# US 5,703,976 A · Wavelength resonant fused fibre coupler

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- Number: US 5,703,976 A
- Document ID: US5703976A
- Status: Granted
- Kind: A
- Application number: 08/557,857
- Filed: 1995-11-14
- Granted: 1997-12-30
- Earliest claimed: 1994-11-15
- Assignees: Northern Telecom Limited
- Inventors: Thomas John Cullen
- Web page: https://patentgrep.com/patent/US5703976A

## CPC

- G02B 6/29332: {Wavelength selective couplers, i.e. based on evanescent coupling between light guides, e.g. fused fibre couplers with transverse coupling between fibres having different propagation constant wavelength dependency}
- G02B 6/2552: {reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A wavelength selective 2.times.2 single mode fibre coupler has a weakly coupled coupling region n which the cladding modes of the two fibres are coupled while the core modes remain uncoupled. A matched pair of core/cladding mode converters are located, one on one fibre on one side of the coupling region, and the other on the other fibre on the other side.

## Claims

### Claim 1

A wavelength selective fibre coupler having first and second single mode optical fibres each capable of supporting a core mode and a cladding mode, which coupler is provided with a coupling region through which the core mode of each fibre propagates in a manner effectively uncoupled with the core mode of the other fibre, and in which coupling region the cladding modes of the fibres are optically coupled, which coupler additionally includes a matched pair of spectrally selective resonant core/cladding mode converters provided respectively on the first and second optical fibres respectively upstream and downstream of the coupling region.

### Claim 2 (depends on 1)

A coupler as claimed in claim 1, wherein the members of the matched pair of mode converters are distinguished in that for only one of the mode converters is the coupling efficiency maximised.

### Claim 3 (depends on 1)

A coupler as claimed in claim 1, wherein the coupling efficiency of both mode converters is maximised.

### Claim 4 (depends on 1)

A coupler as claimed in claim 1, wherein the coupling region is a tapered fused fibre type coupling region.

### Claim 5 (depends on 1)

A coupler as claimed in claim 1, wherein the coupling region is a polished half-coupler type coupling region.

### Claim 6 (depends on 1)

A coupler as claimed in claim 1, wherein each of the mode converters provides the fibre of that mode converter with a periodic structure composed of two or more sections of different periodicity.

### Claim 7 (depends on 1)

A coupler as claimed in claim 1, wherein each of the mode converters provides the fibre of that mode converter with a periodic structure the periodicity of which is chirped.

### Claim 8 (depends on 1)

A coupler as claimed in claim 1, wherein each of the mode converters has a periodic structure induced by the urging of the fibre of that mode converter against a ribbed surface.

### Claim 9 (depends on 1)

A coupler as claimed in claim 1, wherein each of the mode converters has a periodic structure consisting of a set of axially spaced perturbations in the fibre of the converter, each of which perturbations has been created by axially stretching the fibre to produce plastic deformation in a heat-softened zone thereof sufficiently sharply localised to result in the formation of a non-adiabatic taper.

### Claim 10 (depends on 1)

A plurality of couplers as claimed in claim 1, the members of which plurality are connected optically in cascade.

### Claim 11 (depends on 1)

A method of operating an optical transmission system which method of operation includes transmission of optical signals from a transmitter to a receiver through one or more wavelength selective fibre couplers as claimed in claim 1.