or more optical components on the substrate.

Claims

1 . A method of mounting one or more optical fibres on a substrate comprising the steps of: securing one or more fibres to a fibre block, forming a recess within a substantially planar substrate and mounting the fibre block within the recess to mount the fibre(s) on the substrate.

2. A method as claimed in claim 1 , comprising the steps of:

mounting the end of each fibre in the fibre block and arranging for the end face of each fibre to be substantially co-planar with an external face of the block;

processing the substrate to form the recess with a substantially flat surface therein, said flat surface communicating with one or more optical components on the substrate and being substantially perpendicular to the plane of the substrate; and

mounting the fibre block to the substrate with said external face thereof adjacent said substantially flat surface with the end face of each fibre aligned with a respective optical component so as to provide optical coupling therebetween.

3. A method as claimed in claim 1 or 2 in which the recess is formed by etching a hole in a substrate and dividing the substrate along a line which intersects said hole.

4. A method as claimed in claim 1 , 2 or 3 in which the substrate comprises a silicon-on-insulator wafer comprising a layer of silicon separated from a supporting substrate by an insulating layer, the recess process being formed by a first, relatively slow etching process through the silicon layer and a second, faster etching process through the silicon substrate.

5. A method as claimed in claim 4 in which the first etching process comprises a dry etching process, preferably using an etchant such as sulphur hexa-fluoride.

6. A method as claimed in claim 4 or 5 in which the second etching process comprises an inductively coupled plasma etch.

7. A method as claimed in any preceding claim in which the recess is formed through the entire thickness of the substantially planar substrate.

8. A method as claimed in claim 2 or any claim dependent thereon in which the fibre block is aligned so as to provide a low loss optical coupling between the respective optical fibres and optical components and is then secured in position within the recess.

9. A method as claimed in claim 8 in which alignment pins are provided in the fibre block which are located against alignment features provided on the substrate.

1 0. A method as claimed in claim 8 in which the fibre block comprises a projecting portion which is located against one or more alignment surfaces on the substrate.

1 1 . A method as claimed in claim 1 0 in which one of the alignment surfaces comprises a major surface of the planar substrate or a surface parallel thereto.

1 2. A method as claimed in claim 1 0 or 1 1 in which one of the alignment surfaces comprises a surface perpendicular to the plane of the substrate but substantially parallel to the optical axis of the optical fibre(s).

1 3. An optical coupling for mounting one or more optical fibres on a substrate comprising a fibre block to which each of the fibres is secured and a substantially planar substrate with a recess provided therein, the fibre block being mounted in the recess to mount the fibres on the substrate.

14. An optical coupling as claimed in claim 1 3 in which each of the optical fibres is mounted in the fibre block with an end face thereof substantially co-planar with an external face of the block and in which the recess comprises a substantially flat surface in communication with optical component(s) on the substrate and substantially perpendicular to the plane of the substrate, the fibre block being mounted to the substrate with said external face adjacent said flat surface with the end face of each fibre aligned with a respective optical component so as to provide optical coupling therebetween.

1 5. An optical coupling as claimed in claim 1 3 or 1 4 in which the fibre block comprises a base and a lid with the fibres held therebetween.

1 6. An optical coupling as claimed in claim 1 3, 1 4 or 1 5 in which the recess is provided at an edge of the substrate.

1 7. An optical coupling as claimed in claim 14 in which a cut-out is provided in corners of the recess at each end of said flat surface.

1 8. An optical coupling as claimed in any of claims 1 3 to 1 7 in which the normal to the end face of each of the fibres is inclined to the optical axis thereof.

1 9. An optical coupling as claimed in claim 1 4 or any claim dependent therein in which the optical component(s) provided on the substrate comprises one or more optical waveguides which extend to said flat surface.

20. An optical coupling as claimed in claim 1 9 in which the normal to the end face of each waveguide is inclined to the optical axis thereof.

21 . An optical coupling as claimed in claim 20 in which the normal to said flat surface is inclined to the optical axis of each waveguide.

22. An optical coupling as claimed in claim 20 in which a cut-out is formed in said flat surface at the end of each waveguide, one side of the cut-out providing a surface the normal of which is inclined to the optical axis of the waveguide.

23. An optical coupling as claimed in any of claims 1 3-22 in which alignment features are provided on the fibre block and the substrate to provide passive alignment therebetween.

24. An optical coupling as claimed in claim 23 in which the fibre block is provided with alignment pins and the substrate comprises grooves in which the pins are located.

25. An optical coupling as claimed in claim 23 in which the fibre block comprises a projecting portion which is located against one or more alignment surfaces in the substrate.

26. An optical coupling as claimed in claim 25 in which the substrate comprises a first alignment surface parallel to the plane of the substrate.

27. An optical coupling as claimed in claim 25 or 26 in which the substrate comprises a second alignment surface, which is perpendicular to the plane of the substrate and substantially parallel to the optical axis of the optical fibres.

28. An optical coupling as claimed in claim 25 in which recesses are provided in the projecting portion at a surface of the substrate and a ball positioned in the respective recesses to locate the projection relative to the surface of the substrate.

29. An optical coupling as claimed in claim 23 in which two projections are provided in the recess extending perpendicular to the plane of the substrate and the fibre block has holes which fit over the projections.

30. An optical coupling as claimed in any of claims 1 3-29 comprising a plurality of fibre blocks within the same recess.

31 . An optical coupling as claimed in any of claims 1 3-30 in which the substrate comprises a layer of silicon separated from a supporting substrate by an insulating layer.

32. An optical coupling as claimed in claim 1 4 and 31 in which the optical components comprise one or more rib waveguides.

33. A method of mounting one or more optical fibres on a substrate substantially as hereinbefore described with reference to one or more of the accompanying drawings.

34. An optical coupling for mounting one or more optical fibres on a substrate substantially as hereinbefore described with reference to and/or as shown in one or more of the accompanying drawings.