High-sensitivity Mach-Zehnder interferometer temperature sensor based on a no-core optical fiber with a large lateral offset.

We designed and experimentally demonstrated an innovative temperature sensor based on Mach-Zehnder interference, which was formed by splicing a piece of no-core fiber (NCF) between two conventional single-mode fibers (SMFs) with a core offset. The intentional misalignment formed a gap that can be filled with ethanol, and temperature sensing was realized using the mode interference between the two distinct optical paths passing through the NCF cladding and the ethanol solution. Although the NCF length barely influenced the sensor sensitivity, it produced a major impact on the free spectral range (FSR) value. As a result, simulations were conducted and an NCF length of 620.7 µm was prepared. The sensor achieved a remarkable temperature sensitivity of 5.3574 nm/°C within the 30-36 °C range. Furthermore, the sensor boasted multiple advantages, including compact structure, high repeatability, and exceptional stability, rendering it a highly effective and versatile tool for precise thermal measurement in cell culture.