Dual-Channel Linear Optical Sampling for Simultaneously Monitoring Ultrafast Intensity and Phase Modulation

This paper proposes a novel optical sampling technique for monitoring ultrafast signal waveforms. The dual-channel sampling system, which employs two parallel interferometers offset by a slight relative delay, enables us to observe not only intensity but also phase (frequency) modulation without any restriction as regards signal coherence. The proposed method, based on linear interaction with local short-pulses, also allows the measurement of ultrafast signals without any electrical bandwidth limitation. The performance advantages of the proposed method are clarified through experiments, in which we successfully observe the intensity and frequency modulation of 10-Gbit/s gain-switched laser diode pulses and 160-Gbit/s optical time-division multiplexing signals, whose coherence time is much shorter than the sampling period.