Precise terahertz-wave phase measurement based on photonics technology

We demonstrate that the photonics-based balanced self-heterodyne system enables us to measure the phase change of the continuous terahertz-wave with the theoretical uncertainties limited by the signal-to-noise ratio (SNR) of the amplitude measurement. Although our system is based on free-running lasers and fiber components, excess phase noise can be cancelled out. When the SNR was 44 dB, the standard deviation of the phase measurement was 0.37 degree, which is 10 times better than the previous method.