GB2377276A

GB2377276A - Reinforcing the fibre when mounting an optical fibre cable to an optical device

Info

Publication number: GB2377276A
Application number: GB0116032A
Authority: GB
Inventors: Darren Lee Martin
Original assignee: Bookham Technology PLC
Current assignee: Lumentum Technology UK Ltd
Priority date: 2001-06-29
Filing date: 2001-06-29
Publication date: 2003-01-08
Also published as: GB0116032D0; WO2003003081A2; AU2002310544A1; WO2003003081A3

Abstract

An assembly (100) comprises an optical device (6), a housing (2a, 8) in which the optical device is housed and an optical fibre cable (10) which extends through a passageway (11) in the housing to be coupled to the optical device. The passageway has an entrance (7) on an exterior side of the housing and an exit (13) on an interior side of the housing. The optical fibre cable has a first section with a first transverse dimension (Fig 4, d2, d3) on the entrance side of the passageway, a second section with a second transverse dimension (Fig 4, d1) which is less than the first transverse dimension in the passageway and a third section with a third transverse dimension (d4) which is greater than the second transverse dimension between the exit of the passageway and the optical device. The third section can be made greater by applying sheath 102 so as to reinforce it.

Description

IMPROVEMENTS IN MOUNTING AN OPTICAL FIBRE CABLE TO AN OPTICAL DEVICE Field of the Invention The present invention relates to improvements in mounting an optical fibre cable to an optical device, for instance an optical chip.

Background of the Invention An optical fibre cable typically comprises a central optical fibre enclosed by a sheath comprising one or more layers of a plastics material. The optical fibre itself has a central core surrounded by an outer cladding. The sheath not only protects the optical fibre from damage but also acts to provide a flexible construction.

Various optical chip constructions are known for transmitting, amplifying, receiving and processing optical signals carried by optical fibres. The optical chips may take the form of integrated optical chips, for instance based on a silicon substrate. As the performance of optical chips can be impaired by moisture, it is known to assemble an optical chip to an optical fibre in a hermetically sealed environment. One such assembly is disclosed in WOOO/02079 (Bookham Technology Limited/Yeandle), the contents of which are incorporated herein by reference.

The assembly of WOOO/02079 is shown in FIGURES 1 to 5. As can be seen, the hermetically sealed environment is formed in an outer casing structure 2 which is formed from a material which is impervious to moisture. One such material is KOVAR, a nickel-iron-cobalt metal alloy. The outer casing structure 2 comprises a container part 2a and a lid part (not shown) which are adapted to be sealed together. An integrated silicon optical chip 6 is mounted on a ceramic insulator 4 which in turn is secured to the base of the container part 2a. Such an optical chip is called a silicon-on-insulator chip or SOI for short. Although not shown, the container part 2a ordinarily includes electrically conducting pins for

mounting the casing structure 2 to a printed circuit board and providing pathways for the conduction of electricity to and from the optical chip 6.

The container part 2a includes a tubular extension 2b having a lumen 3 to which is seated a ferrule 8 through a seal 9. The seal 9 may be formed by soldering or through use of an epoxy resin or a glass sealant material.

As shown in FIGURE 2, the ferrule 8 is a sleeve-like element having a lumen 11. The lumen has an entrance 7, an exit 13 and a stepped profile which gives the lumen an enlarged section 14 adjacent the exit 13. The enlarged section 14 of the lumen 11 receives an insert 16 as a push-fit. The insert 16 has a lumen 18 with a narrow diameter do and a countersunk entrance 26. The ferrule 8 and insert 16 are formed from materials which are impervious to moisture. For example, the ferrule 8 may be made from a metal and the insert 16 from a ceramic. The construction of the ferrule 8 is such as to allow an optical fibre 12 of an optical fibre cable 10 to be coupled to the optical chip 6 (see FIGURE 1) whilst maintaining a hermetically sealed environment for the optical chip 6.

The construction of the optical fibre cable 10 is shown in FIGURE 3. The optical fibre 12 of the cable 10 is constituted by a core 28 and an outer cladding 30 and has a diameter d1. The optical fibre 12 is enclosed in a protective jacket or sheath constituted by a pair of acrylic layers 32 and an outer protective buffer layer 34. This give the cable 10 a diameter d3.

Referring to FIGURE 4, as a first step in the process for mounting the optical fibre 12 to the optical chip 6 the buffer layer 34 of the cable 10 is stripped from a distal section L 1 of the cable 10. The acrylic layers 32 are then stripped from a distal portion L2 of the distal section L 1 to expose the optical fibre 12. The acrylic layers 32 are left over a proximal portion L3 of the distal section L 1 giving the proximal portion L3 a diameter d2 in-between the diameters d1, d3 of the distal portion L2 and cable bulk. It follows that a step 35 is formed between the distal and proximal portions L2, L3.

