Northern Telecom Limited

Nortel Networks Corporation

Stc, Inc

Standard Telephones & Cables Public Ltd. Co.

Alan Fielding

Terry Bricheno

James E Whiteaway

Stephen Day

Sandra Davis

George H Thompson

Kevin C Byron

Terry Victor Clapp

Michael F Grant

Robert A Baker

Vernon Baker

Christopher Chew

Nicholas A Hewish

Nicholas J Pitt

Arrayed waveguide grating

It is found that the use of a multimode interference (MMI) section to flatten the pass-bands of an arrayed waveguide grating (AWG) multiplexer/demultiplexer or comb filter device introduces undesirable wavelength dispersion into those pass-bands if that MMI section mixes modes of more than two different orders, and if the grating of that device is a 'uniform' grating whose waveguides are equally (minimally) attenuating, and in which the optical path length difference between each adjacent pair of waveguides of the array is the same. This dispersion can be substantially compensated by appropriate 'tailoring' of the grating to remove such uniformity

Optical arrayed waveguide grating devices

It is found that the use of a multimode interference (MMI) section to flatten the pass-bands of an arrayed waveguide grating (AWG) multiplexer/demultiplexer or comb filter introduces undesirable non-linear wavelength dispersion into those pass-bands if that MMI section mixes modes of more than two different orders. This dispersion can be substantially compensated by the use of a tandem arrangement of two AWGs with MMIs of differing length chosen to provide complementary dispersions. In the case of a comb filter, an equivalent compensation can be achieved by arranging for the light to make a second passage through the AWG in the reverse direction.

A channel insertion filter for a WDM system is provided by an optical waveguide Mach Zehnder comprising a pair of 3dB couplers interconnected by a pair of interference arms in which are created a pair of Bragg reflectors. These reflectors are partially reflecting at the channel insertion wavelength so that some of the light of the associated channel transmitter is transmitted by them to provide a feedback control loop error signal for regulating the emission wavelength of the transmitter.

WDM channel insertion

Optical fiber elements, such as narrow pass-band filters, dispersion equalizers, and channel dropping filters, are constructed from 2.times.2 single mode optical fiber fused tapered couplers having formed on one side of coupling regions Bragg distributed gratings in the two fibers from which the coupler is constructed. By making the gratings at a point where the fibers remain fused together in side-by-side contact it is ensured that they lie equidistant from the coupling region.

Optical fibre Bragg distributed gratings

An optical fibre amplifier in which a length of optically amplifying fibre is spliced between a pair of 2.times.2 tapered fused fibre couplers each constructed from a length of amplifier type profile fibre and a length of transmission type profile fibre. In each coupler, one of two constituent fibres has been pre-stretched so as to match the propagation constants of the two fibres within the coupling region of that coupler.

Optical fibre amplifier

A wavelength multiplexing tapered fused fibre coupler is used to splice a second length of optical amplifier fibre between first and third lengths in such a way that pump power bypasses it. The second length is therefore unpumped and acts as a notch filter smoothing out the spectral gain characteristic of the first and third lengths.

Optical waveguide gain-shaped amplifier including wavelength

In the manufacture of a wavelength multiplexing 2.times.2 tapered fused fiber coupler by progressive stretching, the birefringence of the coupler resulting from the progressive stretching is subsequently nulled-out by elastic twisting of the coupler. The progressive stretching is performed, under temperature conditions providing a profile in the coupling region of the coupler having the property that the coupling strength for one of the principal polarization planes of the coupler remains substantially constant during said elastic twisting.

Polarization insensitive wavelength multiplexing 2.times.2 fibre couplers

A 1.times.N single mode optical waveguide coupler comprises a single input optical fibre (1), a slab-like mixer waveguide (3) and a plurality (N) of output optical fibres (2). As a result of interference effects light introduced into the mixer waveguide (3) via the centrally located input fibre (1) produces a linear array of output spots at various intervals along the length of the mixer waveguide. The length of the mixer waveguide is chosen such that the output optical fibres are aligned with one such array of output spots. The fibres may be adiabatically tapered to a smaller diameter in order to increase their modal spot size.

Single mode couplers

An active optical fibre star coupler having a length of amplifying optical fibre (1) optically connected at one end to a wavelength combining coupler (2) and at the other end to via a beam expanding element (3) to a set of output optical fibres.

Active optical fibre star coupler

A method of making a single mode optical fibre directional coupler in which a pair of fibres (30,31) in side-by-side contact is subjected to a succession of drawing operations produced by traversing the fibres longitudinally through a flame (34) while stretching them between a pair of carriages (32,33) driven at slightly different speeds.

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Bishops Stortford, United Kingdom

Alan Fielding