GB2389916A

GB2389916A - Fine alignment of optic fibres to optical components

Info

Publication number: GB2389916A
Application number: GB0214274A
Authority: GB
Inventors: Christophe Philippe Prel
Original assignee: Bookham Technology PLC
Current assignee: Lumentum Technology UK Ltd
Priority date: 2002-06-20
Filing date: 2002-06-20
Publication date: 2003-12-24
Also published as: GB0214274D0

Abstract

Optic fibres 19 which may extend from fibre ribbon 21 are coupled to an array of optical components 16, by using a holding structure such as U-grooves 14 in a pre-alignment configuration with respect to the array of optical components 16. The holding structure 14 allows lateral adjustment of the ends of the fibres with respect to each other and the optical components such as by manipulation or waggling of the fibre ribbon 21 so as to achieve a relatively fine optical alignment of the fibres 19 with the optical components 16. The optic fibres 19 can then be secured by using a UV light curable epoxy adhesive with the array of optical components 16. Tapered U-grooves with a pinch point at the end closest to waveguides 16 may be used to avoid having the fibre stick to the sides of the U-groove during manipulation.

Description

238991 6

OPTIC L'I13REL.-\l,IClNSlENT The present invention relates to a method and device for coupling an array of optic fibres to an arra,' of optical components. -en embodiment of the invention relates to a method and device for coupling an array of optic fibres with an array of waTeguides defined in an optic chip.

()ptical fibre communication systems, in particular, multi-channel systems, often rccluire the coupling of an array of optic fibres with integrated optical devices such as a demultiplexer/multiplexer via an array of vaveguides defined in an optic chip.

l'lMis is currently typically carried out by joining a fibre block, which securely holds the ends of the optic fibres at a polished leading face thereof in a fixed configuration, to an angled polished chip edge at which the waTeguides terminate.

It has been absented that there are several problems with this method in obtaining good alignment between the optic fibres and the waveguides. First, there is a problem of bulk misalignment wherein, the fibrcs 4 are not supported in a completely planar configuration resulting from variations in the dimensions (depth) of the grooves provided on the fibrc blocl; to receive and hold the optic fibres, or from roughness or warping of the fibre block components in a concave (a) or convex (b) fashion (see Figure 1, in which c>nl!t one half of the fibre block is she awn). i! compromise alignment has been achieved by optimising the light path fair to end timbres 4a, 4b, or possibly two cod fibres 4a, 4b and a middle Able 4c.

XY'ith such a method some of the fibres may inevitably be poorly aligned with their respective waveguides. Secondly, in each individual fibre 4 the core ( of the fibre may not be consistently centred in the middle of the fibre but rather randomly displaced off-centre as a result of the manufacturing process, as shown in Figure 2 (in which only one half of the fibre block is shown). 1Nccordinglv, even if a very Fact geometric or bulk alignment of the fibrcs is achieved with the fibre block, Optimal optical alignment with the waveguides ma! not be possible due to off-

ccntre cores.

It is an aim of the present invention to provide an alternative technique for coupling a plurality of,ptic fibres to a plurality of septic components with which these problems may be at least partially solved.

\cccrding to a first aspect of the present invention there is provided a method of coupling a plurality of longitudinal optic fibres to an array of optical components including the steps,f: locating the plurality,f optic fibres in a holding structure in a prc-alignment configuration with respect to the array of optical components the holding structure allowing lateral adjustment of the ends of the fibrcs with respect t, each other and the optical components; adjusting the configuration,f the optic fibres within the holding structure so as to achieve a relatively fine optical alignment of the fibres with the optical components; and securing the optic fibres in relatively fine cryptical alignment with the array of optical components.

