High Sensitivity Balloon-Like Interferometer for Refractive Index and Temperature Measurement

Abstract

An all-fiber high-sensitivity modal interferometer formed by a bent standard single-mode fiber (SMF) has been presented and demonstrated, which can be used to measure refractive indexes (RIs) of solutions and temperature. The interferometer has a simple and compact structure built with a bent bare SMF mimicking a balloon shape. Because of the curvature of bent fiber sensor, modal interference effect would occur when light propagates from the fiber core into the cladding. The measurement is achieved by monitoring the spectral shift of the modal interference. The performances of the interferometers with different bending diameters and sensitive lengths are experimentally investigated concluding the optimal bending radius as 4 mm and sensitive length 16 mm. In the RI range of 1.3493-1.3822, the corresponding sensitivity and detection limit are 225.95 nm/RIU (refractive index unit) and 3.2×10 −4 , respectively. The temperature sensitivity and detection limit of 0.418 nm/°C and 0.173°C are achieved, respectively.Index Terms-Balloon-like interferometer, bent single-mode fiber, refractive index (RI) sensing, temperature sensing.

High-Sensitivity Refractive Index Sensor Based on a Cascaded Core-Offset and Macrobending Single-Mode Fiber Interferometer

“…Bending optical fiber is a simple and effective method to fabricate optical fiber RI sensors, which could achieve high sensitivity and maintain the good mechanical strength. Recently, several bent single-mode fiber-based RI sensors have been presented (Wang et al, 2009a;Ladicicco et al, 2011;Zhang and Peng, 2015a;Zhang and Peng, 2015b;Zhang et al, 2015;Fang et al, 2016;Liu et al, 2016;Gong et al, 2017;Yu et al, 2019). Wang et al (2009a) proposed an intensity demodulated RI sensor based on the macrobending single-mode fiber; however, the intensity demodulated sensor is easily affected by the fluctuation of light source and the external environments.…”

“…In the same year, the same group employed two U-shaped structure fibers with different macrobending radii to realize a dual-channel optical fiber refractometer, and the RI sensitivity can reach 245 nm/RIU (Zhang and Peng, 2015a). Liu et al, (2016) proposed a balloonlike fiber interferometer for RI and temperature measurement, and the RI sensitivity reached 225.95 nm/RIU. Yu et al (2019) improved the sensitivity of the core-offset fiber structure MZI by bending, and a sensitivity of 358.039 nm/RIU was obtained.…”

Compact and high sensitivity low‐temperature sensor based on coreless silica fiber Mach‐Zehnder interferometer

“…For temperature sensing, there are several techniques have been used or proposed previously including fiber Bragg grating (FBG) and interference mechanism based structure . Silica based FBG sensor is a very established and practical technique, however, its sensitivity is relatively low which is ∼ 10 pm/°C .…”

“…Etched and bent multimode fiber (MMF) surrounded with E7 liquid demonstrated high temperature sensitivity of 6500 pm/°C . While the balloon‐like bent technique of MMF and single mode fiber (SMF) also attained relatively high temperature sensitivity of −2060 pm/°C and 418 pm/°C, respectively. In this technique, the bent section forces light in the fiber core to spread into the polymer coating with high TOC which ensure high sensitivity due to large phase change whenever temperature is varied.…”

“…For temperature sensing, there are several techniques have been used or proposed previously including fiber Bragg grating (FBG) [1][2][3][4] and interference mechanism based structure. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] Silica based FBG sensor is a very established and practical technique, however, its sensitivity is relatively low which is $ 10 pm/8C. 3 While a conventional multimode interference (MMI) structure based on single modemultimode-single mode (SMS) fiber exhibited temperature sensitivity of $ 20 pm/8C 5 and fiber Mach-Zehnder interferometer 6 manifested temperature sensitivity of 46.8 pm/8C.…”