Robust Photonic Terahertz Vector Imaging Scheme Using an Optical Frequency Comb

In this paper, we propose and experimentally demonstrate a photonic terahertz (THz) continuous-wave vector imaging scheme using an optical frequency comb (OFC), to overcome the influence of phase noise and frequency fluctuation on extracting stable imaging information. In the experiment, a phase modulator is used to create an OFC, and an intensity modulator is employed to generate first-order harmonics for all OFC lines. The THz imaging signal is photonically generated by a uni-traveling carrier photodiode (UTC-PD), and detected by a self-mixing Schottky barrier diode (SBD) detector after passing through a sample under test. We theoretically and experimentally investigate the robustness merit of our proposed scheme in THz imaging by selecting two OFC lines, instead of either two free-running lasers or two segments of the OFC. Our experimental results show the standard deviation of amplitude and phase information in the proposed system can be significantly improved compared to other two schemes, reaching as low as about 0.032 mV and 0.54°, which represents the best amplitude standard deviation in the 300°GHz band, to the best of our knowledge. Therefore, the proposed system is promising to implement THz imaging with high resolution, flexible frequency tunability as well as high robustness.