AUTOMATIC BIAS CONTROL FOR AN OPTICAL MODULATOR

摘要

An automatic bias controller for an optical modulator (18) is provided. The automatic bias controller comprises a driver (25) for providing an electrical data signal to the modulator and bias means for providing a bias voltage to the modulator. A microprocessor (74) provides a low frequency digital modulation signal, which is converted to an analogue modulation signal by a digital to analogue converter (76). The analogue modulation signal is applied to the bias means (so as to modulate the bias voltage) or to the driver (so as to modulate the amplitude of the data signal). Intensity detection means (70) for detecting the intensity of light emitted by the modulator are provided, and an analogue to digital converter (72) converts the output of the intensity detection means to a digital intensity signal which is passed to the microprocessor. The digital intensity signal is analysed, and the bias means instructed to adjust the bias voltage on the basis of the analysed signal. The digital modulation signal is preferably a rectangular wave or time multiplexed series of periods in which the bias voltage and data signal amplitude are varied.