\ccording to a second aspect of the present invention there is pros ided a method >f coupling an array 'f optic fibrcs extending from a fibre ribbon try an array of optical waveguides defined in an optic chip; the method including the steps of: (a) locating the plurality of optic fibres in an array 'f longitudinal holding grooves I defined in the optic chip in a pre-alignment configuration with respect to the array ,f waveguides the holding grooves allowing lateral adjustment of the ends of the optic fibres with respect to the optical waveguides; (b) manipulating the fibre ribbon to bring fine of the optic fibres into relatively fine optical alignment with the respective one of the array of wavcguides; (c) securing said one optic fibre in relatively fine alignment with the respective one of the array of waveguides; and I repeating steps (l,) and (c) for each Able so as tr, individually align and secure each fibre with respect to the respective waveguide.

According t, a third aspect of the present invention there is provided an optic device including an optic chip defining an array,f optical components; and an array of holding grooves for loosely holding an array of optic fibres in a pre-

alignment configuration with respect to the optical components the grooves

designed to allow fine lateral adjustment of the ends of the optic hbres with respect to each ot.hcr and the optical components.

I'mbcdiments cJf the present invention will now be described, by \vey of example À,nlv, with reference to the accompanying drawings in which: Figure 1 illustrates the problem of bulk misalignment in a conventional technique; F igure 2 illustrates the problem of off-centrc cores in a conventional technique; l;igure 3 shows an embodiment of the present ins ention with a plurality of fibres aligned in a plurality of U-grooves with an array of wareguides; I;igurc 4 illustrates in perspective e the relative position of the U-groove and wa,Teguide in an embodiment of the present insTenticn; I;igure 5 shows another embodiment of the present invention using a plurality of tapered U-groovcs; I leisure 6 shows the geometry of an end portion of the wa-eguide in an embodiment of the present invention; and I;igure 7 shows an example of the geometric arrangement of the end of a fibre and the end of the rcspectix c waveguide. I Referring first to Figure 3, an optical device according to a first embodiment of the present invention includes an optic chip 2 defining an array of rib waveguides 16 terminating at a clrv-etched facet 17 and a plurality' of U-grooves 14 for loosely holding an array of stripped optic fibres 19 extending from a fibre ribbon 21 in alignment with the end of the ends of the wave,guides.;

lithe optic chip further defines a glue relief slot 2() between the Ugrooves 14 and the dry etched facet 17 to receive any excess adhesive used, as described later, for securing the fibrcs in the U-grooves. The optic chip also defines a ribbon cladding tic-,ff pocket 22 at the other end of the plurality of U-grooves 14 for receiving an cod portion of the fibre ribbon. 'lthe pocket 22 extends to the edge of the optic chip. 'l'he U-gr'o'es, glue relief slot and ribbon cladding tie-off pocket are all formed by dry etching of the optic chip.

l'he U-grooves are designed to provide suitable free-play to manipulate the hbres 1) within the U-grooves 14 to obtain a fine lateral alignment of the laser cleaved cads 25 of the 'ptic fibres with the waveguidcs 1(, prior to fixing. In a method according to an embodiment of the present invention, an array of stripped optic fibres 19 extending from a fibre ribbon 21 have their ends 25 laser-cleaved at an angle and arc located in the U-grooves 14, which loosely hold the fibres 19 so as to be roughly aligned with the ends of the svaveguides 16. Uncured epoxy adhesive is provided in the U-grooves 14 and is used at a later step to secure the fibres in the U-grooves 14. A first one of the fibres 19 is then fineyv aligned with the end of the respective waveguide 1G in an active alignment process by mechanically manipulating ("waggling") the fibrc ribbon 21. Once the optical alignment of this hrst optic fibre is optimised, it is secured by selectively curing the epoxy adhesirc in the respective U-groovc 14. 'lithe epoxy adhesive may, for example, be curable using UV light. This process is repeated in succession for each of the optic hbrcs 19. Manipulation (vaggling) of the fibrc ribbon f'r aligning subsequcot fibrcs does not affect the alignment of the previous Libras as these have Ready been secured in the aligned position and as the individual timbres in the U-grooves come into fine alignment with the waveguidc tines are fixed.

Manipulation of the fibre ribbon rather than the individual optic fibres themselves is particularly advantageous where the fibres arc small and bustle. ()nc approach is to have an initial large amplitude movement of the ribbon fibre, and then to gradually reduce the amplitude calf the movement to gain a finer and fiecr alignment prior tO fixing. The fine alignment step may be automated.

