A Sagnac Interferometer Ultraviolet Sensor Based on ZnO-Coated No-Core Fiber

Abstract

A Sagnac interferometer based optical fiber ultraviolet (UV) sensor is theoretically proposed and experimentally demonstrated in this work. A layer of ZnO film was deposited upon the surface of a silica no core fiber (NCF) using the magnetron sputtering method. Since the ZnO film was sensitive to UV, the ZnO-coated NCF was introduced into the Sagnac interferometer to help convert changes of the UV irradiance to the wavelength shifts of the interference spectrum. In comparison with the preparation of ZnO nanostructures, the ZnO film had the advantage of simple operation, high deposition rate, good adhesion and stable structure. The influence of the ZnO film thickness on the UV response was investigated, which proved that with the increase of the film thickness, the UV sensitivity decreased gradually. When the ZnO film thickness was 30 nm and the UV irradiance varied from 0 mW/cm² to 19.95 mW/cm², the designed sensor had the highest sensitivity of −124.9 pm/(mW/cm²) (R² = 0.9854) and a detection accuracy of 0.4 mW/cm². The proposed sensor has competitive sensitivity, high linearity, satisfactory repeatability and stability, which can be expected to conduct high-precision UV sensing in industrial, biomedical and military regions.