Turning now to FIGURE 5, after the optical fibre cable 10 has been stripped it is inserted through the entrance 7 of the lumen 11 of the ferrule 8 until the step 35 abuts the countersunk entrance 26 to the insert lumen 18. As will be gathered, the diameter do of the insert lumen 18 is chosen to closely match the diameter di of the optical fibre 12 so that the distal portion L2 forms a close fit in the insert lumen 18. Moreover, the diameter of the ferrule lumen 11 is chosen to match the diameter d3 of the optical fibre cable 10. Seals (not shown) are formed between the insert 16 and the ferrule 11, on the one hand, and the optical fibre 12 and the insert lumen 18, on the other hand, by placing an epoxy adhesive on the step 35 prior to passing the optical fibre cable 10 through the ferrule 8. The epoxy resin is drawn into the respective interfaces through capillary action.

The assembly of the ferrule 8 and the optical fibre cable 10 is then passed into the lumen 3 of the tubular extension 2b of the container part 2a. The ferrule 8 is sealed to the lumen 3 and the optical fibre 12 projecting from the ferrule 8 coupled to the optical chip 6, as shown in FIGURE 1.

While the assembly made known in WOOO/02079 provides good hermetic sealing of the optical chip 6, the optical fibre 12 extending between the ferrule 8 and the optical chip 6 is susceptible to damage due to the protective jacket 32,34 having been stripped off to enable it to pass through the insert 16. Any damage inflicted to the exposed optical fibre 12 can lead to an impairment of its performance.

It is therefore an aim of the present invention to provide an improvement in the mounting of an optical fibre cable to an optical device, e. g. an optical chip.

Summary of the Invention According to a first aspect of the present invention there is provided an assembly comprising an optical device, a housing in which the optical device is housed and an optical fibre cable which extends through a passageway in the housing to be coupled to the optical device, the passageway having an entrance

on an exterior side of the housing and an exit on an interior side of the housing and the optical fibre cable having a first section with a first transverse dimension on the entrance side of the passageway, a second section with a second transverse dimension which is less than the first transverse dimension in the passageway, and a third section with a third transverse dimension which is greater than the second transverse dimension between the exit of the passageway and the optical device.

According to a second aspect of the present invention there is provided a method of mounting an optical fibre cable to an optical device housed in a housing provided with a passageway to the optical device, the method comprising the steps of :- providing an optical fibre cable having a distal end; reducing the transverse dimension of a distal section of the optical fibre cable, the distal section including the distal end; inserting the distal section of the optical fibre cable through a lumen of a sleeve element so that a proximal portion of the distal section is positioned in the lumen and a distal portion projects from the lumen ; applying a sheath to the distal portion of the distal section of the optical fibre cable ; positioning the sleeve in the passageway of the housing so that the distal portion of the distal section of the optical fibre cable extends into the housing; and coupling the distal portion of the distal section of the optical fibre cable to the optical device.

Preferred features of the invention are set out in the dependent claims appended hereto.

By way of example, embodiments of the invention will now be described with reference to the accompanying Figures of drawings.

Brief Description of the Figures of Drawings FIGURE 1 is a cross-sectional side view of a prior art assembly in which an optical fibre cable is mounted to an optical chip ; FIGURE 2 is a cross-sectional side view of a ferrule forming part of the assembly shown in FIGURE 1 ; FIGURE 3 is an end view of an optical fibre cable ; FIGURE 4 is a side view of the optical fibre cable after it has been stripped for passage through the ferrule ; FIGURE 5 is a cross-sectional side view of the stripped optical fibre cable mounted in the ferrule ; FIGURE 6 is a cross-sectional side view of an assembly in accordance with the present invention ; FIGURE 7 is an enlarged cross-sectional side view of a part of the assembly of FIGURE 6 ; and FIGURE 8 is an enlarged side view of a part of a modified assembly in accordance with the present invention.

Detailed Description of the Exemplary Embodiments of the Invention In FIGURES 6 and 7 there is shown an assembly 100 in accordance with the present invention. The assembly 100 has many features in common with the prior art assembly illustrated in FIGURES 1 to 5 and the same reference numerals have been maintained for these features.

