A linearity interrogation technique with enlarged dynamic range for fiber Bragg grating sensing

An exact linearity interrogation technique with enlarged dynamic range for fiber Bragg grating (FBG) sensor has been analyzed theoretically and demonstrated experimentally. The technique bases on two matched FBGs for receiving the reflected signal from the sensor FBG and two photodiodes (PDs) for collecting the reflected signal from the two receiver FBGs. The linear expression between the nature logarithm of the output ratio of the two PDs and Bragg wavelength of the sensor FBG is obtained on the condition that the bandwidths of the two receiver FBGs being equal to each other. The wavelength of the sensor FBG can be interrogated simply and accurately by the linearity technique according to the expression. In addition, a new tunable paralleled matched gratings interrogation scheme is proposed. The interrogation range can be enlarged and multiple FBG sensors can be interrogated simultaneously with the tunable interrogation scheme.     

Differential reflectometry of FBG sensors in the wide spectral range

The paper presents a reflectometric technique for interrogation of multiple fiber Bragg grating (FBG) sensors based on conventional optical time domain reflectometry (OTDR). The method proposed rests on the differential measurement of FBGs’ response to a short probing laser pulse. Implementation of differential measurement principle using several reference FBGs allowed us to eliminate the susceptibility of the system to intensity fluctuations as well as to increase the measurement range as compared to the previous developments. The experimental threshold sensitivity amounted to ∼50 microstrain with the measurement range being defined by the number of reference FBGs and limited only by optical fiber tensile strength. Due to its simplicity, efficiency and usage of conventional OTDR equipment the proposed FBG interrogation technique can find a wide range of applications dealing with strain and temperature measurements.     

Experimental investigation of pre-irradiation effect on radiation sensitivity of temperature sensing fiber Bragg gratings

The effect of pre-irradiation on radiation sensitivity of fiber Bragg gratings(FBGs) is verified experimentally.FBGs are fabricated in photosensitive optical fibers and single mode fibers with Ge-concentration in a range from 3 mol% to 23.37 mol% in the core.In experiments,the FBGs are subjected to twice γ-radiation exposures to a Co60 source at a dose-rate of 0.1 Gy/s up to a total dose of 50 kGy.Pre-irradiation treatment can reduce the temperature sensitivity variation of FBGs by 18.12%-35.91%,as well as Bragg wavelength shift(BWS) by 8%-27.08 %.Our research demonstrates that pre-irradiation treatment is a feasible method to improve the radiation tolerance of FBGs.     

中心波长1080 nm的高功率光纤光栅研制与测试

介绍了基于紫外光侧写和相位掩模法制作双包层光纤光栅的工艺,制作了一对中心波长1080 nm的光纤光栅,测试光谱得到其反射谱带宽分别为2 nm和1 nm。采用自制的光纤光栅搭建了一个高功率光纤振荡器,得到最高502 W的激光输出,并测试了输出激光的光谱和光束质量。     

Sensing properties of fiber Bragg gratings in small-core Ge-doped photonic crystal fibers

We report about fiber Bragg gratings (FBGs) inscribed in two different types of small-core Ge-doped photonic crystal fibers with a UV laser. Sensing properties of the FBGs were systematically investigated by means of demonstrating the responses of Bragg wavelengths to temperature, strain, bending, and transverse-loading. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. Moreover, the bending and transverse-loading properties of the FBGs are sensitive to the fiber orientations. The reasonable analyses for these sensing properties also are presented.     

用超磁致伸缩调谐光纤光栅的光分/插复用器

提出并研究了一种新型多信道切换的全光分/插复用器,它主要由光纤Bragg光栅(FBG)和一对光环行器组成.采用了一种高效的超磁致伸缩材料(GMM)使FBG产生有效的Bragg波长偏移.用控制电流来调控FBG的应变和Bragg波长偏移.用4只相同的FBG与波长叠加技术相结合,可建立能提供15种不同下路信道方式的OADM.     

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser's peak powers can get 3.1 mW above and have a good stability.     

A Distributed Fibre Bragg Grating Sensor Interrogator Employing a Reformative Arrayed Waveguide Grating

We present an interrogating technique employing a reformative arrayed waveguide grating without output waveguides in combination with a linear charge coupled device. A simple and effective data processing method called area equalized point is used to improve the system resolution. The simulation results show that the wavelength shift of a fibre Bragg grating with temperature can be precisely measured by this interrogation technique. The temperature accuracy and wavelength resolution of the sensor system are smaller than 0.08℃ and 0.8pm, respectively. If the FBG 3dB-bandwidth is 0.2nm with the wavelength spacing between two adjacent FBGs of 1.4 nm, the temperature and wavelength errors caused by crosstalk are respectively 0.01℃ and 0. 1 pm.     

