Tunable and stable refractive index sensor working near dispersion turning point

It is found that the nonlinear dispersion of optical materials can induce the interference fringe of phase compensated wave front splitting Mach-Zehnder interferometer to split at a dispersion turning point (DTP). If the resonant wavelength of a splitting fringe is closely adjacent to the DTP, it will have an ultra-high sensitivity to the refractive index of the sample and the effective thickness of phase compensator. While, the DTP is insensitive to these two parameters. Based on this discovery, by adjusting the effective thickness of the phase compensator to keep the resonant wavelength near the DTP, we design an ultra-sensitive and tunable refractive index sensor. In our experiments, not only a sensitivity up to -3.5 × 105 nm/RIU (RIU: Refractive Index Unit) is achieved, but also the dynamic range of the ultra-high sensitivity is expanded. Moreover, due to the excellent physical and chemical stabilities of the core components, and the close proximity of measurement and reference arms, the sensor possesses very good stability.