Nortel Networks Corporation

Seb J Savory

Richard E Epworth

James E Whiteaway

Robin Paul Rickard

A coherent receiver receives a set of signals which are spaced in phase, or phase and polarization, and a reference signal. The receiver processes the set of signals to determine which of the set of signals has a predetermined association (e.g. closest in phase) with the reference signal and selects that signal as an optimum output. The receiver has the effect of de-rotating the phase slip between the input signal and reference signal in discrete steps. The selecting occurs on a repeated basis to select an optimum output. The set of signals can be processed in the analogue or digital domains, by such techniques as: comparing the amplitude of each of the set of signals with a threshold, comparing signals with each other or cross-correlation. The processing can be implemented, if desired, without the need for complicated components, which would either be expensive or become unreliable at the extreme high operating frequencies used for optical communication.

Coherent receiver

A receiver for an optical transmission system, has a polarization diverse and phase diverse coherent optical receiver, and a digital adaptive equalizer for compensating for distortions in the optical signal introduced by the optical path. The entire field of the optical signal is mapped including phase and polarization information, to enable more complete compensation for impairments such as chromatic dispersion and PMD. Furthermore, it can also reduce the problems which have so far held back coherent optical detection from widespread implementation, such as polarization alignment and phase tracking. This can be applied to upgrade existing installed transmission routes to increase capacity without the expense of replacing the old fiber.

Digital compensation for optical transmission system

A coherent optical intradyne receiver is described which comprises an optical image reject mixer capable of dividing, mixing and recombining signals from three inputs so as to produce an inphase and a quadrature channel. On each of the channels a same set of image products is cancelled and from which channels, phase modulated signals can be recovered.

Coherent optical receiver

An optical couplercomprising at least three fibresand, portions of the fibres being fused to each other to form a coupling regionoperable to couple light therebetween. At least two of the fibres have inputsand/orand/orand at least two of the fibres have outputsand/orand/or. In use, on illumination of at least two of the inputs light intensity is emitted from a plurality of the outputs having a substantially asymmetric phase relationship, such as, for example, a quadrature phase relationship between two of the outputs. The invention also provides for methods of making such a device.

3 Fibre I and Q coupler

A PMD compensator has three compensation elements in series, each for providing variable differential group delay. Each compensation element provides compensation along a different orthogonal polarization axis. This enables PMD to be cancelled more completely.

Growing community of inventors

Cambridge, United Kingdom

Seb J Savory