Optical fiber long-period grating with solgel coating for gas sensor

The novel long-period fiber grating (LPFG) film sensor is composed of the long-period grating coated with solgel-derived sensitive films. The characteristics of the transmissivity of the LPFG film sensor are studied. By analyzing the relation among the sensitivity Sn, the thin film optical parameters, and the fiber grating parameters, the optimal design parameters of the LPFG film sensor are obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10(-8). Experimentally, a LPFG film sensor for detection of C(2)H(5)OH was fabricated, and a preliminary gas-sensing test was performed.     

Spectral characteristics of a two-section multilayer long-period fiber grating sensor

A novel long period fiber grating (LPFG) sensor structure is proposed in this paper. It is constituted by coating an over-layer partially on the fiber grating. Then the LPFG has a two-section multilayer transversely distributed refractive index structure. Using coupling mode theory and transfer matrix method, the influences of refractive index, thickness and length of the coating layer on the spectral characteristics of the new type LPFG were analyzed. The simulation results show that the resonant band is split due to the particularity of the LPFG structure, and the wavelength splitting is strongly dependent on the parameters of the coating layer. This LPFG designing may solve the cross sensitive problem and then realize synchronous measurement of temperature, strain and other physical quantities.     

Highly sensitive bend sensor with hybrid long-period and tilted fiber Bragg grating

We demonstrate a new type of fiber optic bend sensor with a hybrid structure made up of a long period grating (LPG) and a tilted fiber Bragg grating (TFBG). The sensing mechanism is based on the spectrum of power transfers between the core and cladding modes from a TFBG located downstream from a LPG. We show that the curvature of a beam can be determined by the reflected power difference between the core mode and the recoupled cladding modes. We further provide design rules for the LPG and TFBG to optimize and linearize the sensor response. In addition, the temperature cross-sensitivities of this configuration are also investigated for two different types of fiber.     

基于超长周期光纤光栅的高灵敏度扭曲传感器

利用高频CO₂激光脉冲写入的周期达数毫米的超长周期光纤光栅(ULPFG)，实验研究了这种新型ULPFG的扭曲特性，发现它的某些高阶谐振波长漂移与扭曲率之间具有良好的线性关系和方向相关性，其灵敏度可达0.2244nm/(rad/m)，是高频CO₂激光脉冲写入法写入的普通LPFG扭曲灵敏度的4倍.初步的理论分析表明，新型ULPFG横截面折变的非对称性以及导模与高阶包层模之间发生的耦合使得扭曲具有方向相关性和很高的灵敏度.基于这种ULPFG独特的扭曲特性，设计了一种可 关键词： 光纤传感 光纤光栅 2激光')" href="#">CO₂激光 扭曲测量 双折射     

一种基于外差探测的光纤Bragg光栅温度传感器

提出了一种基于光纤Bragg光栅的温度传感器，阐述了光纤Bragg光栅的温度传感机理，用2个相同的光纤Bragg光栅构成折叠式Mach Zehnder(M Z)干涉仪，其中一个光栅作为参考臂，另一个作为传感臂：采用外差探测技术来测量外界的温度物理量。当温度发生变化，Bragg光栅的波长也随之改变。外差探测用来探测传感臂和参考臂由于温度变化引起的输出信号的频率差异。对其动态测量范围和灵敏度也进行了分析。     

High-sensitivity temperature sensor based on Bragg grating in BDK-doped photosensitive polymer optical fiber

A single-mode polymer optical fiber (POF) with highly photosensitive core doped with benzil dimethyl ketal (BDK) is fabricated and used for writing Bragg grating through the two-beam interference method. The Bragg wavelength of the grating is about 1570 nm, while the full-width at half-maximum (FWHM) of the reflection peak is 0.3 nm. The temperature response of POF Bragg grating is theoretically analyzed and experimentally measured in contrast to silica optical fiber Bragg grating (FBG). The result shows that the temperature character of POF Bragg grating is negative, which is opposite to the silica optical FBG. The absolute value of the temperature response of POF Bragg grating is one order of magnitude higher than that of the silica optical FBG, making POF Bragg grating appear to be very attractive for constructing temperature sensors with high resolution.     

