Resonance Wavelength Of Long-period Fiber Grating Research Articles

A Fuzzy Approach to LPFG-Based Optical Sensor Processing and Interrogation

In this work, we report on a new interrogation method for long-period fiber-grating (LPFG) sensors. This type of sensor has been gaining increasing attention due its several interesting practical and metrological advantages. However, the LPFG optical signal is complex and could be difficult to process. We present a novel approach to the LPFG resonant wavelength detection and tracking using a multifilter LPFG interrogator. Multifilter LPFG interrogators present a great solution for LPFG sensor interrogation because there is no need for a priori knowledge concerning the LPFG sensor spectrum. We present a novel source-compensating preprocessing and a fuzzy inference system (FIS) to track the LPFG resonant wavelength. Our proposal was compared to two baseline models: a simple linear regression and an artificial neural network. Our results showed the new approach could reduce resonant wavelength uncertainty by almost three times comparing to results found in the literature.

LPG Interrogator Based on FBG Array and Artificial Neural Network

This work introduces a new method for long-period fiber grating (LPG) sensors interrogation. This proposal uses a fiber Bragg grating (FBG) array to extract spectral information of the LPG sensor and an Artificial Neural Network to process this information. The information is processed to estimate the LPG resonant wavelength, without prior knowledge on the LPG spectrum. Therefore, the interrogator is LPG-insensitive, can be easily manufactured by optical fiber sensors laboratories at low-cost and is suitable for in-field applications. We demonstrated the filter array and Multilayer Perceptron (MLP) design, which are the proposed interrogator core. Furthermore, we analyzed the interrogation performance by the Mean Squared Error (MSE), the Mean Absolute Error (MAE), and the distribution of the residuals. The results showed our proposal can estimate the LPG resonant wavelength with 2.82 nm uncertainty, considering a 95% confidence interval, over 75 nm dynamic range for several LPGs, with different spectral characteristics. Moreover, our proposal can be easily tailored for different dynamic ranges and resolutions with proper adjustments on the FBG array and MLP.

Simultaneous measurement of temperature and surrounding refractive index by superimposed coated long period fiber grating and fiber Bragg grating sensor based on mode barrier region

In this paper, simultaneous measurement of temperature and surrounding refractive index (SRI) by the superimposed coated long period fiber grating and fiber Bragg grating (SCLBG) sensor based on mode barrier region (MBR) is proposed. The sensor makes use of the different characteristics between long period fiber grating (LPFG) and fiber Bragg grating (FBG) in response to temperature and SRI, which makes it very convenient to realize simultaneous measurement of temperature and SRI. In addition, the sensitivity of the sensor to SRI is further improved by selecting an appropriate overlay thickness within the range of MBR. The simulation results show that the temperature can be accurately measured by the resonant wavelength of FBG in SCLBG. The variation of the LPFG resonant wavelength in SCLBG is caused by both SRI and temperature, and the change caused by temperature is the same as that of FBG. Therefore, the change of LPFG resonant wavelength caused by temperature can be eliminated from the change of FBG resonant wavelength, and the accurate SRI change can be obtained. According to the analysis, the sensitivity of SCLBG to temperature and SRI can reach 10pm/℃ and 2326.7nm/RIU, respectively. The linearity of the measured temperature and SRI is up to 0.999, and SRI sensitivity is at least four times higher than reported superimposed LPFG and FBG sensors. Therefore, the sensor proposed in this paper has the characteristics of high sensitivity and high linearity, which is expected to be applied in the field of sensing.

Sensitization of hybrid LPFG–FBG refractometer using double-pass configuration

We demonstrated a method to enhance the sensitivity of a hybrid arc-induced Long Period Fiber Grating (LPFG)–Fiber Bragg Grating (FBG) system using a double-pass configuration for refractive index (RI) sensing. The sensing principle is based on the interrogation of the reflected signal variation of an FBG caused by the shifting of the LPFG's resonant wavelength by changes in the surrounding medium. Standard oil with RI values ranging from 1.39 to 1.49 was used to monitor the RI response of the sensor in single-pass and double-pass configurations. Comparison of both configurations showed that the double-pass configuration utilizing an optimize-coupled LPFG has a sensitivity of 870.6dB/RIU as compared to the single-pass configuration which has a sensitivity of 457.3dB/RIU in the index range of 1.43–1.46.

Sensitivity enhancing of transition mode long-period fiber grating as methane sensor using high refractive index polycarbonate/cryptophane A overlay deposition

A highly sensitivity long-period fiber grating (LPFG) methane sensor system is presented, which was working in transition mode with high refractive index overlay deposition of polycarbonate/cryptophane A. The transparent composition coating of polycarbonate/cryptophane A was used as high refractive index overlay deposition based on automatically dip-coating technique to tune the working point of the sensor in the transition region. Effects of overlay thickness and refractive index (RI) on the LPFG's resonant wavelength were studied in order to obtain the optimal overlay thickness. For the overlay thickness of 530nm, the overlay RI of 1.5605 and the grating period of 520μm, the maximal RI sensitivity of the designed LPFG sensor could reach 3.56×103nm/RIU. The experimental results demonstrate that the new sensor has the features of high sensitivity (∼2.5nm%−1) and low detection limit of 0.2% (v/v).

