Yinping Miao

Relative Humidity Sensor Based on Tilted Fiber Bragg Grating With Polyvinyl Alcohol Coating

A relative humidity (RH) sensor based on tilted fiber Bragg grating (TFBG) is proposed by utilizing polyvinyl alcohol (PVA) as the sensitive cladding film. RH increasing in the PVA coating will result in reduction of refractive index. Due to the TFBGs sensitivity to ambient refractive index, the spectral properties of PVA-coated TFBG are modified under exposure to different ambient humidity levels ranging from 20% to 98% RH. The transmission power of TFBG has different linear behaviors for two different humidity ranges (20%-74% RH and 74%-98% RH), and the sensitivity for each humidity range reaches as high as 2.52 and 14.947 dBm/%RH, respectively. Combining the advantages of optical fiber grating and PVA as a smart material, this design involves simple configuration, low cost, compactness, a small degree of hysteresis, stability, and wide dynamic sensing range as well. Therefore, the sensor could be applied in real-time RH monitoring for normal as well as extremely humid environments.

Dynamic Temperature Compensating Interrogation Technique for Strain Sensors With Tilted Fiber Bragg Gratings

In this letter, we propose a novel method of edge filter linear demodulation using tilted fiber Bragg gratings (TFBGs) in a fiber sensor system. Based on the filter characteristics of TFBGs and the same temperature characteristics as the FBG, the strain sensor demodulation system with dynamic temperature compensation can be achieved. An experimental system is built up to achieve one or multichannels of sensor demodulation. The experimental results were analyzed in detail. Using this method based on intensity, linear demodulation with a bandwidth of 6 nm can be achieved. The advantages of this system are an all-fiber design, quasi-static and dynamic operation, and potential high-speed demodulation.

Research on pure bending characteristic of tilted fiber Bragg grating

In this letter, we propose a novel structure of the pure macro-bending sensor based on the tilted fiber Bragg grating (TFBG). The TFBG located in the half circle with the different diameters is bent at a constant angle with respect to the tilted grating planes. With the variations of the curvature, the core-mode resonance is unchanged and the transmission power of cladding modes detected by the photodiodes varies linearly with curvature, while the ghost mode changes by the form of two-order polynomial. So we can use the transmission power of ghost mode or other cladding modes to detect bending curvature as shape sensor. From a practical point of view, the sensor proposed here is simple, low cost and easy to implement. Moreover, it is possible to make a temperature-insensitive shape senor due to the same temperature characteristic between the core mode and the cladding modes.

Enhanced sensitivity refractive index sensor using tilted fiber Bragg grating with thinned cladding

Short-period fiber Bragg gratings with gratings planes tilted at an angle 8° corresponding to the fiber axis show core mode and a large number of cladding-mode resonances in transmission. The differences between the cladding-mode resonance and the core-mode resonance are used to detect the variation of the surrounding refractive index; this refractive index sensor is immune to temperature effects by experimental demonstrations. After the cladding of the tilted fiber Bragg grating was etched by the hydrofluoric, TFBGs with different diameters and different-order cladding modes were investigated; the sensitivity of a TFBG to the external index can be significantly improved by reducing the cladding radius. Enhanced sensitivity and accuracy are achieved when the surrounding refractive index changes between 1.333 and 1.4532.

Synthesis of fiber Bragg grating parameters from reflectivity with probabilistic global search Lausanne

A simple and accurate new method for synthesis of fiber gratings with advanced characteristics is proposed. By combining a new direct stochastic algorithm for global search called probabilistic global search Lausanne (PGSL) and transfer matrix method, we obtain a promising method synthesizing the physical parameters of a fiber Bragg grating (FBG) structure from its reflectivity. The method can be applied over uniform and nonuniform FBGs, and would be useful for other inverse problems. To demonstrate the effectiveness of the method, the synthesis of a fiber Bragg grating with triangular spectrum is presented.

