GB2136592A - Method of fabricating a fibre optic coupler - Google Patents

Abstract

The method of fabricating a low loss fused biconical taper fiber optic coupler comprises the steps of twisting a plurality of optical fibers together; forming a biconical taper region in the twisted fibers; removing a section from the taper region; splicing the adjacent ends of the taper region together after removal of the section to provide a resultant coupling region; and tapering the resultant coupling region to achieve optimum coupling parameters. <IMAGE>

Description

SPECIFICATION A method of fabricating a low loss fused biconical taper fiber optic coupler This invention relates to fiber optic couplers, and especially to a method of fabricating a low loss fused biconical taper fiber (FBT) optic coupler.

The fabrication of such FBT couplers has been described in these articles: D.C. Johnson, B.S.

Kawasaki and K.O. Hill, "Low Loss Reflection Star Couplers for Optical Fiber Distribution Systems", Applied Physics Letters, Vol. 35 (7), pages 479 - 481, 1 October 1979; E.G. Rawson, A.B. Nafarrate, "Star Couplers Using Fused Biconically Tapered Multimode Fibres", Electronic Letters, Vol. 14, No. 9,27 April 1978; and E.G. Rawson, M.D. Bailey, "Bitaper Star Couplers with Up to 100 Fiber Channels", Electronic Letters, Vol 15, No.4,5 July 1979. In these articles the FBT couplers are made by grouping any number, N, of optical fibers over some length, L, and twisting and fusing them together with a heat source while simultaneously pulling them to form a biconical taper of N fibers. Both reflection and transmission star couplers can be made by this method.

Typically, couplers used in fiber optic systems need to have an even distribution of power among the output ports of the coupler. Such power distribution has not been shown for FBT star couplers with acceptable insertion losses using the conventional technique above described. This appears to be due to a preferential recoupling of light back into the excited fiber of the coupler. The excited fiber, also termed the throughput fiber, always has a higher power level than any of the tapoff fibers, and this difference between tapoff and throughput fibers depends on the number of fibres in the coupler. For couplers with more than eight fibres, the throughput fiber has significantly more power (usually greater than 50%) than any of the tapoff ports.

One approach to this problem of uneven excitation is described in the specification of our Patent Application No. 8228717, to which attention is directed.

An object of the present invention is to provide another method for fabricating a fused biconical taper fiber optic coupler having improved uniformity of coupling as compared with that of the prior methods of fabrication referred to above.

According to the present invention there is provided a method of fabricating a low loss biconical taper fiber optic coupler comprising the steps of: twisting a plurality of optical fibers together; forming a biconical taper region in said twisted plurality of fibers; removing a section from said region, and after removal of said section, splicing adjacent ends of said region together, to provide a resultant coupling region.

There follows a description of a method of fabricating a biconical raper fiber optic coupler embodying this invention in a preferred form. The description refers to the accompanying drawings, in which: Figures 1-4 illustrate various steps in the method of fabricating a low loss fused biconical taper fiber optic coupler in accordance with the principles of the present invention.

The basic method of fabricating a low loss fused biconical taper fiber optic coupler involves the twisting of a plurality of optical fibers together as illustrated in Figure 1, and then forming a biconical taper region in the twisted plurality of fibers by heating and pulling as illustrated in Figure 2. (In Figure 1 the separation of the fibers has been exaggerated). The next step is to remove a centre section of the taper region as illustrated in Figure 3, and then the adjacent ends of the remaining portions of the region are spliced together again, minus the centre section, as illustrated in Figure 4. Then, by heating and pulling a tapering of the spliced together region is performed to obtain the desired length and minimum taper diameter so as to provide the optimum coupling parameters.

The resulting coupler has improved uniformity over the straight fused biconical taper because a discontinuity at the splice of the optical fiber cores at the spliced joint as illustrated in Figure 4 allows for improved mixing of light in the fused biconical taper region of the coupler.

An advantage of the technique of the present invention over a simple scribe, break and splice of the fused biconical taper is that the inherent twisting of the fiber cores is taken advantage of by removing a section of length L from the fused biconical taper region and then matching the remaining ends of the region to provide the splice joint of Figure 4.

1. A method of fabricating a low loss biconical taper fiber optic coupler comprising the steps of: twisting a plurality of optical fibers together; forming a biconical taper region in said twisted plurality of fibers; removing a section from said region; and after removal of said section, splicing adjacent ends of said region together, to provide a resultant coupling region.

2. A method according to claim 1,furtherinclud- ing a step of tapering said resultant coupling region to achieve optimum coupling parameters.

3. A method according to claims 1 or 2, wherein said step of forming the biconical taper region includes the steps of heating said twisted plurality of fibers, and pulling said heated twisted plurality of fibers to provide said region.

4. A method according to claim 2 or 3, wherein said step of tapering includes the steps of heating said resultant coupling regions and pulling said heated resultant coupling region.