High-sensitivity long-period fiber grating sensor with SAN/cryptophane A for coal mine gas detection

A high-sensitivity long-period fiber grating (LPFG) methane sensor that contains a compact and uniform styrene-acrylonitrile (SAN)/cryptophane A nanofilm is presented. The sensor is prepared by using an automatic dip-coater in a solution of cryptophane A, SAN resin dissolved in ortho-dichlorobenzene, a low-volatile solvent. The effect of film thickness on the LPFG's resonant wavelength is thoroughly investigated. The optimum sensor among the three LPFGs with different film thicknesses is directly used to detect the methane concentration in a coal mine gas sample. The results indicate that the sensors with film thicknesses of 484 to 564 nm exhibit a redshifted resonant wavelength when the methane concentration is increased from 0% to 3.5% (vol). The data demonstrates that the sensor with a film thickness of 484 nm has remarkable sensitivity (~0.633 nm%-1), and its detection limit can reach 0.2%. The methane concentrations determined by our sensor are consistent with those obtained by gas chromatography.

Research on Temperature Compensation for Long-Period Fiber Grating with Strain Property

In this paper, we demonstrate an effective method to compensate the temperature effect of long period fiber grating (LPFG). First it is found that the resonant wavelength of LPFG showes a right shift when the temperature increases while it has an opposite shift when the applied strain increases. On the basis of the characteristic, plexiglass is used to compensate the shift of the resonant wavelength induced by the tempera-ture change. The temperature characteristic of compensated LPFG has been performed. And the compensa-tion experimental result shows the temperature sensitivity of the resonance wavelength of LPFG is reduced from 55.71pm/°C to 3.7pm/°C. It is found that the method to compensate temperature is effective and prac-tical.

Perovskite-Type Oxide Thin Film Integrated Fiber Optic Sensor for High-Temperature Hydrogen Measurement

Small size fiber optic devices integrated with chemically sensitive photonic materials are emerging as a new class of high-performance optical chemical sensor that have the potential to meet many analytical challenges in future clean energy systems and environmental management. Here, we report the integration of a proton conducting perovskite oxide thin film with a long-period fiber grating (LPFG) device for high-temperature in situ measurement of bulk hydrogen in fossil- and biomass-derived syngas. The perovskite-type Sr(Ce(0.8)Zr(0.1))Y(0.1)O(2.95) (SCZY) nanocrystalline thin film is coated on the 125 microm diameter LPFG by a facile polymeric precursor route. This fiber optic sensor (FOS) operates by monitoring the LPFG resonant wavelength (lambda(R)), which is a function of the refractive index of the perovskite oxide overcoat. At high temperature, the types and population of the ionic and electronic defects in the SCZY structure depend on the surrounding hydrogen partial pressure. Thus, varying the H(2) concentration changes the SCZY film refractive index and light absorbing characteristics that in turn shifts the lambda(R) of the LPFG. The SCZY-coated LPFG sensor has been demonstrated for bulk hydrogen measurement at 500 degrees C for its sensitivity, stability/reversibility, and H(2)-selectivity over other relevant small gases including CO, CH(4), CO(2), H(2)O, and H(2)S, etc.

Zeolite thin film-coated long period fiber grating sensor for measuring trace organic vapors

A zeolite thin film-coated long period fiber grating (LPFG) sensor was developed and tested for direct measurement of trace organic vapors with straightforward operation. The sensor was fabricated by growing pure silica MFI-type zeolite (i.e. silicalite) thin film on the optical fiber grating by in situ hydrothermal crystallization. The sensor measures chemical vapor concentration by monitoring the molecular adsorption-induced shift of LPFG resonant wavelength (λR) in near infrared (IR) region. Upon loading analyte molecules, the zeolite's refractive index changes in the close vicinity of the fiber index where the λR responds with extremely high sensitivity. Because the silicalite is hydrophobic and preferentially adsorbs organic molecules, the zeolite-LPFG sensor is capable of quantifying organic vapor concentrations in lower ppm or ppb ranges without sample pre-concentration and rigorous control of operating conditions. The sensor had a much faster response speed for isopropanol than for toluene as the former has a smaller molecular kinetic size and greater diffusivity in the zeolite pores than the latter.

Zeolite thin film-coated long period fiber grating sensor for measuring trace chemical

This paper reports the development of a new zeolite thin film-coated long period fiber grating (LPFG) sensor for direct measurement of trace organic vapors. The sensor was fabricated by growing pure silica MFI-type zeolite thin film on the optical fiber grating by in situ hydrothermal crystallization. The sensor measures chemical vapor concentration by monitoring the molecular adsorption-induced shift of LPFG resonant wavelength (lambda(R)) in near infrared (IR) region. Upon loading analyte molecules, the zeolite's refractive index changes in the close vicinity of the fiber index where the LPFG has a large response to achieve high sensitivity.

Temperature compensation of long-period fiber grating for refractive-index sensing with bending effect

In this letter, we show that by properly mounting a bent long-period fiber grating (LPFG) on a suitable material, the temperature dependence of the resonance wavelength of the LPFG can be largely eliminated. With this method, we reduced the temperature sensitivity of the resonance wavelength of a typical LPFG by two orders of magnitude from -0.933 nm//spl deg/C to 0.008 nm//spl deg/C. The principle of using this mounted LPFG as a temperature-insensitive chemical concentration or refractive-index sensor is demonstrated.