Arbitrarily switchable multi-wavelength Yb-doped fiber lasers with phase-shifted long-period fiber grating

An arbitrarily switchable multi-wavelength Yb-doped fiber laser (YDFL) based on a phase-shifted long-period fiber grating (PS-LPFG) is proposed and demonstrated. The PS-LPFG, which was fabricated by a CO₂ laser under asymmetric exposure, acts as a spectral filter with anisotropic transmission spectrum at different states of polarization. The capability of arbitrary wavelength switching can be attributed to the combination of the polarization-dependent loss (PDL) of the PS-LPFG and the nonlinear polarization rotation (NPR) effect. The method suggests a new possibility to achieve even more wavelengths output with an all-fiber format, arbitrarily switchable and tunable capability in the Yb-doped fiber laser system in a simple, stable and well controlled manner.     

A cheap and practical FBG temperature sensor utilizing a long-period grating in a photonic crystal fiber

A whole temperature sensor in one package utilizing a fiber Bragg grating (FBG) made in a conventional single-mode fiber and which uses a long-period grating (LPG) made in a photonic crystal fiber is proposed and experimentally demonstrated. The function of the interrogation is that the wavelength change of the FBG with environmental temperature is transferred to the intensity of the output via the LPG. Utilizing the temperature-insensitivity of the LPG in the PCF, the interrogation is stable and enables a cheap and practical temperature measurement system with a wide dynamic range.     

A novel fiber Bragg grating high-temperature sensor

A novel fiber Bragg grating (FBG) sensor for the measurement of high temperature is proposed and experimentally demonstrated. The interrogation system of the sensor system is simple, low cost but effective. The sensor head is comprised of one FBG and two metal rods. The lengths of the rods are different from each other. The coefficients of thermal expansion of the rods are also different from each other. The FBG will be strained by the sensor head when the temperature to be measured changes. The temperature is measured basis of the wavelength shifts of the FBG induced by strain. A dynamic range of 0–800 °C and a resolution of 1 °C have been obtained by the sensor system. The experiment results agree with theoretical analyses.     

光纤光栅漏油传感器在石油工业健康监测中的应用

光纤光栅漏油传感器作为石油工业健康监测的智能器件具有很好的发展前景。设计了一种应用于石油工业健康监测的光纤光栅漏油传感器。通过实验得出：该光纤光栅传感器漏油报警线为1.0nm,响应时间小于3min,且该传感器具有良好的综合性能和安全使用性,能够在石油工业健康监测中起到积极的作用。     

A new phase-shifted long-period fiber grating for simultaneous measurement of torsion and temperature

A novel phase-shifted long-period fiber grating(PS-LPFG)for the simultaneous measurement of torsion and temperature is described and experimentally demonstrated.The PS-LPFG is fabricated by inserting a pretwisted structure into the long-period fiber grating(LPFG)written in single-mode fiber(SMF).Experimental results show that the torsion sensitivities of the two dips are?0.114 nm/(rad/m)and?0.069 nm/(rad/m)in the clockwise direction,and?0.087 nm/(rad/m)and?0.048 nm/(rad/m)in the counterclockwise direction,respectively.The temperature sensitivities of the two dips are 0.057 nm/℃ and 0.051 nm/℃,respectively.The two dips of the PS-LPFG exhibit different responses to torsion and temperature.Simultaneous measurement of torsion and temperature can be implemented using a sensor.The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed,and hence this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.     

