Ultrahigh-Resolution Electro-Optic Vector Analysis for Characterization of High-Speed Electro-Optic Phase Modulators

We propose and experimentally demonstrate an electro-optic vector analyzer (EOVA), which measures not only the magnitude but also the phase responses of high-speed electro-optic phase modulators with potentially 100-GHz measurement range and sub-Hz frequency resolution, for the first time to the best of our knowledge. The key component in the EOVA is an accurately calibrated phase modulation to intensity modulation (PM-IM) convertor, which converts the phase-modulated signal generated by the phase modulator under test into an intensity-modulated signal. After simply direct photodetection in a photodetector, the magnitude and phase information is extracted in the electrical domain. Removing the responses of the PM-IM convertor and the photodetector from the measured overall responses, the magnitude and phase responses of the phase modulator are achieved. The proposed EOVA is immune to the residual amplitude modulation in the phase modulator when an optical Hilbert transformer serves as the PM-IM convertor. In an experiment, the magnitude and phase responses of a lithium niobate high-speed phase modulator from 100 MHz to 42 GHz are precisely measured with a frequency resolution of 10 MHz.