Correction of the Intensity-Dependent Phase Delay in a Silicon Avalanche Photodiode by Controlling its Reverse Bias Voltage

When an intensity-modulated periodic light is incident on a reverse-biased silicon-avalanche photodiode (APD), the phase of the output signal from the APD over that of the incident light is delayed. The phase delay becomes larger with decreasing incident light intensity. This kind of phase delay is a serious problem for metrology that utilizes the APD as a photodetector. To solve this problem, we propose a new correction method: for situations of low light intensity, the reverse bias voltage applied for the APD is decreased. Adjustment of the reverse bias voltage enabled us to suppress the phase delay around 60° to be less than 0.2° for an incident light intensity of 0.5 (mu)W, a modulation frequency of 600 MHz, and a wavelength of 632.8 nm.