A Compact Fiber Cascaded Structure Incorporating Hollow Core Fiber With Large Inner Diameter for Simultaneous Measurement of Curvature and Temperature

Abstract

A compact fiber cascaded structure for simultaneous measurement of curvature and temperature based on Fabry-Perot (FP) interference and anti-resonant (AR) mechanism is designed and experimentally demonstrated. The proposed structure is manufactured by sandwiching a segment of hollow core fiber (HCF) with large inner diameter and suitable length between two segments of single mode fibers (SMFs). Three sample sensors were fabricated with different HCF lengths. With theoretical analysis and experimental verifications, an HCF length of 1197 μm was selected for curvature and temperature experiments. The reflection fringes based on FP interference and transmission envelopes based on AR mechanism can be monitored to measure curvature and temperature variations at the same time. From experimental results, the sensitivities of curvature based on AR mechanism and FP interference are 0.2345 nm/m -1 and -0.1021 nm/m -1 , and those of sensitivities of temperature are 0.0172 nm/℃ and 0.0017 nm/℃, respectively. Therefore, the different responses in curvature and temperature based on two mechanisms enable the proposed structure to simultaneously measure curvature and temperature.

Temperature–insensitive curvature sensor based on hollow-core fiber assisted microbubble Mach–Zehnder interferometer

“…In 2022, Qi et al made FP interferometric curvature sensors by sandwiching a section of 1197 µm long HCF between two sections of SMF. The maximum curvature sensitivity was 0.2345 nm/m − 1 and the highest temperature sensitivity was 0.0172 nm/°C [19] , respectively. Recently Zhu et al used MZI with SMF-HCF-SMF ends fused into the shape of a peanut, with a maximum curvature sensitivity of -648.17 pm/m − 1 and maximum temperature sensitivity of 25.42 pm/°C [20] .…”

“…This causes the hollow part of the ber to expand, which leads to the deformation of the ber, thus affecting the experiment. Qi [19] prevents the hollow part from collapsing, weakly discharged, and manually mode several times during the fusion splicing process [21] . But this operation in question requires many manual adjustments and a lot of manual actions that are more accidental.…”

Temperature-Insensitive Two-Dimensional Vector Bending Sensor Based on Fabry-Pérot Interferometer Incorporating a Seven-Core Fiber

“…For the MMF, its core diameter and cladding diameter are 105 and 125 µm , respectively, which is just as one reflector of the FPIs. It is noted that when the fusion splicer (ATOMOWAVE SFS-A60+) is utilized to splice three fibers, manual mode and multiple weak discharges were employed for preventing the air hole collapse in COF [23]. The fusion mode was set as photonic crystal fiber (PCF)-SMF, the discharge power was lower than the standard value of 100 bit.…”

“…Some of the curvature sensors were based on intensity modulation [14]. Fiber optic interferometers have also been adopted in curvature sensing, including multimode interferometers (MMIs) [16], Mach-Zehnder interferometers (MZIs) [17]- [20], Fabry-Pé rot interferometers (FPIs) [2]- [3], [21]- [22], anti-resonant (AR) mechanisms [23]- [24], and Sagnac interferometers (SIs) [25].…”