Continuous-wave THz imaging system using microwave photonic double sideband modulation

Abstract

We propose and experimentally demonstrate a continuous-wave (CW) terahertz (THz) imaging system based on microwave photonic signal generation scheme. Compared to the traditional opto-electronic THz imaging by using unmodulated lasers, our proposed system obtains the amplitude information by using microwave photonic optical double sideband modulation (DSB). As a result, the phase noise and frequency drift of the free-running laser sources are negligible. We experimentally demonstrate a THz imaging system for measuring various 3D-printed samples by using a 300 GHz DSB signal. In the experiment, the optical DSB modulation is realized with an in-phase and quadrature Mach-Zehnder modulator, and THz signals are generated by photo-mixing at a uni-traveling-carrier photodiode. The THz signals passing through the sample is received by a self-mixing-based Schottky barrier diode. The experimental results show signal-tonoise ratio (SNR) a ~25 dB . In addition, we verify that the optical DSB system operating in the linear regime is superior to the carrier-suppressed scheme, which is attributed to higher THz power and higher SNR. Therefore, the proposed scheme based on microwave photonic double sideband modulation is potentially promising in high-resolution object recognition.