Patent ID: 7555226
Filing Date: 2009-06-30
Classification: G02F,H04B

Abstract:
1. An optical modulation system for transmitting modulated optical light comprising an optical modulator and an automatic bias controller, the modulator having an output comprising an output arm through which modulated light is transmitted and a difference arm complementary to the output arm, the automatic bias controller comprising: a driver for providing an electrical data signal to the modulator; bias means for providing a bias voltage to the modulator; processing means for providing a low frequency digital modulation signal; a digital to analogue converter for converting the digital modulation signal to an analogue modulation signal and providing the analogue modulation signal 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 for detecting the intensity of light emitted in the difference arm of the modulator; and an analogue to digital converter arranged to convert the output of the intensity detection means to a digital intensity signal and provide the digital intensity signal to the processing means; wherein the processing means is arranged to analyse the digital intensity signal and instruct the bias means to adjust the bias voltage on the basis of the analysed signal.