Abstract: Automatic bias setting circuits for multiple quantum well (MQW) diodes and optical modulators generally are described. Both digital and analog circuits are provided and techniques for utilizing such circuits for monitoring and controlling optical modulator signal quality are disclosed. In one approach, a desired modulation voltage range is determined. A bias voltage is stepped from a first predetermined voltage up to a second predetermined voltage. A maximum differential photocurrent is determined and the bias voltage corresponding to that photocurrent is then employed so that optimal optical modulator signal quality is achieved. An advantageous application of this technique is in wavelength division multiplexed (WDM) systems in which different optical modulators are operating at different wavelengths. In such a system, a different voltage bias will typically be determined for each optical modulator.