Optical Heterodyne Impulse-Response Measurement of Lithium Tantalate Phase Modulator Driven by Wideband Frequency Signal

In this paper, we describe a novel optical heterodyne interferometer for characterizing phase modulation systems including a lithium tantalate phase modulator. A wideband random signal is imposed on the modulator so that the resultant beat photocurrent is modulated in phase at random. The cross-power spectrum of the fluctuating phase with the wideband random signal driving the modulator is computed to give the transfer function and the impulse response of the phase modulation system. The frequency and time response of the phase modulation are measured up to 15 MHz in a practical experiment.