NZ235139A

NZ235139A - Forming fused-fibre optical coupler

Info

Publication number: NZ235139A
Application number: NZ23513990A
Authority: NZ
Inventors: Rolf Rossberg; Friedemann Mohr
Original assignee: Alcatel Australia
Priority date: 1990-08-31
Filing date: 1990-08-31
Publication date: 1993-02-25

Description

<div class="application article clearfix" id="description"> A 235 139 Priority Datejs): ..1'.?,^ ) Complete C "&V Class- PP"^<a>2r\ W- Co2.o>io\-2-is ) Publication O-?' :-: P.O. J.r.i.r,• . llsfe?. 25 FEB 1993 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "OPTICAL COUPLER" , £ ft A* °\ ;:3 I AUG 19907/ ;WE, gTANDARD TELEPHONED AND CADLES PTY. LIMITED, A Company of the State of New South Wales, of 252-280 Botany Road, Alexandria, New South Wales, 2015, Australia, hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: ;1 ;235139 ;This invention is based on a fused-fibre coupler. ;Prom POT Application WO 84/04822, a fused-fibre optical coupler is known which consists of two single-mode fibres welded together in parallel along a length in the centimeter 5 range and drawn to thereby form a coupler. The coupling re gion and the associated stripped fibres are placed in a housing. The fibre ends of the coupler are then spliced to a fibre of the communication line or to another electro-optic converter, for which reason the free ends of the cou-10 pier must be relatively long. ;If such a coupler made of single-mode fibres is spliced to polarization-mnaintaining fibres, one of the optical axes must lie in the coupling plane (and the other must be perpendicular to the coupling plane), so that the degree of 15 polarization (extinction) of the polarized light is re tained. For this, the coupler fibres must be as short as possible to prevent depolarization of the light. This is very difficult to accomplish with the known coupler. ;It is desirable to produce a coupler from single-mode 20 fibres which coupler can be manufactured cost-effectively and can be used in particular in connection with polarization-maintaining fibres. ;This specification describes a method of manufacturing a fused-fibre coupler from nonbirefringent single-mode 25 fibres which serves to interconnect optical fibres, the method including the following steps: splicing a short length of nonbirefringent single-mode fibre between the op- ;2 ;*35139 tical fibres; fusing the spliced-in single-mode fibres together and drawing them to form a coupler, and embedding the coupler in a housing up to points beyond the splices in a stress-free manner. In particular, the advantages obtained with the manufacturing method according to the invention are that the single-mode fibres forming the coupler are very short, that the splicing of the polarization-maintaining optical fibres can be performed without difficulty in spite of the short length of the single-mode fibres, that—in the case of polarization-maintaining optical fibres—before splicing of the single-mode fibres, the optical axes of the polarization-maintaining optical fibres can be aligned with each other in the coupling plane, and that the coupler is embedded in a housing up to points beyond the spliced polarization-maintaining fibres in a stress-free manner and protected against environmental effects. Using one example, the method for manufacturing a coupler according to the invention is explained in detail in connection with the drawings. Pig. 1 shows two polarization-maintaining optical fibres, separated in the middle, lying parallel to each other, schematically; Pig. 2 shows the two polarization-maintaining fibres from Pig. 1, into each of which respectively is spliced a short piece of a single-mode fibre, schematically; 235 1 39 Pig. 3 shows the arrangement of the fibres from Pig. 2, at the time of fusion to form the coupler, schematically; Pig. 4 shows the arrangement of the single-mode fibres from Pig. 3 after being fused and pulled to form a coupler, schematically. Pigs. 1 through 4 show, schematically, four stages in the course of the manufacturing process of a coupler according to the invention. For the sake of clarity, representation of the usual protective coating of the actual waveguide, the waveguide being hereinafter referred to as the "fibre" is omitted. The stripping of the fibres, their preliminary handling, and the fusing into a coupler is sufficiently known and is also described in detail in the PCT application WO 84/04822 mentioned above. Pig. 1 shows two parallel fibres which have been separated in the middle to permit insertion of a short piece of a single-mode fibre and which form the optical fibres 1 and 2. When the fibres are polarization-maintaining fibres, i.e., fibres which are linearly birefringent in the lengthwise direction, before the single-mode fibres are spliced in, the optical axes of the optical fibres 1 and 2 must be aligned with each other pairwise in the plane of the coupler (6) to be formed (Fig. 4) in such a way that in each case one of the two optical axes of the fibres lies in the coupling plane. The optical fibres 1 and 2 are fixed in this position. When the optical fibres 1 and 2 are not 2351J9 birefringent, I.e. not polarization-maintaining fibres, such alignment is not necessary. In this case, the optical fibres 1 and 2 are only fixed in position for splicing. The ends of the optical fibres 1 and 2 positioned in this manner are then separated far enough from each other that In each case an approximately 1 to 2 centimeter long piece of a single-mode fibre 3 or 4 can be spliced in between the optical fibres 1 or 2. This stage is shown In Pig. 2. Then, the two single-mode fibres 3 and 4 In the spliced condition are fused to each other In known fashion (Pig. 3) and pulled to form a coupler 6 (Pig. 4). Care Is taken during this process to assure that the orientation of the optical fibres 1 and 2 to each other and to the coupling plane does not change. The coupler 6 is then embedded in a stress-free manner and protected against environmental effects up to points beyond the splices 5 in a housing 7 represented here only by Its outline. Fused-fibre couplers can be made from various types of polarization-maintaining fibres, provided that one uses only fibres that do not have any increases In the refractive index outside the core area. For low-loss couplers, fibres are preferred in which the stress-applying parts parallel to the fibre core which cause the birefringence are matched to the refractive index of the cladding glass. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 23 5 1 3! What we claim is:

1. A method of manufacturing a fused-fibre coupler from nonbirefringent single-mode fibres which serves to interconnect optical fibres, the method including the following steps: splicing a short length of nonbirefringent single-mode fibre between the optical fibres; fusing the spliced-in single-mode fibres together and drawing them to form a coupler, and embedding the coupler in a housing up to points beyond the splices in a stress-free manner.

2. A method as claimed in claim 1, wherein said optical fibres to be interconnected are polarization-maintaining optical fibres, said method including, prior to the step of splicing a short length of non-birefringent single-mode fibre between the optical fibres, the steps of aligning the optical axes of the optical fibres, with one of the two optical axes lying in the plane of the coupler to be framed, and fixing the optical fibres in position.

3. A method as claimed in claim 2, wherein said short length of nonbirefringent single-mode fibre spliced between the optical fibres is a birefringent polarization-maintaining single-mode fibre.

4. A method of manufacturing a fused-fibre coupler as herein described with reference to the accompanying drawings.

5. A fused-fibre coupler manufactured by a method as claimed in any one of claims 1 to 4 wherein the single-mode fibres forming the coupler proper have a length of from 1 to 2 cm.

6. A fused-fibre coupler as herein described with reference to the accompanying drawings. ALCATEL AUSTRALIA LIMITED flfy >v 4 v B. O'Connor - Authorized Agent P5/1/1703 2 1 ^ ^ </div>