Dispersion turning point enhanced Fizeau interferometer for micro-displacement sensing

A Fizeau interferometer exhibits high robustness, good stability, and polarization independence. However, when employed for micro-displacement detection, its sensitivity decays with the increase of cavity length. Here, we propose a dispersion turning point (DTP) enhanced Fizeau interferometer to improve the sensitivity. A piece of quartz plate is used as a beam splitter. The DTP is obtained by adjusting the length of the cavity between the reflective coating of the beam splitter and the test surface. When working near the DTP, ultra-high sensitivity to the micro-displacement is realized. In addition, when the working point deviates from DTP, we utilize the zero-dispersion point of quartz to improve the attenuation of sensitivity. A high constant sensitivity of 0.333 nm/nm is achieved within a wavelength range of 56 nm. By tuning the position of DTP, this Fizeau interferometer also possesses another advantage of adjustable dynamic range.