Vibration insensitive THz wave interferometry for characterizing optical phase shifter

Optic interferometry is a well-known measurement technique with high precision attained through the optical interference caused by the superposition of lightwaves. However, with fiber-optic interferometry, the phases of the lightwaves are susceptible to interference via the fiber fluctuation that is unavoidably induced by the environmental vibration, which makes the measurement result unstable and limits the usage scenarios of the interferometric installation. In this paper, a fiber-optic THz wave interferometer aiming for vibration isolation is presented. Due to the longer wavelength of the THz wave, the influence of optical fiber fluctuation on the phase noise is considerably suppressed. For verifying the feasibility of the fiber-optic THz wave interferometer, it is used here to measure the optical phase shift at a fiber-pigtailed thermo-optic phase shifter. The experimental results show that, compared with an all-fiber interferometer, the fiber-optic THz interferometer enables accurate measurement of an optical phase shift as well as an improved signal-to-noise ratio of interference with 6dB gain.