Phase Compensation Sensitized Wave Front Splitting Fiber Mach-Zehnder Interferometer

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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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{\mathbf {RI}}$ </tex-math></inline-formula> ). In theory, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{\mathbf {RI}}$ </tex-math></inline-formula> could reach infinity at a critical point. As an example, a phase compensated MZI working near the critical point of infinite <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{\mathbf {RI}}$ </tex-math></inline-formula> is realized, achieving a sensitivity of– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.467\times 10^{5}$ </tex-math></inline-formula> nm/RIU when the salinity is 1 PPT (Parts Per Thousand). Compared with the uncompensated wave front splitting MZI, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{\mathbf {RI}}$ </tex-math></inline-formula> is improved around an order of magnitude. Much larger <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{\mathbf {RI}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{\mathbf {RI}}$ </tex-math></inline-formula> to vary nonlinearly with the sample refractive index.