GB2381084A

GB2381084A - Bent optical fibre located on substrate and connecting to optical device

Info

Publication number: GB2381084A
Application number: GB0130338A
Authority: GB
Inventors: Stephen Jeffrey Tyler
Original assignee: Bookham Technology PLC
Current assignee: Lumentum Technology UK Ltd
Priority date: 2001-12-19
Filing date: 2001-12-19
Publication date: 2003-04-23
Also published as: GB0130338D0

Abstract

An apparatus for connecting an optical fibre 4 to an optical device has a substrate which can be in the form of optical chip 1 mounted on a base 2 with a top surface having locating means such as V-groove 7 for locating the optical fibre on the substrate and a substantially rigid guide such as ferrule 20 along which the optical fibre extends and which is located remote from the locating means and at an angle r with respect to the top surface. The optical fibre therefore extends substantially level between an exit region 34 of the guide and the locating means 7, and it is held in the locating means as a result of the forces introduced at the bend in the fibre at the exit region of the guide. The end optical fibre 4 is stripped of cladding 11, 12 prior to insertion into ferrule 20.

Description

APPARATUS AND METHOD FOR CONNECTING AN OPTICAL FIBRE TO AN OPTICAL DEVICE The present invention relates to an apparatus and method for connecting an optical fibre to an optical device.

It is known to connect an optical fibre to an optical device by mounting the end of the fibre in a V-groove provided in the face of an optical chip in order to align the optical fibre with a waveguide on the chip. The fibre is conventionally secured in the V-groove by adhesive or solder which can cause misalignment if too much or too little adhesive or solder is used. Such apparatus also suffers from disadvantages arising from solidification of the adhesive or solder or material creep in the adhesive or solder which can both cause movement of the fibre and so disturb the alignment of the fibre with the waveguide.

An alternative solution has been offered in US 6,075, 914 where in attachment means secure the optical fibre to a position remote from the V-groove so that the fibre is held in a state of elastic deformation to assist in holding the fibre in contact with the locating means without it being secured thereto.

The difficulty with this solution is that it requires high tolerance parts to achieve angles in the requisite position of the fibre. These are difficult and expensive to produce in volume.

It is an aim of the present invention to overcome these difficulties.

According to one aspect of the invention there is provided an apparatus for connecting an optical fibre to an optical device comprising: a substrate having a top surface; locating means for locating an optical fibre on the substrate; and a substantially rigid guide along which the optical fibre extends and which is located remote from the locating means and at an angle with respect to the top surface, wherein the optical fibre extends substantially level between an exit region of the

guide and the locating means, whereby it is held in the locating means as a result of the forces introduced at the bend in the fibre at the exit region of the guide.

A further aspect of the invention provides a method of assembling an optical package, the method comprising: providing a substantially rigid guide along which extends an optical fibre cable comprising an optical fibre and external cladding ; cutting the optical fibre cable at a predetermined distance from a proximal end of the substantially rigid guide; stripping the cladding from at least part of the length of the cut optical fibre cable ; locating the substantially rigid waveguide in an aperture in a base on which is mounted a substrate having locating means, whereby an end of the stripped optical fibre portion is located in the locating means on the substrate.

In the described embodiment, the substantially rigid guide is located within an aperture on a base on which the substrate is mounted. A single guide, for example in the form of a ceramic cylindrical ferrule, which sits against the optical chip enables accurate and easier placing in the package. In the described embodiment, the shape of the ferrule allows for the bend in the fibre as it enters the package to be more gradual, reducing the possibility of the fibre cracking.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings, in which: Figure 1 is a perspective view of the apparatus according to one embodiment of the invention; Figure 2 is a schematic section through the apparatus according to Figure

1 ; Figure 3 is a schematic diagram showing an enlarged plan view of the apparatus of Figure 1; Figure 4 is an enlarged and schematic side view in which certain features have been exaggerated for the sake of explanation ;

Figure 5 is a sectional view through a ferrule with partially stripped optical fibres; Figure 6 is a perspective schematic view of the apparatus according to one alternative embodiment of the invention; Figure 7 is a mathematical profile of a cylinder inclined with respect to a plane ; Figure 8 is a profile of the hole in the substrate in a practical embodiment; and Figure 9 is a section through a ferrule with an eccentrically mounted fibre.

Figures 1 and 2 show a substrate in the form of an optical chip 1 mounted on a base 2, for example of aluminium oxide or aluminium nitride, and an optical fibre 3 for transmitting signals received on an optical fibre cable 4 to an optical device on the optical chip 1, or vice versa. Reference numeral 20 denotes a ceramic ferrule which constitutes a substantially rigid guide for holding the optical fibre 3.

