Northern Telecom Limited

British Telecommunications Public Limited Company

Ceorl Limited

John E Carroll

Ian H White

Richard S Linton

Mark C Nowell

Barry John Flanigan

Adrian R Travis

A DFB laser is provided with a top electrode divided symmetrically into two or three in-line separate elements through which a bias current is applied with a symmetrical distribution and through which a modulation current is applied in push-pull with a temporal asymmetry.

Direct amplitude modulation of lasers

A coherent detector which is insensitive to signal or polarization state may be assembled using a fused optical fibre multiport constructed from five optical fibres. The fibres are fused in a circularly symmetric arrangement, then tapered until power injected into any input is equally distributed to all outputs. Reference signals are injected into adjacent inputs and the signal to be detected into a signal adjacent one of the reference inputs.

Optical fiber multiport apparatus for detecting phase shifts

A DFB laser is provided with a top electrode divided symmetrically into two or three in-line separate elements through which a bias current is applied with a symmetrical distribution and through which a modulation current is applied with an antisymmetric (push-pull) distribution.

An opto-electronic switch which shows a good signal rejection ratio between modes is also of particularly small dimensions. The switch comprises a semiconductor laser 1 having four contacts 12, 12', 13, 13' which provide gain guiding under two stripe windows 18, 19. By varying the bias currents supplied to the individual contacts 12, 12', 13, 13', or inputting optical control signals to the waveguiding channels under the stripe windows 18, 19, different configurations of optical output from the laser 1 can be achieved. The two contacts, 12, 12' and 13, 13', associated with each stripe window 18, 19 are effectively a signal stripe contact with a discontinuity. It is thought that diffractive transverse coupling at the discontinuity allows the use of a shorter device than in known directional switches. With feedback, the switch operates as a memory device. The switch finds particular application in optical communications, for instance in signal routing.

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Cambridge, United Kingdom

John E Carroll