Real-time complex temporal response measurements of ultrahigh-speed optical modulators

We demonstrate a technique for direct, real-time characterization of the complex (amplitude and phase) temporal response of ultrahigh-speed (GHz-bandwidth) optical modulators. The demonstrated technique is based on pulse interferometry combined with time-frequency mapping processes using fiber linear dispersion. A new mechanism is incorporated to overcome the temporal resolution (bandwidth) limitation of the detectable modulation response in our previously reported setup. This mechanism, referred to as 'common-path temporal image magnification', lowers the required detection bandwidth by a factor of more than 10, enabling real-time single-shot waveform acquisition without loss of information using a conventional temporal digitizer. The design specifications of the proposed measurement setup are derived and discussed in detail. As a proof-of-concept experiment, real-time characterization of a complex electro-op c modulation temporal response with time features as fast as approximately 35 ps (modulation bandwidth > 40-GHz) was obtained and displayed at a video rate of 30 frames/sec.