A novel technique to measure the dynamic response of an optical phase modulator

This paper describes a novel technique that can be used to measure the frequency response of an optical phase modulator. An interesting feature of this technique is that it does not require the use of an interferometer for phase-to-amplitude conversion, thus alleviating stability and alignment problems. Instead, the electro-optically induced birefringence of the modulator and a simple polarizer are used to transform phase modulation into intensity modulation. The latter is detected with a high-speed photodiode and, for a sinusoidal modulating signal, the resulting output power spectrum is shown to be related to the actual phase modulation index by simple mathematical expressions involving Bessel functions. Using only a spectrum analyzer, the magnitude and the variations of the modulation index are measured over a broad frequency range