Stable continuous-wave THz vector imaging based on an optical frequency comb

Abstract

We propose and experimentally demonstrate a continuous-wave terahertz (THz) vector imaging system based on an optical frequency comb, which can avoid interference of phase noise induced by both laser and RF sources. As a benefit, the proposed THz system is capable of extracting stable amplitude and phase information and supporting robust THz imaging measurements. The system uses a phase modulator to create a wide optical frequency comb, and an intensity modulator to generate first-order harmonics of each comb line. The THz signal is photonically generated by an uni-traveling carrier photodiode (UTC-PD), and then detected in a Schottky barrier diode (SBD) detector. With respects to the reception, the THz signal is firstly down-converted into an electrical signal at the SBD based on the square-law detection and self-mixing, which is then mixed with a local oscillator (LO) and fed into a lock-in amplifier (LIA) to extract amplitude and phase information for imaging. The experimental results show the fluctuations of amplitude and phase in this system are about 0.14 mV and 3.3°, respectively. The system has a great potential in real-time THz security inspection and biomedical science.