A differential quadrature phase shift key (DQPSK) optical modulator for use in a wavelength division multiplex (WDM) communication system

摘要

A modulator arrangement for modulating an optical signal using a differential quadrature phase shift key (DQPSK) for use in an optical wavelength division multiplex (WDM) communications system comprising a laser for producing an optical signal of a selected wavelength, which signal is split by a splitter 4, each part of said split signal being applied to a respective phase modulator 6, 8. The phase modulators are adapted to modulate the phase of the signal in dependence on a respective drive voltage and the phase of the output of at least one modulator is shiftable. The split signals are recombined by an optical recombiner 12 to form an optical phase shift key output. The arrangement further comprises a phase modulator 20 adapted to chirp the optical phase shift key output. The phase modulator may apply a pi/4 phase modulation to the output signal and it may be driven by an oscillator which is phase locked with the data streams U k , V k . The phase modulator may further comprise an electrode over a waveguide through which the optical output propagates. The system may be used with 10Gb/sec data streams.