Gain control for an optical modulator

摘要

There is described an optical modulation system for transmitting modulated optical light. The system comprises an electro-optic modulator having at least two arms through which light is transmitted and an imbalance electrode located on at least one arm. A current source is configured to inject current into the imbalance electrode for modifying the phase of light passing through the arm. A dither generator is configured to modulate the injected current, or bias voltage applied to at least one of the arms, with a dither signal. A phase sensitive detector is configured to detect an error in the phase of light emitted by the modulator. An operating point controller is configured to monitor the detected phase error and adjust the current injected into the imbalance arm so as to compensate for the detected error and thereby control an operating point of the modulator.

主权项

1. An optical modulation system for transmitting modulated optical light, comprising:
an electro-optic modulator having at least two arms through which light is transmitted; a voltage bias electrode located on each arm for applying bias voltage to that arm for modifying the phase of light passing through that arm; an imbalance electrode located on at least one arm; a current source for injecting current into the imbalance electrode for modifying the phase of light passing through the arm; a dither generator for modulating the injected current or bias voltage with a dither signal; a phase sensitive detector for detecting an error in the phase of light emitted by the modulator; and an operating point controller for monitoring the detected phase error and adjusting the current injected into the imbalance arm so as to compensate for the detected error and thereby control an operating point of the modulator, the required current adjustment being determined by multiplying the detected phase error by a gain; wherein the gain is modified by a compensation function selected to compensate for a non-linear relationship between the phase in the arm and the current supplied to the imbalance electrode, and the compensation function is selected to reduce the gain at low imbalance electrode currents compared to the gain at high imbalance electrode currents.