Design of tunable metal-coated long-period fiber grating filter with dispersion consideration

The design of a tunable metal-coated long-period fiber grating (LPFG) filter based on the material dispersion consideration is presented. The tuning of the resonant wavelength can be achieved by heating the metal layer. Based on the coupled mode theory, the influences of the material dispersion on the transmission spectrum of the metalcoated LPFG are studied. There is a special grating period for a specific cladding mode; when the grating period is less than or equal to the special grating period, the material dispersion has weak influence on the resonant wavelength. Under such condition, the attenuation band depth corresponding to the specific cladding mode has excellent stability while the temperature changes, thus improving the filtering performances of the tunable loss filter. Further, experimental results demonstrate the validity and feasibility of the proposed tunable filter.     

Dual-channel microfluidic sensor based on side-hole fiber with two long-period fiber gratings

We propose and demonstrate a dual-channel microfluidic sensor based on a side-hole fiber(SHF)with two longperiod fiber grating(LPFG)structures.There are two air holes in the SHF,which are natural microfluidic channels.We fabricate two LPFGs(long-period gratings LPG-A and LPG-B)in the SHF with the resonance wavelengths of 1268.7 nm and 1385.8 nm,respectively.Results show that the refractive index sensitivities of LPG-A and LPG-B are?76.0 nm/RIU and?71.1 nm/RIU,respectively.One can measure the refractive index of liquid samples in two channels simultaneously.The proposed dual-channel microfluidic sensor has advantages of good linearity response,fluidic technology compatibility,and easy light input/output coupling and system integration,which helps the sensor to have a potential application in environmental detection and food safety detection.     

Nanocrystalline ZnO coated fiber optic sensor for ammonia gas detection

A cladding modified fiber optic sensor coated with nanocrystalline ZnO is proposed for ammonia gas detection. As-prepared and annealed zinc oxide (500 and 1200 °C) samples are used as the gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the ammonia concentration. The characteristics of the sensor when exposed to ethanol and methanol gases are also studied for gas selectivity. The time response characteristics of the sensor are reported.     

A simple temperature-insensitive fiber Bragg grating displacement sensor

The study on fiber Bragg grating (FBG) displacement sensor based on monitoring the back-reflected power from an array of novelly embedded FBG sensors is presented. The sensor is a uniform FBG with three sections that are embedded in different layer in a composite lamina. Its bandwidth is displacement dependent and hence its reflected power varies almost linearly with displacement and it is insensitive to temperature variation. Thus, only low-cost photodetector (PD) is required to monitor displacement. This study demonstrates a novel fiber sensor, a method of fabricated the same, and a method to achieve simultaneous multi-sensor measurement.     

Intrinsic fiber Fabry-Perot temperature sensor with fiber Bragg grating mirrors

A fiber Fabry-Perot interferometer (FFPI) sensor is formed with broadband (~3 nm, 3-dB bandwidth) fiber Bragg grating (FBG) mirrors. Repetitively modulating a distributed-feedback laser produces chirping that modulates the reflectance of the FFPI. Because the reflectance of the FBG mirrors varies with optical frequency, the fringes in the sensor reflectance modulation are distinguishable, making it possible to extend the sensor dynamic range versus that of a FFPI sensor with conventional wavelength-dependent mirrors. An ambient temperature is determined in the range from 25 to 170 degrees C with a resolution of 0.005 degrees C.     

A chiral long-period grating fabrication method based on axis-offset rotating optical fiber

Optical and Quantum Electronics - In this paper, different optimal designs of Yagi–Uda nano-antennas (NAs) are introduced and analyzed based on different element shapes to maximize the...     

Design of an ultra-broadband all-optical fractional differentiator with a long-period fiber grating

We propose an all-optical in-fiber ultra-broadband fractional differentiator. We numerically demonstrate that a long-period grating inherently performs the temporal fractional differentiation on an optical pulse propagating in the fundamental fiber mode, within a certain spectral bandwidth around the resonance frequency. The device shows a good accuracy calculating the fractional time derivatives of the complex field of THz-bandwidth optical pulses.