Cost-Effective Mach-Zehnder Interferometer Liquid Refractive Index Sensor Based on Conventional Polymer Strip Waveguide

We propose and demonstrate a cost-effective liquid refractive index (RI) sensor in polymer materials by employing a Mach-Zehnder interferometer (MZI) formed with the conventional strip waveguide. The proposed sensor can attain high sensitivity by choosing a suitable reference arm length to reduce optical path difference (OPD) between the two arms of the employed MZI. Our fabricated devices, which have the same sensing arm length of 7900 μm but different reference arm lengths of 7900.0, 7942.5, 7950.9, 7962.2, and 7969.5 μm, respectively, exhibit the maximum RI sensitivities of 33662.8 nm/RIU, and almost the same detection range (DR) of 0.0041 ± 0.0002 RIU.