Chirped fiber Bragg gratings with arbitrary group delay responses using stepped-stretching fiber method

We present the design and development of piece-wise stepped-chirp fiber Bragg gratings (FBGs) with arbitrary group delay responses using a uniform phase mask in a pre-stretched fiber. The method involves writing a series of sub-gratings on a pre-stretched fiber whose length is varied during the UV exposure process. Two motorized stages are employed to control the length of the pre-stretched fiber in order to adjust the grating pitch at each writing step to achieve piece-wise stepped chirping of the FBG. To demonstrate the effectiveness of the method to produce chirped FBGs with arbitrary group delay responses, a linear-chirp FBG and a quadratic-chirp FBG were fabricated, and their measured performances agree well with analytical predictions. PACS 42.81.-i; 42.79.Dj; 42.79.Ci     

Quasi-distributed temperature sensor combining Fibre Bragg Gratings and temporal reflectometry technique interrogation

Quasi-distributed sensors based on Fibre Bragg Gratings (FBG) usually deal with the concatenation of FBGs of different Bragg wavelengths analyzed through wavelength-sensitive devices. In these sensors, a given wavelengths range is dedicated to one particular FBG. The number of sensing points is directly limited by the source and detector spectral ranges, and by the wavelength spacing between two gratings. This spacing is linked to the maximum possible excursion of the physical parameter to be measured-before superimposition of the reflection spectra of the FBGs.In this paper, an original interrogating device is presented, that allows a very large number of concatenated gratings to be addressed. In this scheme, identical FBGs (same Bragg wavelength and same low reflectivity) are interrogated by the Optical Time Domain Reflectometry technique, for which a commercial device has been extended to a wavelength-tunable system, within an automated experimental set-up. Detection and localization of an important amount of sensing points along a unique optical fibre is demonstrated. Repeatability measurements did exhibit the very good accuracy of the presented sensor.     

Customized MCVD fabrication of different application-type silica optical fibers and their FBG inscription characteristics

We report here the experimental realization of Fiber Bragg Gratings (FBG) of desired specifications in different application-types of in-house fabricated silica optical fibers, namely, standard telecom fiber of type SM-28, Er³⁺-doped SiO₂–GeO₂ fiber and photosensitive high GeO₂ fiber. Fibers for this purpose were fabricated by customizing the process variables of the Modified Chemical Vapor Deposition (MCVD) technique used for our laboratory fabrication of optical fibers. To check the performance of the drawn fibers in terms of FBG characteristics, gratings were written by exposing a short length of fibers to interference fringes derived from a frequency-doubled Ar-ion laser using a modified two-beam interferometer system in single phase-mask configuration. Results of inscribing selected wavelength FBGs demonstrate the efficacy of our approach in achieving, reproducibly, high-quality FBGs in all application-fibers.     

大模场啁啾光纤光栅的光谱特性

 将一种矩阵算法拓展应用于数值求解多模耦合模微分方程, 并使用该矩阵算法对大模场啁啾光纤光栅的光谱特性进行了理论研究。结果表明, 大模场多模光纤光栅因模式的自耦合和互耦合而使反射谱存在多个反射峰, 这与单模光纤光栅的反射谱不同。由于光栅周期存在啁啾, 大模场光纤光栅的反射峰分裂, 且峰值反射率减小。使用高斯切趾函数可使反射峰分裂在一定程度上得到改善。     

Switchable dual-wavelength passively mode-locked fiber ring laser using SESAM and cascaded fiber Bragg gratings

We propose and demonstrate an efficient and simple wavelength switchable dual-wavelength passively mode-locked fiber ring laser based on a semiconductor saturable absorber mirror (SESAM) and a cascaded sequence of fiber Bragg gratings (FBGs). The efficient self-starting mode-locked operation was realized with a SESAM. Dual-wavelength pulses with a wavelength spacing of 12.49 nm were obtained which was determined by the reflection peaks of the FBGs used in the experiment. In addition, by rotating the polarization controllers (PCs), the switchable dual-wavelength operation was simply achieved via exploiting wavelength-dependent loss mechanism.     

弯曲光纤布拉格光栅靶式流量传感器的研究

设计了一种基于光纤布拉格光栅(FBG)的弯曲靶式流量传感器,采用COMSOL软件仿真了弯曲靶臂受力时的应变分布规律,并将两支FBGs分别粘贴于靶臂的外侧和内侧进行应力测试,仿真与实验结果表明在外力作用下靶臂外侧和内侧分别产生拉应变和压应变,FBGs反射中心波长产生红移和蓝移。同时,测试了该结构的温度特性,在20 ℃~40 ℃两支FBGs反射中心波长均与温度呈线性关系,从而可消除温度对测量结果的影响。随后搭建了弯曲靶式FBG流量传感器测量装置,在0~800 L/H范围内的测量结果表明,两支FBGs反射中心波长与水流量呈较好的线性关系,其流量灵敏度为48 L/H。