Optical modulation device

DETAILED DESCRIPTION The present invention provides an optical modulation device comprising an optical modulator for modulating an incoming light beam in accordance with an input modulation signal, an optical detector for producing, from a modulated optical output from the optical modulator, an intensity-of-light signal proportional to an intensity of the modulated optical output, a first and a second duty ratio detector for detecting duty ratios of the input modulation signal and the intensity-of-light signal from the optical detector, respectively, a differential amplifier for producing a difference signal between outputs from the first and second duty ratio detectors, and a bias amplifier for applying the difference signal from the differential amplifier to the optical modulator.
Preferably each of the first and second duty ratio detectors may include a voltage comparator for comparing an input signal with a reference signal to deliver a binary voltage signal and a low-pass filter connected to the voltage comparator.
Alternatively, each of the first and second duty ratio detectors may include a positive inversion circuit for delivering an input signal as intact and a signal inverted therefrom, a pair of low-pass filters having the input signal and the inverted signal applied thereto from the positive inversion circuit respectively, and a differential amplifier having applied thereto outputs from the pair of low-pass filters.