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.