Enhanced Sensitivity Refractometer Based on Spherical Mach–Zehnder Interferometer With Side-Polished Structure

A novel high sensitivity refractometer based on side-polished Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The configuration of the sensor is a piece of side-polished structure fiber which is sandwiched between two spherical structures. In this proposed MZI configuration, the intermodal interference occurs between the cladding modes and the core mode. Due to the effective refractive index of cladding varies with the changes of surrounding refractive index, so this structure can be used to measure the external surrounding refractive index changes. This side-polished MZI is 18 times more maximum sensitive than the MZI without side-polished, which has 213.479 nm/RIU and 730.502 nm/RIU sensitivities in the index ranges of 1.33269-1.39716 and 1.40734-1.42294, respectively. And experiments show that this refractometer is suitable for bio-chemical applications.