Bias controller

A method for configuring a bias controller, having a modulator, for controlling the bias of an electro-optic modulator, the method comprising:

• (i) receiving an indication of the temperature of the modulator;
• (ii) generating a pilot tone for input to the modulator;
• (iii) generating a bias voltage for application to the modulator;
• (iv) determining a signal content of a modulated optical signal output by the modulator to recognize operation of the modulator at a required bias point;
• (v) if, at (iv), the modulator is not operating at the required bias point, adjusting the value of the generated bias voltage;
• (vi) repeating (iv) and (v) until operation at the required bias point is recognized;
• and
• (vii) for the required bias point, writing the respective value of bias voltage and the received indication of modulator temperature to the look-up table in the store of the bias controller;
• wherein the bias controller includes:
• an input for receiving an indication of the temperature of the modulator,
• a generating arrangement to generate a bias voltage to be applied to the modulator,
• a storing arrangement to store a look-up table containing, for each of a plurality of temperature points, a corresponding bias voltage to be applied to the modulator in respect of a required bias point, and
• a control arrangement to determine, with reference to the look-up table, a bias voltage to be applied to the modulator for a received indication of a modulator temperature.