Haiwei Fu

Large Frequency Range and High Sensitivity Fiber Bragg Grating Accelerometer Based on Double Diaphragms

A fiber Bragg grating (FBG) accelerometer based on double diaphragms is presented and experimentally demonstrated. Design, fabrication, and optimization of the FBG accelerometer are analyzed. Experimental results indicate that the FBG accelerometer provides broad flat frequency range from 50 to 800 Hz, corresponding sensitivity range from 23.8 to 45.9 pm/G, while the flatness is <;3 dB. Cross-axis sensitivity is <;2.1% of the main-axis sensitivity, dynamic resolution can reach 0.385 mG/√(Hz), and dynamic range is 80 dB. Random error of the FBG accelerometer is analyzed by using Allan variance analysis method, which is promising in cross well seismic exploration.

High-Sensitivity Mach–Zehnder Interferometric Curvature Fiber Sensor Based on Thin-Core Fiber

A simple and compact thin-core fiber (TCF)-based Mach-Zehnder interferometer (MZI) is proposed for curvature measurement. The sensor head is composed by a short section of TCF embedded between two single-mode fibers. The MZI works on the basis of interference between the core mode and cladding mode in TCF. The transmission spectrum of the sensor is analyzed by the fast Fourier transform, which indicates that the interference mainly occurs between LP01 and LP018 modes propagating in TCF. The experimental results show that the dip wavelengths in transmission spectrum decrease linearly as the curvature increase with a sensitivity of -13.53 nm/m-1. The high curvature sensitivity makes this sensor a candidate for curvature discrimination and measurement in the field of structural deformation, intelligent artificial limb, and mechanical engineering.

An In-Fiber Mach–Zehnder Interferometer Based on Arc-Induced Tapers for High Sensitivity Humidity Sensing

A new humidity sensor based on in-fiber Mach-Zehnder interferometer (MZI) is proposed and demonstrated. The interferometer consists of two arc-induced ellipsoid fiber tapers and a section of single mode fiber between them. In our humidity experiment, the relative humidity sensitivity of MZI is -0.047 nm%RH in the range of 50%-90%RH. Temperature response characteristics of this MZI are also studied, and the temperature sensitivity is 0.067 nm/°C from 27 °C to 120°C. The experimental results show that the sensor has a linear response to humidity and temperature with linear fitting of 0.993 and 0.992, respectively. The MZI presented in this paper has advantages of low cost, easy fabrication, and high sensitivity, which can be a potential detector for the relative humidity measurement.

Refractive Index Sensing of SMS Fiber Structure Based Mach-Zehnder Interferometer

A Mach-Zehnder interferometer based on single-mode-thin-core-multimode-single-mode (STMS) fiber structure for refractive index (RI) measurement is proposed and experimentally demonstrated. It works on the basis of interference between the core mode and cladding mode. Using the multimode fiber core, the transmission spectrum of STMS structure is very sensitive to RI variations of the surrounding medium. The experimental results show that the sensor possesses a high sensitivity of 148.27 nm/RIU in the RI range of 1.333-1.403 and has a good linear response to the SRI.

Low Temperature Cross-Sensitivity Humidity Sensor Based on a U-Shaped Microfiber Interferometer

A simple and sensitive optical fiber relative humidity (RH) sensor is proposed and demonstrated in this paper. The optical microfiber inter-mode interferometer is fabricated by tapering PM-elliptical core fiber down to micrometer scale in diameter, the coupling mainly occurs between the LP01 and LP11 modes. The microfiber interferometer (MFI) is fixed as U-shape, making it conveniently to measure. The RH changes are determined from the wavelength shift of the interference pattern induced by the evanescent-field interaction. Experimental results show that MFI with a thinner diameter of

Double Cantilever Beams Accelerometer Using Short Fiber Bragg Grating for Eliminating Chirp

4.7~\mu \text{m}

Humidity Sensor Based on Hybrid Fiber Bragg Grating/Abrupt Fiber Taper

offers the best RH sensitivity of 114.7 pm/RHU (per relative humidity unit) ranging from 30% to 90% and good linearity between wavelength and RH. The temperature response has also been experimentally studied, and the temperature sensitivity is 7.6 pm/°C from 30 °C to 90 °C, which indicates that this microfiber device possesses a low temperature cross sensitivity. The proposed RH sensor does not need any functional coating, with advantages of compact size and simple fabrication procedure, which make it attractive for several applications.

Liquid Level Sensor Using Fiber Bragg Grating Assisted by Multimode Fiber Core

An accelerometer based on the shorter fiber Bragg grating (FBG) is demonstrated and experimentally researched. The reflective optic spectra of FBG under inhomogeneous strain are researched by using the coupled-mode theory; the theoretical analysis demonstrates that the features of the reflective optic spectra are closely related with the chirping coefficient and the length of FBG under inhomogeneous strain. On these basics, an FBG accelerometer based on the double cantilever beams with small strain gradient is pointedly proposed. Experimental results show that the accelerometer has good response characteristic, and it provides broad flat frequency range from 4 to 30 Hz, corresponding sensitivity range from 7.76 to 10.8 pm/ms-2, while the flatness is less than 3 dB, the cross-axis sensitivity is less than 3.89% of the main-axis sensitivity, and the temperature sensitivity can be effectively eliminated by the self-symmetrical structure.

Humidity sensing of microfiber Bragg grating

A novel fiber humidity sensor based on fiber Bragg grating (FBG) cascaded with an abrupt fiber taper is proposed and demonstrated. The evanescent wave around the abrupt fiber taper varies with humidity around the sensor, so that the power of the FBG core reflection is affected by the ambient humidity. Experimental results show that the sensor has a linear response to humidity with sensitivity of 0.10-dB/%RH in the humidity range of 50%–90% RH. Such a cost-effective, compact, and reflection power detection-based humidity sensor could be a good candidate in applications.

In-Fiber Quasi-Michelson Interferometer Based on Waist-Enlarged Fiber Taper for Refractive Index Sensing

A liquid level sensor based on a fiber Bragg grating (FBG) assisted by a section of multimode fiber core (MMFC) was demonstrated. Since the coupling coefficients between the MMFC and the single-mode fiber changes and FBG reflection modes keep still as surrounding liquid level varying, the liquid level can be determined by measuring the power of the FBG reflection core mode. Experimental results show that the sensor achieves a linear sensitivity of 0.29 dB/mm within the liquid level range of 0-30 mm. The refractive index response and the temperature measurement were described. Such a simple, low-cost, and power-detect FBG-based liquid level sensor has great potential in industrial applications.