Simple homodyne technique for the characterisation of wideband optical detectors

In this work we present a simple self-homodyne technique for the characterisation of wideband photodetectors. This technique transforms the frequency modulation of the laser diode into intensity modulation using a 2-beam interferometer. When the laser diode is modulated by a triangular signal, the power is concentrated in one beating frequency component that can be swept by changing the amplitude of the modulating signal. The experimental and theoretical results are in good agreement. As an example, with the frequency of the modulating signal equals only 15 kHz we have measured a detector response of up to 1.5MHz.