Operation of optical modulators

Abstract

A method of, and an apparatus for, operating an optical modulator employ an optical attenuation versus voltage response which is cyclic and which includes an input to which the application of a bias voltage moves the modulator's response along the voltage axis to maintain the modulator's response at a desired voltage position. The apparatus comprises a bias voltage generator for generating a bias voltage which comprises the sum of a first and a second voltage component. The first component is fixed during normal operation and is selected to correspond to the expected bias voltage required for maintaining the modulator's response at a desired voltage position. The apparatus further comprises circuitry for detecting the position of the modulator's response and adjusting the second voltage component to maintain the response at the desired voltage position. Additionally, the apparatus includes a control circuit for detecting when the bias voltage approaches the limit of the available bias voltage range; a fixed voltage generator for adjusting the first voltage component until it is equal to the sum of the bias voltage and a voltage corresponding to one or more half cycles of the modulator's response; and a variable voltage generator for setting the second voltage component to zero.