A high nonlinearity elliptical fiber for applications in Raman and Brillouin sensors

Raman and Brillouin effects have found special applications in distributed sensing for smart materials and structures. In these sensors, the fiber acts as a distributed sensor, sensing strain and temperature over a range of tens of kilometers and, at the same time, carries this information to the installation that will process them. In order to optimize the fiber to operate under the Brillouin and Raman regimes, a special elliptical fiber with small effective area has been designed, which will allow these sensors to cover longer distances and/or employ lower power lasers.     

一种提高分布式光纤测温系统空间分辨率的线性修正算法

由于分布式光纤喇曼测温系统带宽不足,导致系统的空间分辨率低;当光纤的感温区域长度接近空间分辨率的时候,系统温度响应幅值不够,导致测温不准.为解决此问题,本文提出了一种线性修正算法;在分析温度与喇曼比值关系及系统的频率响应特性的基础上,建立了该算法的数学模型,搭建了基于单模光纤的10 km分布式测温系统,并利用该算法进行了相关测温实验.实验结果与理论分析一致,该算法能有效修正3~6 m光纤的温度响应幅值,使系统测温准确度达1℃,测量时间为40 s.本算法在不增加效系统成本的同时,克服了系统带宽不足,优化了空间分辨率、温度分辨率及测量时间.     

一种提高分布式光纤测温系统空间分辨率的线性修正算法

由于分布式光纤喇曼测温系统带宽不足,导致系统的空间分辨率低;当光纤的感温区域长度接近空间分辨率的时候,系统温度响应幅值不够,导致测温不准.为解决此问题,本文提出了一种线性修正算法;在分析温度与喇曼比值关系及系统的频率响应特性的基础上,建立了该算法的数学模型,搭建了基于单模光纤的10km分布式测温系统,并利用该算法进行了相关测温实验.实验结果与理论分析一致,该算法能有效修正3～6m光纤的温度响应幅值,使系统测温准确度达1℃,测量时间为40s.本算法在不增加效系统成本的同时,克服了系统带宽不足,优化了空间分辨率、温度分辨率及测量时间.     

分立式与分布式光纤传感关键技术研究进展

光纤传感技术已广泛应用于航空航天、石油化工、电子电力、土木工程、生物医药等领域,其技术形式主要体现为分立式和分布式.分立式光纤传感技术利用光纤敏感器件作为传感器来感知被测参量的变化,光纤作为光信号的传输通道连接光纤传感器及后端的解调装置;分布式光纤传感系统基于光纤瑞利散射、拉曼散射或布里渊散射等光学效应,利用光纤本身作为传感器,可对沿途的光信号进行大范围、长距离传感.本文介绍了分立式与分布式光纤传感中主要关键技术的研究进展,并对未来的研究和发展方向进行了探讨.     

基于拉曼光谱散射的新型分布式光纤温度传感器及应用

介绍了分布式光纤拉曼温度传感器(DTS)的基本原理、发展趋势和工程应用研究状况,研究了分布式光纤拉曼温度传感器的关键技术,全面提升了DTS的性能。将拉曼放大技术应用于DTS系统,用拉曼增益部分抵偿光纤的传输损耗,使系统的传感长度达到50 km;对脉冲激光器进行211位循环编码,在接收时采用相关运算解调,显著提高系统的信噪比,使测温不确定度达到1 ℃;采用双波长自校正技术提高了系统的空间分辨率,达到2 m;在DTS系统中嵌入光开关,使测温通道成倍扩展,有效延伸了传感光纤的总长度,组成光纤传感网络。     

分布式光纤温度压力传感器设计

为了实现油田井下温度压力的全分布式测量,提出了一种基于光纤散射原理的分布式温度压力测量方法。该方法通过对普通光纤进行封装设计,制作成传感光纤。由于光纤传感器周围流体的温度和压力会对传感光纤内的散射光产生调制作用,通过光纤解调仪解调出光纤拉曼散射参数和布里渊散射频移就能够实现温度和压力的实时在线测量。实验结果表明:设计的分布式光纤温度压力传感器可以实现的温度测量分辨率为0.1 ℃,压力测量分辨率为0.07 MPa。基本满足油田井下温度压力测量的全分布式、实时在线、可靠性高、精度高、抗干扰能力强等要求。     

Fiber-optic systems for temperature and vibration measurements in industrial applications

Fiber-optic systems for temperature and vibration measurements have been developed. It is shown that using the principle of wavelength conversion in the sensor, measurement systems, in which only one fiber is used for the connection of the sensor to the instrument, can be realized. The measuring accuracy is practically independent of the properties of the fiber-optic system such as fiber length, fiber diameter and type of connectors used. These properties are very important, reducing installation problems and costs. The adoption of semiconductor technology allows batch fabrication of sensor elements. For the prototype temperature instrument an accuracy of 0·5°C was obtained in the temperature range 0 to +200°C. Fiber-optic accelerometers for vibration measurements with a resolution of 0·05 g and a dynamic range of 70 dB have been realized. The systems have been tested in different industrial environments and have properties that make them suitable for many industrial applications. Advantages of fiber-optic systems are their noise immunity, galvanic isolation and inherent intrinsic safety.     

