A Hybrid Mach–Zehnder Interferometer for Refractive Index and Temperature Measurement

We fabricate and experimentally demonstrate a hybrid structured in-line Mach-Zehnder interferometer (MZI) for simultaneous measurement of refractive index (RI) and temperature. The MZI is composed of an embedded slender air cavity in a micro fiber cascaded to a piece of photonic crystal fiber (PCF). The interferometer is fabricated by fusion splicing and fused tapering. The interference spectra based on the air cavity and the PCF can be extracted through low-pass and band-pass filters, respectively. RI and temperature are interrogated through a coefficient matrix simultaneously by tracing two-dip wavelength shifts of the interference spectra. Novel structure, easy fabrication, simple system, and simultaneous measurement make it appropriate for dual-parameter sensing application.