Ill one embodiment, the active alignment step is carried out as folk,\vs. A known intensity of light is passed through the respective fibre, and the intcnsin' of light output from the waveguide is measured as the fibres are manipulated. When a hbrc comes into "best" alignment such that a maximum intensity of output light is detected UV light is automatically and selectix ely directed at the U-groovc containing the fibre to cure the epoxy and thus fix the fibre in the aligned position. preferably this manipulation of the fibre, monitoring of the output light, and curing of the epoxy adhesive is carried out in an integrated and automatic process. Such a process provides a quick and accurate method of reobtaining a high performance optical connection with an epoxy free optical path.

An example of the dimensions and geometry' for the illustrated embodiment of [iigutc 3 are as follows: I i-groove width (a) 1 45m U-groove length (b) I()()O'lm [l-groove depth X()m (flue relief slot length (d) 5()01lm (, lue relief slot depth 1 7OIlm al ic-off length (f) 2()00,um l de-off depth Mom liacet type perpendicular with angled slots Waveguide type 1 () pm inclined at 5' to the facet I nterface type Free-air I hose dimensions are selected to provide suitable free-play for manipulation and alignment of the individual fibres, and also to provide a strong reliable bond after fixing without using an excessive area of the chip. [or example, if the depths of the glue relief slot and the tie-off are reduced and the length of the glue relief slot is inctcased, problems may be encountered in manipulating the fibres remotely due to the excessive length of the Ugrooves (and the stripped portions of the s

flares). Also, once attached, a longer glue relief slot may allow c,; ccssive fibre moTemcnt over time.

lthc stripped fibre length in the design shown in I;igure 5 is only 2()() ()llm, which dimension has been selected with a view to providing a stiff fibrc assembly, and avoiding fibre "droop" in front of the wavegulde. '['his design is selected with a v few to rriinimising the degree of manipulation of the ribbon fibre necessary to find the minimum loss for each fibrc-waveguide connection.

In the present embodiment, the end of the waveguide is provided with an anti-

reflection nitride coating and the interface 23 between the laser cleaved fibre end and the svaveguidc is free-air coupled. However, a gel coupled interface may also be used.

Figure 5 shows an alternative embodiment of the present invention with tapered U-groovcs to girc a pinch point at the end cksest to the waveguides. The dimensions of the U-grocves arc as follows: U-grorve end widths (k, l) 145, 190pm Alternative U-groove end widths (m, n) 1.(), 190ilm It has been found the use of tapered U-gtooves helps avoid the fibre sticking slightly to the sides of the U-grooYe when moving the fibre during the fine alignment manipulation step.

Figure 7 illustrates an example of the optic fibre laser cleave angles and waveguide facet angles. The optic fibre in the illustrated embodiment lies in the same plane as the waveguide. 'lthe waveguide is arranged at an angle of 7 degrees relative to the direction of light from the fbrc so as to minimisc back reflection. Furthermore, the facet is set at an angle of 12 degrees from perpendicular to the direction of light from the fibre and parallel with an end face of the laser cleaved fibre end 25 so as to minimise back reflection.

Vertical tapering technology of the kind described in WO01/27G7() may be used to improve the coupling of the fibres and the waveguides. An example of the comctry for the end portion of each waveguide is shown in [Figure 6. Starting from the end at the dry etched facet, the waveguide includes a 3()()m long straight section ',() of relatively large uniform width and height, a tapered section 9 including an upper portion 34 of decreasing width away from the edge facet and a 1o\ver portion 3(, which tapers down to a width of 41lm, a tapered section 38 <,f ().1, half angle leading to a 4rnrn long mode filter section 40, additional padding section 42 to make the total length up to Xmm, and a tapered section 44 increasing in width to 61lm at 0.1, half angle.

l'he above-descriEcd techniques provide for fibrc attach in which no angled fibrc block or polishing of the chip is required, and allow fine optical alignment resulting in a high performance coupling power (low coupling loss after fibre attach). These techniques arc compatible with, for example, both 1(),um and 51lm core fibres.

l'he applicant draws attention to the fact that the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any gencralisation thereof, without limitation to the scope of any definitions set out above. In view of the foregoing description it will be evident to

a person skilled in the art that various modifications may be made within the sc,pc of the imrcation.