基于圆环形薄壁截面梁的光纤光栅传感研究

提出将圆环形薄壁截面梁应用于光纤光栅传感，用一个光栅实现了对温度与应力的同时区分测量；对圆环形薄壁截面梁的应变进行了理论与实验分析，结果表明圆环形薄壁截面梁各点应变与该点角度的二倍呈余弦变化关系. 关键词： 光纤光栅传感 圆环形薄壁截面梁 啁啾     

Waveband-switchable multiwavelength mixed-cascaded phosphosilicate raman fiber lasers

In this paper, the mixed-cascaded Raman scattering has been developed to investigate multiwavelength phosphosilicate Raman fiber lasers (MRFLs). With a tunable Yb³⁺-doped double-clad fiber laser (YDCFL) as the Raman pump source, we propose a compact and waveband-switchable (from the O- to U-band) MRFL using two- or three-mixed-cascaded Raman scattering of both SiO₂/GeO₂ and P₂O₅ in a P-doped fiber. We also confirm experimentally the feasibility of the proposed mixed-cascaded MRFL. When a 1064 nm YDCFL was used to pump a spool of 1-km P-doped fiber, the compact linear-cavity MRFLs in the O- and L-band operation were obtained, respectively, based on the two- and three-mixed cascaded Raman scattering. Up to 16-wavelength stable oscillation around 1320 nm has been observed with a spacing of 0.40 nm and an extinction ratio >30 dB. 12 lasing lines around 1601 nm have also been achieved with a spacing of 0.58 nm. The multiwavelength output powers as high as 108 and 138 mW were obtained in the O- and L-band operations, respectively. The wavelength spacing of the MRFLs is flexibly adjustable, and the peak wavelength of each lasing line is continuously tunable over the wavelength spacing. In addition, the important characteristics of the mixed-cascaded MRFLs, including the linewidth broadening, the signal-to-noise ratio and the conversion efficiency, are discussed.     

Intermodal interference of LP0j modes in optical fiber with liquid core

We present intermodal interference of modes LP_0j in silica optical fiber with liquid core. An appropriate detection method is proposed for observation of intermodal interference of LP_0j modes. Measured spectral dependencies reveal a clear local minimum, where position is a function of optical fiber parameters. We focused on investigation of dependence of that minimum position on length of optical fiber with liquid core. From measured spectral dependencies the evident blue shift of local minimum is observed as length of optical fiber increases. Character of spectral characteristics correspond with intermodal interference of modes LP_0j and is demonstrated by numerical calculations. Presented intermodal interference in combination with liquid-filled core of optical fiber can be attractive for sensing applications.     

光纤分布式测温系统中基于迭代法的高准确度温度解调算法

提出了一种利用喇曼散射原理的光纤分布式测温系统中基于迭代的高准确度温度解调算法.针对于常规的反斯托克斯-斯托克斯双光路比值的温度解调算法,该迭代算法进一步校正了光纤中双光路衰减系数差对温度敏感带来的温度测量误差,尤其适用于中距离且温度场复杂的测温环境,实现了高准确度的温度测量.通过理论分析确定了该迭代法的迭代格式,测量了相应的光纤参量,并在传感样机上编写相应的代码通过实验予以验证,在0～90℃温度范围,5km测量长度输出的测温曲线符合预期的测温效果.     

光纤分布式测温系统中基于迭代法的高准确度温度解调算法

提出了一种利用喇曼散射原理的光纤分布式测温系统中基于迭代的高准确度温度解调算法.针对于常规的反斯托克斯-斯托克斯双光路比值的温度解调算法,该迭代算法进一步校正了光纤中双光路衰减系数差对温度敏感带来的温度测量误差,尤其适用于中距离且温度场复杂的测温环境,实现了高准确度的温度测量.通过理论分析确定了该迭代法的迭代格式,测量了相应的光纤参量,并在传感样机上编写相应的代码通过实验予以验证,在0~90℃温度范围,5 km测量长度输出的测温曲线符合预期的测温效果.     

Fluorescence-based temperature sensing using erbium-doped optical fibers with 1.48 μm pumping

Temperature sensing using 1.54 μm fluorescence at the transition between the energy levels⁴I_15/2 (ground state) and⁴I_13/2 generated in an erbium-doped fiber with 1.48 μm pumping is proposed. The fluorescence has a peculiar spectral profile that possesses two peaks around 1.530 μm and 1.552 μm wavelengths. The temperature-dependent fluorescence is investigated in the temperature range between -50°C and 90°C. The power ratio between the two peaks increases with an increase in temperature. The sensitivity of the ratio is 0.007/°C on average in the measured temperature range. The total fluorescence power and the absorption loss at λ = 1480 nm in the fiber decrease as the temperature increases. Optical fiber temperature sensing immune from the fluctuation in pumping power can be performed using the peak power ratio and/or the absorption loss.     

