Semi-open cavity in-fiber Mach–Zehnder interferometer for temperature measurement with ultra-high sensitivity

We demonstrate a semi-open cavity in-fiber Mach-Zehnder interferometer based on optical fiber tube (OFT) for temperature measurement with high sensitivity. The interferometer is composed of an OFT sandwiched between two multimode fibers, with lateral offset. The air hole of the OFT was not completely sealed and liquid is poured into the air hole through the unsealed gap. Light from the multimode fiber is split into two beams: one beam transmits directly through the silica tube while the other travels along the liquid-filled cavity. The device has ultra-high temperature sensitivity due to the much larger thermo-optic coefficient of the liquid compared with that of silica. Experimental results show that the temperature sensitivity is 6.35 nm/°C for an ethanol-filled structure.