고복굴절 광섬유 장주기 격자 기반 광섬유 내 마하 젠더 간섭계를 이용한 수위 및 온도 분리 측정 광섬유 센서에 관한 연구

Abstract

Here, we propose an optical fiber sensor capable of discriminating liquid level and temperature using an in-fiber Mach-Zehnder interferometer (MZI) composed of cascaded long-period fiber gratings (LPFGs) written on high-birefringence fiber (HBF). A 5.0-cm-long grating-free fiber region between the two LPFGs written on HBF, referred to as HB-LPFGs, serves as an active area of the sensor head. If the external refractive index of the active area changes due to an increase in the water level along the longitudinal direction of the sensor head, an additional phase shift of the recoupled cladding mode occurs due to the difference in the refractive index between water and air. This additional phase shift causes a wavelength shift in the interference spectrum generated by the in-fiber MZI. Due to the birefringence of HBF, the in-fiber MZI shows interference spectra with significantly different wavelengths for two orthogonal input polarization states. Its liquid level sensitivities were measured as -0.384 and -1.295nm/cm for x- and y-polarization in a water level range of 0∼5.0cm, respectively. its temperature sensitivities were also measured as ∼31.57 and ∼217.29pm/℃ for x- and y-polarization in a temperature range of 30∼60℃, respectively.