Performance of Distributed Fiber Raman Amplifier Based on Hybrid Cladding Photonic Crystal Fiber

Abstract

This article presents a feasibility study for using a hybrid cladding photonic crystal fiber as a distributed fiber Raman amplifier based transmission link with negligible confinement losses and flattened dispersion characteristics. The simulation results clearly indicate that a bit error rate of 10^?9 can be maintained at the end of a (4 × 170)-km distributed fiber Raman amplifier link operating with 40 Gbps and 0.6 dBm transmit power if 20 dBm of pump power is used for each span.     

Acoustic longitudinal mode coupling in w-shaped Al/Ge Co-doped fibre

This paper proposes a novel fibre structure aiming at distributed temperature and strain sensing. Utilizing Al₂O₃ and GeO₂ as dopants to form a w-shaped acoustic waveguide, it realizes modal coupling between longitudinal acoustic modes of its inner and outer core layers, leading to a dual-peak or multi-peak Brillouin gain spectrum. The relationship between the acoustic mode coupling properties and the fibre materials, doping concentrations and structural parameters are investigated, showing that the positions of mode coupling points in acoustic dispersion curves and the coupling intensities can be designed flexibly. A specific fibre design for the discriminative sensing of temperature and strain under a pump wavelength of 1.55 μm is given. The responses of its Brillouin gain properties on temperature and strain are analysed theoretically, demonstrating its potential for distributed fibre Brillouin sensing.     

基于游标效应的增敏型光纤法布里-珀罗干涉仪温度传感器

本文介绍了一种高灵敏度光纤温度传感器.该传感器由一小段毛细管熔接于单模光纤和一段大模场光纤之间而构成串联的两个法布里-珀罗干涉仪.由于俩干涉仪具有相近的自由光谱区,因而它们的叠加光谱会产生游标效应.实验结果显示,利用游标效应解调,该传感器的温度灵敏度可从单一空气腔法布里-珀罗干涉仪的0.71 pm/℃提高到179.30 pm/℃.该传感器结构紧凑(1 mm)且灵敏度高,具有良好的应用前景.     

Simultaneous measurement of strain and temperature based on a fiber Bragg grating combined with a high-birefringence fiber loop mirror

We present an all-fiber sensor for simultaneous measurement of temperature and strain. The sensing head is formed by introducing a fiber Bragg grating into a high-birefringence fiber loop mirror that acts as a Mach-Zehnder interferometer for temperature and strain discrimination. A sensing resolution of ±1 °C in temperature and ±21 με in strain has been experimentally achieved over a temperature range of 60 °C and strain range of 600 με.     

基于双向拉曼放大的相位敏感光时域反射仪

报道了一种基于双向拉曼放大延长相位敏感光时域反射仪分布式光纤传感系统传感距离的方法.利用双向拉曼抽运对信号光进行拉曼放大, 补偿了光纤传输损耗.实验表明, 该方法提高了整个传感光纤上信号光的分布均匀性, 实现了74 km的超长传感距离和20 m的空间分辨率, 同时, 试验了不同信号光入纤功率和抽运功率对基于双向拉曼放大的相位敏感光时域反射仪系统的影响. 关键词： 相位敏感光时域反射仪 分布式光纤传感 拉曼放大     

The Raman spectra and cross-sections of the ν2 band of H2O, D2O, and HDO

We report the experimental Raman spectra of the ν₂ band of H₂O, D₂O, and HDO in the vapor phase at room temperature. A complete interpretation of the Raman intensities is carried out employing the variational rovibrational wavefunctions obtained from a Hamiltonian in Radau coordinates and an ab initio polarizability surface at 514.5 nm. We show the importance of the rotation-vibration coupling to obtain the correct line intensities. Several tables with the assignments of the individual rotational-vibrational transitions and their Raman scattering strengths are reported. From these tables, the ν₂ Raman spectra can be simulated up to 2000 K for H₂O, and up to 300 K for D₂O and HDO.     

Raman spectra of TiO2-II,TiO2-III,SnO2, and GeO2 at high pressure

Raman spectra of the orthorhombic (II) and high pressure (III) phases of titanium dioxide at pressures to 372 kbar and effects of temperature and hydrostatic pressure on Raman spectra of the tetagonal cassiterite-like phases of TiO₂, GeO₂ and SnO₂ are described. At room temperature, the TiO₂ II–III transition is sluggish, and metastable coexistence was observed from 200 to 300 kbar. The Raman spectra of TiO₂-III imply that its primitive cell contains at least four formula units; however, the structure could not be established from the Raman spectra and available powder X-ray diffraction patterns.The temperature and pressure dependences of the spectrum of the tetragonal MO₂ phases together with bulk moduli and thermal expansion data were used to evaluate the pure-volume and pure-temperature contributions to the isobaric temperature dependence of the Raman frequencies. Large anharmonicities in TiO₂ are attributed to hybridization of the oxygen p states with the d states of the Ti ion. GeO₂, where p-electron bonding is involved, is much less Enharmonic.