Phase Compensation Sensitized Wave Front Splitting Fiber Mach-Zehnder Interferometer

Based on the phase compensation, we theoretically and experimentally research into the sensitization of wave front splitting fiber Mach-Zehnder interferometer (MZI). When the optical path difference between the two arms of MZI is compensated to a small value, chromatic dispersion will play a key role in improving the refractive index sensitivity ( $S_{\mathbf {RI}}$ ). In theory, $S_{\mathbf {RI}}$ could reach infinity at a critical point. As an example, a phase compensated MZI working near the critical point of infinite $S_{\mathbf {RI}}$ is realized, achieving a sensitivity of– $1.467\times 10^{5}$ nm/RIU when the salinity is 1 PPT (Parts Per Thousand). Compared with the uncompensated wave front splitting MZI, the $S_{\mathbf {RI}}$ is improved around an order of magnitude. Much larger $S_{\mathbf {RI}}$ can be obtained by matching the refractive index and thickness of wave front splitter with that of phase compensator. It is worth noting that chromatic dispersion can also induce $S_{\mathbf {RI}}$ to vary nonlinearly with the sample refractive index.