The ferrule is substantially cylindrical and is located on the base 2 with its proximal end 22 in a hole 24 formed in the base 2. This has the effect of locating the ferrule 20 at an angle so that its distal end 26 lies in a plane above the plane of its proximal end 22. This can be seem most clearly in Figure 2. In the preferred embodiment the angle S which is made between the plane of the base 2 and the longitudinal axis of the ferrule 20 is 7 degrees. The ferrule 20 is held in place by one or both of solder 28 to locate it in the hole 24 and a clamp denoted 30 in Figure 2. A cover 32 (illustrated only in Figure 2) is provided to make a hermetic seal with the base 2, an opening 34 being provided through which the ferrule 20 extends. A potentially hermetic seal can be provided around the opening 34 where the ceramic ferrule 20 protrudes.

The optical fibre 3 leaves the proximal end 22 of the ferrule 20 at an exit region denoted 34 in Figure 2. It will readily be appreciated that as a result of the fact that the ferrule 20 is disposed at an angle, a bend is created in the optical fibre 3 at this exit region 34. The forces introduced into the fibre at this bend cause the fibre to be pressed downwards onto the chip 1. Thus, between the exit region 34

and the region where the optical fibre 3 is located on the chip 1, the optical fibre extends substantially level, in fact more or less in the plane of the chip 1.

Figures 3 and 4 illustrate the manner of location of the optical fibre 3 on the chip 1 in more detail. As shown in these figures, the end of the optical fibre 3 is located in a V-groove 7 provided in the surface of the optical chip 1. Figures 3 and 4 also show an optical waveguide 8 on the optical chip 1 with which the optical fibre is to be aligned. The V-groove 7 serves to locate the lateral position of the optical fibre 3, i. e. in a direction perpendicular to the optical axis of the waveguide 8 and the optical fibre 3. In this case, the position of the optical fibre 3 is in a direction perpendicular to the plane of the optical chip 1 and the position of the optical fibre 3 in both directions is perpendicular to the optical axis within the plane of the optical chip 1.

As can be seen more clearly in Figure 4, a bend is introduced into the optical fibre 3 at its exit region 34 from the ceramic ferrule 20. This causes the optical fibre 3 to rest horizontal in the groove 7 of the chip 1, held in position by the pressure exerted by the bend in the fibre 3. This pressure assists in holding the end of the fibre 3 in the V-groove 7 by causing a force downwards in the direction towards the bottom of the V-groove 7 and resist movement of the optical fibre 3 out of the V-groove 7 in a direction perpendicular to the plane of the optical chip 1. The end of the optical fibre 3 is thus held within the V-groove 7 without the need for adhesive or solder in the V-groove 7.

The ferrule 20 is located and held in the slot 24 in the base 2 by an adhesive, for example a light cured or heat cured resin, or solder, for example a glass solder, with or without the addition of mechanical means such as a clamp 30. The angle at which the ferrule 20 rests in the slot 24 is determined by the geometry of the slot 24 and as already discussed in the preferred embodiment is such as to lie at an angle of 7 degrees with respect to the plane of the base 2. However, this angle may vary depending on the particular geometry of the chip, base and the

design requirements. In particular a variation between 10 and 30 may be appropriate.

This manner of securing an optical fibre 3 in the groove 7 also avoids misalignment problems associated with the use of adhesive or solder in the V- groove 7. In addition, it helps avoid long term stress corrosion problems with the optical fibre 3 as the optical fibre 3 is not held rigidly, other than with respect to the ceramic ferrule 20. Thus, this allows for differential thermal expansion with the base 2 without inducing stresses and strains in the optical fibre 3. That is, the end of the optical fibre 3 on the, optical chip 1 is free to move in a direction along the length of the optical fibre 3 as the optical fibre 3 expands and contracts without stresses or strains being induced therein. This helps increase the long term reliability of the apparatus.

Moreover, the fixing of the ceramic ferrule and ceramic requires no solder/epoxy.

Figure 5 is a schematic cross-sectional view showing the ceramic ferrule 20 prior to its location in the base 2. The fibre cable 4 comprises the optical fibre 3, an inner sleeve or coating 11 and an outer coating or jacket 12. Both of the coatings 11 and 12 are formed of plastic materials. The inner coating 11 may, for instance, be formed of a UV cured acrylate and the outer coating 12 may be polypropylene or other plastic materials having similar properties. The coatings 11 and 12 are rigidly secured within the ceramic ferrule 20. Preparation of the ferrule and fibre prior to location in situ on the base 2 will now be described. The ferrule 20 is initially provided with an extent of fibre cable 4 extending from it. The fibre cable 4 is cleaved by a laser or other means at a distance D measured from the end of the ferrule. Part of the length of the exposed optical fibre 4, denoted I in Figure 5, is stripped of its inner and outer coatings 11,12.

As shown in exaggeration in Figure 5, the cleaved angle of the fibre 3 is not in a plane perpendicular to the longitudinal axis of the fibre 3. Instead it lies at an angle to that plane, as denoted by the cleave line X-X in Figure 5. That angled

face of the fibre can be located upwards, downwards or sideways in the V-groove 7 by appropriately rotating the ferrule 20 before it is secured in the slot 24.

