Patent ID: 8203777

Claim:
A method for controlling the bias of an electro-optic modulator, comprising: (i) receiving an indication of the temperature of the modulator; (ii) accessing a look-up table to determine a value of bias voltage corresponding to the received indication of modulator temperature, for a required bias point; (iii) generating a bias voltage of said determined value for application to the modulator; and (iv) if, at (ii), the look-up table does not contain a value for bias voltage for the required bias point, performing the following: (v) generating a pilot tone for input to the modulator; (vi) determining the signal content of a modulated optical signal output by the modulator to thereby recognize operation of the modulator at the required bias point; (vii) if, at (vi), the modulator is not operating at the required bias point, adjusting the value of bias voltage for application to the modulator; (viii) repeating (vi) and (vii) until operation at the required bias point is recognized; and (ix) storing the respective value of bias voltage and the received indication of modulator temperature in said look-up table.