Electro-optic gating arrangement with improved duty cycle

An electro-optical gating device for generating a pulse stream with adjustable pulse width for use in an optical communication system using a return-to-zero signaling format, the device comprising oscillator means to generate a substantially sinusoidal input electrical signal of a pre-determined frequency fLO, means to split said input electrical signal into first and second signals, variable amplifier or attenuator means adapted to allow adjustment of an amplitude of said second signal relative to an amplitude of said first signal, means to triple the frequency of said second signal to 3fLO, means to recombine said tripled second signal with said first signal to produce a combined electrical signal, and a Mach-Zehnder modulator with a substantially sinusoidal response curve and arranged to be biased for maximum optical transmission adapted to be driven by said combined electrical signal to produce an optical pulse train at twice the frequency of the input electrical signal with an adjustable duty cycle.