A bias controller for an optical modulator, said modulator including a biasable component that is operable when appropriately biased by an applied bias voltage to configure the modulator to operate at quadrature, the bias controller comprising: means for generating power signals indicative of the optical output power of the modulator; a processor operably connected to the generating means and said biasable component and arranged to receive said power signals from said generating means and to control the bias voltage applied to said biasable component; and a look up table for said modulator having stored therein a plurality of values for peak optical output power and respective predetermined values for target optical power for quadrature, wherein the processor is configured to a) vary the bias voltage applied to said biasable component and to determine from power signals received from said generating means a peak optical output power for said modulator, b) to determine in dependence upon said peak optical power a target optical power for quadrature by reference to the look up table c) to vary the bias voltage applied to the bias electrode, whilst monitoring the optical output power, until the optical output power is at the target optical power for quadrature, d) during modulation by the modulator, to monitor said optical output power; and e) to adjust said bias voltage to bring the modulator back to quadrature if said optical output power should be determined to be different from said target optical power. means for generating power signals indicative of the optical output power of the modulator; a processor operably connected to the generating means and said biasable component and arranged to receive said power signals from said generating means and to control the bias voltage applied to said biasable component; and a look up table for said modulator having stored therein a plurality of values for peak optical output power and respective predetermined values for target optical power for quadrature, wherein the processor is configured to a) vary the bias voltage applied to said biasable component and to determine from power signals received from said generating means a peak optical output power for said modulator, b) to determine in dependence upon said peak optical power a target optical power for quadrature by reference to the look up table c) to vary the bias voltage applied to the bias electrode, whilst monitoring the optical output power, until the optical output power is at the target optical power for quadrature, d) during modulation by the modulator, to monitor said optical output power; and e) to adjust said bias voltage to bring the modulator back to quadrature if said optical output power should be determined to be different from said target optical power. a) vary the bias voltage applied to said biasable component and to determine from power signals received from said generating means a peak optical output power for said modulator, b) to determine in dependence upon said peak optical power a target optical power for quadrature by reference to the look up table c) to vary the bias voltage applied to the bias electrode, whilst monitoring the optical output power, until the optical output power is at the target optical power for quadrature, d) during modulation by the modulator, to monitor said optical output power; and e) to adjust said bias voltage to bring the modulator back to quadrature if said optical output power should be determined to be different from said target optical power.