High-integration optical fiber sensor with Vernier effect based on spatial beam splitting

A highly integrated optical fiber sensor is theoretically and experimentally demonstrated, which can realize optical Vernier effect by spatial beam splitting structure. The split parallel beams could be generated by spliced non-equal-diameter hollow-core fibers (NED-HCFs). By optimizing mode-field distribution and self-imaging effect, the fringe visibility (FV) of the Vernier envelope can be enhanced to 5.11 dB. Experimental results show that the central air-waveguide has a high-pressure sensitivity of 43.42 nm/MPa, while the cladding-waveguide presents the immunity of wavelength to external pressure. The measured temperature sensitivity coefficients are -108.2 pm/celcius for Vernier envelope, 11.5 pm/celcius for cladding-waveguide. Therefore, the simultaneous measurement of pressure and temperature can be realized by using the proposed structure based on dualparameter sensitivity matrix. Meanwhile, the sensor has a fast pressure response of 0.021 s due to the opencavity microchannel. The proposed sensor provides a new idea for the design of optical fiber structures based on Vernier effect.