Ruibing Liang

Refractive index sensor using microfiber-based Mach–Zehnder interferometer

A simple and robust refractive index (RI) sensor based on a Mach-Zehnder interferometer has been demonstrated. A section of optical microfiber drawn from silica fiber is employed as the sensing arm. Because of the evanescent field, a slight change of the ambient RI will lead to the variation of the microfiber propagation constant, which will further change the optical length. In order to compensate the variation of the optical length difference, a tunable optical delay line (ODL) is inserted into the other arm. By measuring the delay of the ODL, the ambient RI can be simply demodulated. A high RI sensitivity of about 7159  μm/refractive index unit is achieved at microfiber diameter of 2.0 μm.

Microfiber Fabry–Perot interferometer fabricated by taper-drawing technique and its application as a radio frequency interrogated refractive index sensor

We propose a novel fiber Fabry-Perot interferometer (FPI) that incorporates a length of microfiber as its cavity and two fiber Bragg gratings (FBGs) as reflectors. The microfiber FPI is simply fabricated by flame-heated taper-drawing the central spot of an FBG into a section of microfiber. Ambient refractive index (RI) influences the effective index of microfiber, and thus the free spectrum range of the microfiber FPI, resulting in RI sensing. A dual-wavelength fiber laser based on the microfiber FPI is constructed, enabling radio frequency interrogation with high resolution. RI sensitivity of 911 MHz/RIU is experimentally demonstrated for microfiber FPI with equivalent diameter of 1.455 μm. Simulation results indicate that the sensitivity can be further enhanced by reducing the diameter of the microfiber.

Simultaneous wavelength and frequency encoded microstructure based quasi-distributed temperature sensor

A novel microstructure based temperature sensor system using hybrid wavelength-division-multiplexing /frequency-division-multiplexing (WDM/FDM) is proposed. The sensing unit is a specially designed microstructure sensor both frequency and wavelength encoded, as well as low insertion loss which makes it have the potential to be densely multiplexed along one fiber. Moreover, the microstructure can be simply fabricated by UV light irradiation on commercial single-mode fiber. Assisted with appropriate demodulation algorithm, the temperature distribution along the fiber can be calculated accurately. In theory, more than 1000 sensors can be multiplexed on one fiber. We experimentally demonstrated the feasibility of the scheme through building a sensor system with 9 microstructures multiplexing and with temperature resolution of 0.4°C.

Microfiber Fabry–Perot Interferometer for Dual-Parameter Sensing

We propose and demonstrate a microfiber Fabry–Perot interferometer (MFPI) fabricated by taper-drawing microfiber at the center of a uniform fiber Bragg grating (FBG). The MFPI employing the two separated sections of FBG as reflectors and a length of microfiber as its cavity is derived. Theoretic study shows that the reflection spectrum of such MFPI is consisted of two parts – interference fringes induced by multi-beam interference and reflection spectrum envelope induced by FBGs. Temperature affects both interference fringes and reflection wavelength of FBGs while ambient refractive index (RI) only influences the interference fringes, i.e., MFPI has different response to temperature and RI. Therefore, MFPI for simultaneous sensing of RI and temperature is experimentally demonstrated by tracking a reflection peak of interference fringes and the Bragg wavelength of the FBGs, which are respectively assisted by frequency domain processing and Gaussian fitting of the optical spectrum. Consequently, wavelength measurement resolution of 0.5 pm is realized.

A fiber volume strain sensor based on Mach-Zehnder interferometer

A fiber volume strain sensor based on a Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated in this paper. The sensor is fabricated by wrapping a section of fiber in the sensing arm of the MZI on a polyethylene hollow column and interrogated through measuring the FSR-1 of the MZI simply. A resolution of 3.29×10 ε is achieved when the 40mm diameter of sensing hollow column is 40mm.

FBG-microfiber-FBG cascade Fabry-Perot interferometer for simultaneous measurement of temperature and refractive index

A microfiber Fabry-Perot interferometer (FPI) which employs two fiber Bragg Gratings (FBGs) as reflection mirrors and a short length microfiber as its cavity is proposed and fabricated. Theoretic study shows that the reflection spectrum of such microfiber FPI is consisted of two parts - interference fringes induced by FPI and reflection band induced by FBGs. Temperature affects both parts while ambient refractive index only influences the first part, i.e. microfiber FPI has different response to temperature and RI. Therefore, Dual-parameter measurement is experimentally demonstrated by tracking the FSR variation and the central wavelength shift of the reflection spectrum of microfiber FPI.

High sensitivity temperature sensor using microfiber based Mach-Zehnder interferometer

A high sensitive temperature sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. Temperature measurement is achieved by immerging a section of microfiber into the refractive index (RI) liquid with a high thermo-optic coefficient. A slight change of ambient temperature will lead to the enhanced variation of the liquid index. Due to the evanescent field of microfiber, microfiber effective refractive index will be changed, and subsequently the optical length. Thus, by measuring the free spectral range (FSR) of the MZI, the temperature sensor can achieve a high sensitivity of 6.44nm/°C at the temperature of 20.6°C.

A dual-wavelength fiber laser based on a microfiber Fabry-Perot interferometer formed by Sagnac reflectors

A microfiber Fabry-Perot interferometer is constructed and employed as a reflector of a fiber laser. Dual-wavelength operation is demonstrated at its reflection peaks.