Claims

(,I,.\INItS: 1. A metho:l of coupling a plurality of longitudinal optic

fibres t, an array of optical components, including the steps of: kcating the plurality of optic fibres in a holding structure in a pre-alignment configuration with respect to the array of ,ptical components, the holding structure allowing lateral adjustment calf the ends <,f the fibres with respect to each other and the optical components; adjusting the configuration of the optic fibres within the holding structure so as to achieve a rclatirely fine optical alignment of the fibres with the optical components; and securing the optic timbres in relatively fine optical alignment with the array of Cortical components.

9. A method according to claim 1, wherein each of the plurality off fibres is placed between a respective pair of opposed constraining surfaces to, pre-align each fire with the respective optical component, the opposed surfaces distanced b! an amount larger than the diameter of the fibres.

3. method according to claim 1 or claim 2, wherein the optic fibres extend from a fibre ribbon and the configuration of the optic fibres is adjusted within the holding structure by manipulating the fibre ribbon.

4.,\ method according to any preceding claim, wherein each optic Abbe is individually aligned and secured.

:. -\ method according to any preceding claim, wherein the holding structure and the array of optical components are integrated together in an optic chip.

(. A method according to claim 5, wherein the optic fibres extend from a fire ribbon and including the step of knotting an end portion of the fibre ribbon on rhc optic chip.

7. if method according to claim 5, wherein the holding structure comprises a plurality of longitudinal grooves defined by the optic chip.

S. A method according to claim 7 wherein the optic fibres are secured in the gr,ores by adhesion e.

i)..N method according to claim 8 wherein an adhesive relief skit is provided lcveen the grooN es and the optical components to avoid excess adhesive becoming adhered to the optical components.

1). A method according to claim 7 wherein the grooves are tapered inwardly in the longitudinal direction towards the optical components.

11. A method of coupling an array of optic fibres extending from a fibre nbbc>n to an array of optical waveguides defined in an optic chip; the method including the steps of: (a) locating the plurality off optic fibres in an array of longitudinal holding grooves defined in the cryptic chip in a pre-alignmeat ccnfuraticn faith respect to the array of oval eguides, the holding grooves allowing lateral adjustment of the ends of the optic fibres with respect to the ,ptical waveguides; (b) manipulating the fibre ribbon to bring one calf the optic filJres into relatively fine optical alignment with the respective one of the array of vaveguides; (e) securing said one optic fibre in relatively fine alignment with the respective one of the array of waveguides; and repeating steps (1) and (c) for each flare so as to indi\riduallv align and secure each fibre with respect to the respective wa-eguide. 1. An optic de\'iee including an optic chip defining an array of optical components; and an array of holding grooves for loosely holding an array of optic fibres in a pre- alignment configuration with respect to the optical components, the grooves designed to allow fine lateral adjustment of the ends of the optic fibres with respect to each other and the optical components.

1.. An optic device according to Cow 12, wherein the optic chip defines an adhesive relief slot between the grooves and the optical components for preventing adhesive used to secure optic fibres in the grooves from adhering to the optical components.

14. An optic device according to claim 12 or claim 13, wherein the optic chip dt fines structure for locating a hbre ribbon from which the optic hbrcs cstend.

15. An optic device according to any of claims 12 to 14, wherein the grooves i arc tapered inwardly in the longitudinal direction towards the optical components.

1(,. An optic system including an optic device according to any elf claims 12 to 15, and an array Off optic fibres secured by adhesive in the holding grooves, the I adhesive serving to also fix the configuration of the fibres within the holding grooves. 17. A method, optic device or optic system substantially as hcrcinbefore described with reference to any of the accompanying drawings.