The principal difference between the assembly 100 of the invention and the prior art assembly is that the central optical fibre 12 extending between the exit 13 of the ferrule 8 and the optical chip 6 is provided with a new sheath 102 of diameter d4 to decrease the risk of it being damaged, e. g. during further processing of this section of the optical fibre 12.

The new sheath 102 can be applied to the optical fibre 12 in a number of different ways. As an example there may be mentioned the following.

Once the optical fibre cable 10 has been sealed in the ferrule 8 as described previously with reference to FIGURES 1 to 5, the section of optical fibre 12 projecting from the ferrule 8 is placed in a mould cavity defined between the mould parts of a mould assembly. A fluid plastics material is injected into the mould cavity to surround the optical fibre 12 and then set to form the new sheath 102 about the optical fibre 12. The plastics material is preferably set by curing with electromagnetic radiation, for example ultraviolet radiation. The mould parts would then need to be transparent to the electromagnetic radiation. For curing by ultraviolet radiation, the mould parts may be made from quartz.

The plastics material of the new sheath 102 is selected to provide similar properties as the original sheath material, namely protection and flexibility.

The new sheath 102 is preferably formed along the length of the section of the optical fibre 12 projecting from the ferrule 8, including the distal end thereof. The portion of the new sheath 102 covering the distal end of the optical fibre 12 is then stripped off for coupling of the exposed distal end of the optical fibre 12 to the optical chip 6. Alternatively, the mould assembly may be such that the distal end of the optical fibre 12 is not re-sheathed to obviate the need for the additional stripping step.

After the new sheath 102 has been applied to the optical fibre 12, the ferrule 8 is sealed in the tubular extension 2b of the container part 2a and the unsheathed distal end of the optical fibre 12 coupled to the optical chip 6.

In the embodiment of the invention shown in FIGURES 6 and 7, the distal end of the optical fibre 12 is mounted in a groove (not shown) etched into the upper surface of the optical chip 6. However, the optical chip 6 may be of a type requiring the'optical fibre 12 to be coupled to it in another way, as will be understood from FIGURE 8.

In the embodiment shown in FIGURE 8 the unsheathed distal end of the optical fibre 12 is mounted in a mounting block 104 after the optical fibre cable 10 is sealed in the ferrule 8. The mounting block 104 may be made from silicon and comprises first and second parts 104a, 104b, the opposed faces of which being secured together and formed with tapered grooves to define an open-ended channel 106 in the mounting block 104 for receiving the distal end of the optical fibre 12. The distal end of the optical fibre 12 is secured in the channel 106 through a suitable adhesive, e. g. epoxy resin. The mounting block 104 is then adhered to a face of the optical chip 6.

The use of the mounting block 104 has particular relevance where the end face 110 of the optical fibre 12 needs to be brought into apposition with an integrated waveguide disposed on the upper surface of the optical chip 6 and having an inlet or outlet adjacent a side face of the optical chip 6. The end faces 108a, 108b of the mounting block 104 are then adhered to the side face of the optical chip 6 to place the end face 110 of the optical fibre 12 in apposition with the inlet or outlet of the waveguide.

Typically, the mounting block 104 would be mounted on the distal end of the optical fibre 12 prior to the optical fibre cable 10 being passed through the tubular extension 2b and the ferrule 8 sealed in place.

As will be understood by the skilled reader in the art, the present invention is not restricted to the exemplary embodiments described above but may be varied in many different ways within the scope of the appended claims. For instance, it is not necessary for the lumen 18 of the insert 16 in the ferrule 8 to be sized so that

the optical fibre cable 10 needs to be stripped down to its central optical fibre 12 to pass through it. The reduction in thickness of the optical fibre cable 10 could, instead, be such as to still leave some of the protective sheath 32,34 around the optical fibre 12 which passes through the insert 16. Moreover, it is not necessary for the ferrule'8 and insert 16 to be used. The lumen 3 in the tubular extension 2b could be shaped to perform the same function as the ferrule 8 and the insert 16.

Although the description of the exemplary embodiments refers to a single optical fibre in an optical fibre cable, the invention also has application to cases where more than one optical fibre is provided in an optical fibre cable.

It will be further understood that the use of reference numerals in the appended claims is purely for illustration and not to be taken as having a limiting effect on the scope of the claims. In addition, the order of the steps in the method claims may be changed and is therefore also not to be taken as limiting.

