Fangfang Wei

Magnetic Field Sensor Based on a Combination of a Microfiber Coupler Covered with magnetic Fluid and a Sagnac Loop

This paper proposes a novel magnetic field sensor based on a microfiber coupler (MFC) combined with a magnetic fluid (MF) in a Sagnac loop formed from a polarization maintaining fiber (PMF). Thanks to the small (~2.6 μm) waist diameter of the MFC, the resulting interference is strongly influenced by the presence of the MF and this leads to the desirable high sensitivity of the structure to the applied magnetic field. The maximum magnetic field sensitivities of −100 pm/mT and −488 pm/mT have been experimentally demonstrated with the PMF lengths of 75 cm and 20 cm respectively in the range of magnetic field strengths from 0 to 200 mT. The dependence of the magnetic field orientation on the performance of the proposed sensor was also examined. The proposed magnetic field sensor is advantageous for applications requiring higher sensitivity over a wide magnetic field range.

Detection of volatile organic compounds using an optical fiber sensor coated with a sol-gel silica layer containing immobilized Nile red

A simple volatile organic compound (VOC) sensor based on a tapered small core singlemode fiber (SCSMF) structure is reported. The tapered SCSMF fiber structure with a waist diameter of 7.0 μm is fabricated using a customized microheater brushing technique. Silica based material containing immobilized Nile red was prepared by a sol-gel method and was used as a coating applied to the surface of the tapered fiber structure. Different coating thicknesses created by a 2-pass and 4-pass coating process are investigated. The experiments demonstrate that both sensors show a linear response at different gas concentrations to all three tested VOCs (methanol, ethanol and acetone). The sensor with a thicker coating shows better sensitivities but longer response and recovery times. The best measurement resolutions for the 4-pass coating sensor are estimated to be 2.3 ppm, 1.5 ppm and 3.1 ppm for methanol, ethanol and acetone, respectively. The fastest response and recovery time of 1 min and 5 min are demonstrated by the sensor in the case of methanol.

Simultaneous measurement of both magnetic field strength and temperature with a microfiber coupler based fiber laser sensor

In this paper we propose and investigate a novel magnetic field sensor based of a ring erbium-doped fiber laser combined with a fiber Bragg grating and a Sagnac loop containing a microfiber coupler and magnetic fluid. In addition to the magnetic field sensing capability, the proposed structure can simultaneously provide temperature information. Thanks to the dual-ring structure of the MFC-Sagnac loop and the FBG-assisted resonant cavity, the output has two distinct laser peaks. Experimentally demonstrated magnetic field sensitivity of one of the laser peaks is 15 pm/mT in the magnetic field range from 0 to 100 mT. The spectral position of the second laser peak is independent on the magnetic field but shifts towards long wavelengths with a sensitivity of 13 pm/°C.

Utilising a loop structure to allow a microfiber coupler with larger taper diameters to be used for sensing

This paper examines a technique that utilizes a Sagnac loop with a microfiber coupler (MFC) as a coupler which allows the MFC to operate effectively as a sensor but with larger than normal tapered fiber diameters. The proposed structure is found to be suitable for temperature and refractive index (RI) sensing. It is shown that a variation in the surrounding of the MFC RI results in a shift of the output spectrum, while a temperature variation leads to changes in the intensity of the interference dips. A decrease in the waist diameter of the MFC results in an increase in the sensitivity to temperature. For MFC structures based on a 5.6 μm and a 3 μm fiber waist diameter, the minimum transmission power level of a selected spectral dip decreases by 1.7 dB and 5.03 dB respectively, as the temperature changes from 18 °C to 44 °C. A change in the surrounding RI from 1.334 to 1.395 results in the spectral redshift of 8 nm using a 5.6 μm fiber waist diameter. By functionalizing the surface of the MFC with various materials, the structure could potentially be used for sensing of other parameters.

A spherical-structure based fiber sensor for simultaneous measurement of ammonia gas concentration and temperature

A novel fiber sensor for simultaneous measurement of ammonia gas concentration and temperature is proposed. The sensor is fabricated from two sections of single-mode fiber which are cleaved and then a fusion splicer and which is then used to fabricate spherically shaped structures at the end facets. The fusion arc is used to soften the glass which naturally assumes a spherical shape due to surface tension. A short section of multimode fiber is then fusion spliced with the two spherical-shaped ends of the single mode fibers so both the core modes and the cladding modes of the multimode fiber are excited to create two kinds of interference dips: One is created by core modes only which is not sensitive to ammonia gas since the core is isolated by the cladding so the effective refractive index of the core does not change when the refractive index of the environment changes, The other dip is created by the coupling of the core mode and cladding mod, which with a suitable coating is sensitive to ammonia gas. Silica sol-gel was prepared and coated on the fiber surface as a sensing layer for detecting ammonia gas concentration. The experimental results show that the two dips have linear wavelength shift responses but with different sensitivities to ammonia gas concentration (5.03×10-4nm/ppm for dip1 and -2.5×10- 5nm/ppm for dip2) and temperature (0.0067 nm/ºC for dip1 and 0.0149 nm/ºC for dip2. By constructing a wavelength shifts matrix for the two dips vs. ammonia gas concentration and temperature, both the ammonia gas concentration and temperature can be measured simultaneously.