Simultaneous measurement of surrounding temperature and refractive index by the tilted fiber Bragg grating

Simultaneous independent measurement of surrounding refractive index (SRI) and temperature using the tilted fiber Bragg grating is proposed and experimentally demonstrated. Core mode is sensitive only to the temperature while cladding modes are sensitive to the temperature and SRI, theirs temperature sensitivities are equal. The wavelength shifts of two kinds of modes with a change of temperature and SRI allow for simultaneous discrimination temperature and SRI effect. In addition, the sensitivity of TFBG to SRI is significantly enhanced by hydrofluoric etching clad; it can satisfy the custom-built sensitivity that the clad of TFBG was etched in different degrees as well. This sensor is potential for chemical-biochemical sensing application and measuring the concentration of the chemical solutions accurately.

Temperature insensitive strain sensors based on high birefringence fiber loop mirror with a single Fiber Bragg Grating

In this letter, a novel optical sensor based on high birefringence fiber loop mirror with a single Fiber Bragg Grating, available for temperature insensitive measurement for strain, was proposed and demonstrated. Considering that the HBFLM (high birefringence fiber loop mirror) and the conditional Fiber Bragg Grating have different response to strain and temperature, respectively, we can detect both the peak wavelength shift of these two devices. So we can build a lineal matrix equation between the perturbation of the surrounding and the shift of the transmission spectrum. Compared with conditional sensors for simultaneous measurement, this kind of sensor has several advantages, including simple configuration, low cost and easy to be fabricated.

A novel high-birefringence fiber loop mirror electric current sensor

A novel electric current sensor based on a high-birefringence fiber loop mirror(HBFLM) and a kind of magnetostrictive material rod(MMR) is demonstrated theoretically and experimentally. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The HBFLM is used as the sensor head and the linear filter simultaneously. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The rod will have elastic lengthening along the direction of the magnetic field when the uniform magnetic field changes, which will lead to a change of transmission intensity of the HBFLM filter, thus the variation of the electric current can be determined via the laser wavelength within the quasi-linear transmission range of the HBFLM filter. The sensitivity reaches 0.0153/100mA, the resolution reaches 10mA. Comparing with the previous fiber-optic electric current sensor, it has nothing with the linear birefringence based on Faraday effects in the previous fiber-optic electric current sensor. Comparing with the expensive and complex FBG electric current, the sensing signal can be directly detected by a photodiode(PD) and complicated demodulation devices are avoidable. The advantages of the electric current include optical power detection, simple and smart structure, high sensitivity, low cost, and good repeatability, etc.

Chirp tuning of a dual-wavelength fiber Bragg grating by using a loop thin-wall section beam

In this paper, for the first time to our knowledge, we proposed and demonstrated a novel method to introduce large chirp to a dualwavelength fiber Bragg grating (FBG) realized by gluing the grating to the outer surface of a loop thin-wall section beam (LSB). The bandwidth of the grating can be tuned through changing the force while the fiber grating locates at different special positions. when the positional angle θ = 45 and the LSB applied an approximately 6 kg mass, the dual-wavelength FBG was turn into a chirp grating with about 3nm bandwidth. The experimental results are coincident with the theoretical analyses.

Research on fiber sensor demodulating technique using tilted fiber Bragg gratings

Tilted fibre Bragg grating (TFBG) belongs to short-period gratings family; there is core mode and a lot of cladding modes in the transmission spectrum. According to the special structure and coupling characteristic of the TFBG, we propose a novel method of edge filter linear demodulation using tilted fiber Bragg gratings in a fiber sensor system. The results show that the widely linear range of katabatic edge (1505nm~1535nm) and an assurgent edge (1545nm~1565nm) can be used in edge filtering; the thermal characteristic of the core mode and cladding modes is similar to FBGs. Therefore, it can compensate dynamically the temperature shift of the FBG and the effect of temperature noise on the strain or other sensing signals is eliminated. The advantages of this simple system are an all-fiber design, quasi static and dynamic operation, high stability and lower cost.