Claims

1. An assembly (100) comprising an optical device (6), a housing (2a, 8) in which the optical device is housed and an optical fibre cable (10) which extends through a passageway (11,18) in the housing to be coupled to the optical device, wherein the passageway has an entrance (7) on an exterior side of the housing and an exit (13) on an interior side of the housing, wherein the optical fibre cable has a first section with a first transverse dimension (d2, d3) on the entrance side of the passageway, a second section with a second transverse dimension (d1) which is less than the first transverse dimension in the passageway, and a third section with a third transverse dimension (d4) which is greater than the second transverse dimension between the exit of the passageway and the optical device.

2. An assembly according to claim 1, wherein the passageway has a section (18) which has a transverse dimension (do) which is less than the first transverse dimension of the first section of the optical fibre cable.

3. An assembly according to claim 2, wherein the second section of the optical fibre cable has a close fit with the section of the passageway.

4. An assembly according to claim 1,2 or 3, wherein the second section of the optical fibre cable is sealed to the section of the passageway.

5. An assembly according to claim 4, wherein the optical device is hermetically sealed in the housing.

6. An assembly according to any one of the preceding claims, wherein the housing comprises a first part (2a) having a passageway (3) which extends from an outer surface of the first part into the housing and a second part (8) which is sealed in the passageway of the first part and in which is formed the passageway (18) through which the optical fibre cable extends into the housing.

7. An assembly according to any one of the preceding claims, wherein the optical fibre cable has a distal end coupled to the optical device and wherein the optical fibre cable has a fourth section which extends from the third section to the distal end, the fourth section of the optical fibre cable having a fourth transverse dimension which is less than the third transverse dimension.

8. An assembly according to any one of the preceding claims, wherein the optical fibre cable comprises an optical fibre (12) and a sheath (32, 34) which surrounds the optical fibre at least in the first and third sections of the optical fibre cable.

9. An assembly according to claim 8, wherein the second section of the optical fibre cable consists of the optical fibre.

10. An assembly according to claim 8 when appendant to claim 7 or according to claim 9, wherein the fourth section consists of the optical fibre.

11. An assembly according to any one of the preceding claims further comprising a device (104) which attaches the optical fibre cable to the optical device.

12. An assembly according to claim 11 when appendant to claim 7, wherein the device holds the fourth section of the optical fibre cable and is secured to the optical device to appose the distal end of the optical fibre cable to the optical device.

13. A method of mounting an optical fibre cable to an optical device (6) housed in a housing (2a, 8) provided with a passageway (3) to the optical device, the method comprising the steps of :providing an optical fibre cable (10) having a distal end ; reducing the transverse dimension of a distal section (L2, L3) of the optical fibre cable, the distal section including the distal end ;

inserting the distal section of the optical fibre cable through a lumen (11,18) of a sleeve element (8) so that a proximal portion of the distal section is positioned in the lumen and a distal portion projects from the lumen ; applying a sheath (102) to the distal portion of the distal section of the optical fibre cable ; positioning the sleeve in the passageway of the housing so that the distal portion of the distal section of the optical fibre cable extends into the housing; and coupling the distal portion of the distal section of the optical fibre cable to the optical device.

14. A method according to claim 13 comprising the step of reducing the transverse dimension of the distal section so that the proximal portion of the distal section forms a close fit in the lumen of the sleeve element.

15. A method according to claim 13 or 14 comprising the step of sealing the proximal portion of the distal section of the optical fibre cable to the lumen of the sleeve element.

16. A method according to claim 13,14 or 15 comprising the step of sealing the sleeve element to the passageway of the housing.

17. A method according to any one of claims 13 to 16 comprising the step of providing the distal end of the optical fibre cable with a transverse dimension which is less than the transverse dimension of the sheath.

18. A method according to claim 17 comprising the steps of applying the sheath to the whole of the distal portion and subsequently reducing the transverse dimension of the sheath at the distal end.

19. A method according to claim 17 comprising the step of applying the sheath selectively to the distal portion so that the distal end is not sheathed.

20. A method according to any one of claims 13 to 19 comprising the steps of mounting the distal end of the optical fibre cable in a mounting device (104) and securing the mounting device to the optical device.

21. A method according to any one of claims 13 to 20, wherein the optical fibre cable has an optical fibre (12) enclosed in a sheath (32,34) and wherein the sheath is removed from the distal section of the optical fibre cable to expose the optical fibre.

22. A method according to claim 21, wherein the distal end of the optical fibre cable consists of the optical fibre.

23. An assembly substantially as herein described with reference to, and as illustrated by, FIGURES 1 to 7 or FIGURES 1 to 8 of the accompanying drawings.

24. A method of mounting an optical fibre cable to an optical device substantially as herein described with reference to, and as illustrated by, FIGURES 1 to 7 or FIGURES 1 to 8 of the accompanying drawings.