Large-Dynamic Frequency Response Measurement for Broadband Electro-Optic Phase Modulators

A novel method for characterizing the frequency responses of broadband electro-optic phase modulators (PMs) by employing stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. In the proposed method, the SBS amplifies the +1st-order sideband and attenuates the −1st-order sideband of the phase-modulated signal from a PM under test. Thereby, the phase-modulated signal is converted into an optical single-sideband modulation signal. After square-law photodetection, the overall frequency responses are obtained. Removing the frequency responses of the SBS gain and the photodetector from the overall responses, the responses of the PM are thus achieved. Benefitting from the amplification of the SBS, the proposed method possesses a large dynamic range. Sub-Hz resolution and broadband measurement range are also achievable. A commercial broadband PM is experimentally characterized from 10 MHz to 50 GHz with a resolution of 5 MHz. According to the amplification of the SBS, the dynamic range is enhanced by 17.74 dB. The measurement result is verified by the conventional method utilizing optical spectrum analysis.