A NOVEL TECHNIQUE TO MEASURE THE DYNAMIC-RESPONSE OF AN OPTICAL-PHASEMODULATOR

This paper describes a novel technique that can be used to measure the frequency response of an optical phase modulator, An interesting feat ure of this technique is that it does not require the use of an interf erometer for phase-to-amplitude conversion, thus alleviating stability and alignment problems, Instead, the electro-optically induced birefr ingence of the modulator and a simple polarizer are used to transform phase modulation into intensity modulation, The latter is detected wit h 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 Be ssel functions, Using only a spectrum analyzer, the magnitude and the variations of the modulation index. are measured over a broad frequenc y range.