5. A method of fabricating a low loss biconical taper fiber optic coupler substantially as herein before described with reference for the accompanying drawings.

6. A low loss biconical taper fiber optic coupler fabricated by the method in any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A method of fabricating a low loss fused biconical taper fiber optic coupler This invention relates to fiber optic couplers, and especially to a method of fabricating a low loss fused biconical taper fiber (FBT) optic coupler. The fabrication of such FBT couplers has been described in these articles: D.C. Johnson, B.S. Kawasaki and K.O. Hill, "Low Loss Reflection Star Couplers for Optical Fiber Distribution Systems", Applied Physics Letters, Vol. 35 (7), pages 479 - 481, 1 October 1979; E.G. Rawson, A.B. Nafarrate, "Star Couplers Using Fused Biconically Tapered Multimode Fibres", Electronic Letters, Vol. 14, No. 9,27 April 1978; and E.G. Rawson, M.D. Bailey, "Bitaper Star Couplers with Up to 100 Fiber Channels", Electronic Letters, Vol 15, No.4,5 July 1979. In these articles the FBT couplers are made by grouping any number, N, of optical fibers over some length, L, and twisting and fusing them together with a heat source while simultaneously pulling them to form a biconical taper of N fibers. Both reflection and transmission star couplers can be made by this method. Typically, couplers used in fiber optic systems need to have an even distribution of power among the output ports of the coupler. Such power distribution has not been shown for FBT star couplers with acceptable insertion losses using the conventional technique above described. This appears to be due to a preferential recoupling of light back into the excited fiber of the coupler. The excited fiber, also termed the throughput fiber, always has a higher power level than any of the tapoff fibers, and this difference between tapoff and throughput fibers depends on the number of fibres in the coupler. For couplers with more than eight fibres, the throughput fiber has significantly more power (usually greater than 50%) than any of the tapoff ports. One approach to this problem of uneven excitation is described in the specification of our Patent Application No. 8228717, to which attention is directed. An object of the present invention is to provide another method for fabricating a fused biconical taper fiber optic coupler having improved uniformity of coupling as compared with that of the prior methods of fabrication referred to above. According to the present invention there is provided a method of fabricating a low loss biconical taper fiber optic coupler comprising the steps of: twisting a plurality of optical fibers together; forming a biconical taper region in said twisted plurality of fibers; removing a section from said region, and after removal of said section, splicing adjacent ends of said region together, to provide a resultant coupling region. There follows a description of a method of fabricating a biconical raper fiber optic coupler embodying this invention in a preferred form. The description refers to the accompanying drawings, in which: Figures 1-4 illustrate various steps in the method of fabricating a low loss fused biconical taper fiber optic coupler in accordance with the principles of the present invention. The basic method of fabricating a low loss fused biconical taper fiber optic coupler involves the twisting of a plurality of optical fibers together as illustrated in Figure 1, and then forming a biconical taper region in the twisted plurality of fibers by heating and pulling as illustrated in Figure 2. (In Figure 1 the separation of the fibers has been exaggerated). The next step is to remove a centre section of the taper region as illustrated in Figure 3, and then the adjacent ends of the remaining portions of the region are spliced together again, minus the centre section, as illustrated in Figure 4. Then, by heating and pulling a tapering of the spliced together region is performed to obtain the desired length and minimum taper diameter so as to provide the optimum coupling parameters. The resulting coupler has improved uniformity over the straight fused biconical taper because a discontinuity at the splice of the optical fiber cores at the spliced joint as illustrated in Figure 4 allows for improved mixing of light in the fused biconical taper region of the coupler. An advantage of the technique of the present invention over a simple scribe, break and splice of the fused biconical taper is that the inherent twisting of the fiber cores is taken advantage of by removing a section of length L from the fused biconical taper region and then matching the remaining ends of the region to provide the splice joint of Figure 4. CLAIMS

1. A method of fabricating a low loss biconical taper fiber optic coupler comprising the steps of: twisting a plurality of optical fibers together; forming a biconical taper region in said twisted plurality of fibers; removing a section from said region; and after removal of said section, splicing adjacent ends of said region together, to provide a resultant coupling region.

2. A method according to claim 1,furtherinclud- ing a step of tapering said resultant coupling region to achieve optimum coupling parameters.

3. A method according to claims 1 or 2, wherein said step of forming the biconical taper region includes the steps of heating said twisted plurality of fibers, and pulling said heated twisted plurality of fibers to provide said region.

4. A method according to claim 2 or 3, wherein said step of tapering includes the steps of heating said resultant coupling regions and pulling said heated resultant coupling region.

5. A method of fabricating a low loss biconical taper fiber optic coupler substantially as herein before described with reference for the accompanying drawings.

6. A low loss biconical taper fiber optic coupler fabricated by the method in any preceding claim.