If the ferrule were providing a connector core, the back face of the ferrule 20 can be polished, also to an angle if desired. When the angle 0 is 7 degrees, the angle of polishing of the back face can be 7 degrees to help reduce back-reflection.

Once the ferrule/fibre combination has been made as discussed above, in assembly of the apparatus, the ceramic ferrule 20 is located and secured in its slot 24. The distance D between the proximal end 22 of the ferrule 20 and the cleaved end of the optical fibre 3 is such that this locates the optical fibre 3 in the correct position in the V-groove 7. That is, there will typically be a gap of around 10 microns between the end of the optical fibre 3 and the end of the waveguide 8.

It will readily be appreciated, that the location of the hole 24 with respect to the chip 1 on the base 2, its geometry and that of the ferrule/fibre assembly accurately predetermine this gap such that assembly is more reliably accurate.

It will be noted that the waveguide 8 illustrated in Figure 3 is shown overhanging the end of the V-groove 7 (which has an inclined end wall). This form of connection is suitable for a rib waveguide formed on a silicon-on-insulator chip but it will be appreciated that other arrangements and other types of optical chip may be used.

Other forms of locating means may be provided on the chip in place of the Vgroove 7, for example a step or one or more pedestals against which the side of the optical fibre 3 abuts.

Although the description given above relates to the alignment of an optical fibre with a waveguide, the fibre may also be arranged to connect with other forms of optical devices, for example a light emitter or a light receiver.

Multiple fibres may be connected in a similar way. Figure 6 shows an embodiment in which a plurality of fibres 3a... 3n are located in a common ferrule 20 which is secured to the base 2 in a manner as has been discussed earlier. In this case, it will be appreciated that the cleave angle of each optical fibre 3a... 3n will have to be adjusted prior to assembly of the ferrule 20 with respect to the base 2 to meet the individual cleave angle requirements.

Figure 7 shows the profile of an idealised hole in a substrate which would accommodate a cylinder inclined at an angle and supported by the hole. In practice, what is required is to support the hole 20 at predetermined locations as indicated by the profile of Figure 8 wherein the inwardly extending lugs 50 and 52 are used to support the ferrule.

The inwardly extending lugs 50 are set to a dimension to match that of the ferrule 20. Ideally, the optical fibre 3 is located centrally within the ferrule 20 as denoted by the cross at the centre of Figure 9. However there will be cases where sometimes the fibre is mounted eccentrically. If this happens, this can be used to advantage by rotating the ferrule 20 about its axis after location to optimise the power output prior to fixing the ferrule in place.

Claims

CLAIMS :

1. An apparatus for connecting an optical fibre to an optical device comprising : a substrate having a top surface; locating means for locating an optical fibre on the substrate; and a substantially rigid guide along which the optical fibre extends and which is located remote from the locating means and at an angle with respect to the top surface, wherein the optical fibre extends substantially level between an exit region of the guide and the locating means, whereby it is held in the locating means as a result of the forces introduced at the bend in the fibre at the exit region of the guide.

2. An apparatus according to claim 1, wherein the substrate is mounted on a base comprising an aperture in which the substantially rigid guide is located.

3. An apparatus according to claim 1 or 2, wherein the angle at which the guide is located lies in the range 10 to 300.

4. An apparatus according to any preceding claim, wherein the angle at which the guide is located is 7 degrees.

5. An apparatus according to any preceding claim, wherein the locating means comprises a groove formed in the top surface of the substrate.

6. An apparatus according to claim 5, wherein the groove is a V-groove.

7. An apparatus according to claim 2, or any of claims 3 to 6 when dependent thereon, wherein the substantially rigid guide is secured in the aperture by securing means.

8. An apparatus according to any preceding claim, wherein the substrate comprises an optical chip.

9. An apparatus according to any preceding claim, wherein the substrate comprises a silicon-on-insulator chip.

10. An apparatus according to claim 2, or any of claims 3 to 9 when dependent thereon, further comprises a cover which provides with respect to the base a hermetic package for the substrate.

11. An apparatus according to any preceding claim, wherein the substantially rigid guide comprises a ceramic ferrule.

12. An apparatus according to any preceding claim, wherein the substantially rigid guide is cylindrical, with the optical fibre extending along its axis.

13. An apparatus according to any preceding claim, in which a plurality of optical fibres extend along the length of the substantially rigid guide such that they are located at adjacent spaced locations on the substrate.

14. A method of assembling an optical package, the method comprising: providing a substantially rigid guide along which extends an optical fibre cable comprising an optical fibre and external cladding ; cutting the optical fibre cable at a predetermined distance from a proximal end of the substantially rigid guide; stripping the cladding from at least part of the length of the cut optical fibre cable ; locating the substantially rigid waveguide in an aperture in a base on which is mounted a substrate having locating means, whereby an end of the stripped optical fibre portion is located in the locating means on the substrate.

15. A method according to claim 14, wherein the optical fibre cable is cut by laser cleaving.

16. A method according to claim 14 or 15, wherein the optical fibre is cut at an angle.