An ultrasensitive twist sensor based on parallel dual HMSF-SIs with Vernier effect

Abstract

Sensitivity has always been an important parameter for evaluating a sensor. In pursuit of high-sensitivity sensing, a highly sensitive helical microstructured fiber (HMSF) directional twist sensor based on parallel dual Sagnac interference (SI) rings with the Vernier effect has been first proposed in this paper. The Vernier effect has been realized by superimposing the transmission spectra of dual HMSF-SIs, which have slightly different free spectral ranges (FSR) between the reference and sensing arm. The FSR difference is realized by selecting different pitches of HMSF. Different pitches produce different birefringence, so the FSRs of the reference and sensing arm have a slight difference. The influences of structural parameters of the HMSF on the sensor’s performances are studied by using the finite element method (FEM). The twist sensitivity of parallel HMSF-SIs is significantly enlarged because of the Vernier effect. According to numerical simulation results, the highest twist sensitivity can be up to 3874.34 pm/(rad/m), which is orders of magnitude higher than previous studies. The proposed twist sensor can accurately identify the torsional direction and has a good linear torsional response. The novel sensor has practical application potential in twist detection.