双环形腔并联瑞利后向散射式光纤陀螺

基于单环后向瑞利散射式光纤陀螺原理,提出了一种双环形腔并联的瑞利后向散射式光纤陀螺仪新结构.利用两个2×2单模光纤耦合器,建立了并联双环形腔瑞利后向散射式光纤陀螺仪的理论模型,给出了信号表达式.利用优化的环长和分光比两结构参量,分析了瑞利后向散射式光纤陀螺仪信号的输出特性.选择双环的长度分别为1500 m和1078 m,2×2光纤耦合器的耦合系数分别为95.23%和94.88%构建了测试系统,用光时域反射计(OTDR)对不同转速所探测到的后向瑞利散射信号进行测量,验证了这种新结构的可行性.同单环后向瑞利散射式光纤陀螺仪相比,双环的采用,增加了测试的有效数据,使其更有利于识别,提高了测量转速的精度.     

高Q光纤环谐振腔陀螺角速度传感研究

模拟仿真了谐振式光纤环腔的透射谱线以及鉴频曲线,得透射谱线最低谷值对应为调制谐振点,鉴频曲线的线性区为陀螺的工作范围区,线性区中点对应谐振点,可作为标度因数最大值.为了实现谐振点的高精度锁频和稳频,设计了谐振式光纤陀螺角速率测定方案,使用比例积分反馈电路实施锁频,利用正弦波扫描窄线宽激光器(线宽小于1kHz)的压电转化模块,使激光器谐振腔长发生变化,从而改变其输出频率,对谐振光纤环腔随外界环境变化同时进行跟踪和锁定.利用线宽法测试并计算出光纤环形谐振腔的品质因数值为107,对比分析了光纤环腔在谐振点和非谐振点锁定情况下的光电探测实时输出,并通过转动测试,得到两种情况下锁定后陀螺的连续转动效果.计算了光纤陀螺系统理论检测灵敏度,结果表明:谐振点锁定后转动效果对应的陀螺输出电平值为锁定非谐振点转速电平值的3倍,验证了谐振式光学陀螺谐振点锁频的重要性.     

1×7圆柱形混合棒塑料光纤耦合器

提出一种新型的使用圆柱形混合棒的 1× 7塑料光纤耦合器。该耦合器直接使用粗塑料光纤制作混合棒 ,与传统的 1× 7圆锥形混合棒塑料光纤耦合器相比省略了成本高的混合棒拉锥过程 ,因而成本较低。对混合棒失配面外接U形光纤光吸收器的 1× 7圆柱形混合棒塑料光纤耦合器进行了理论分析和实验研究 ,实验测量该耦合器的通道串音小于 - 40dB ,其耦合效率接近于 1× 7圆锥形混合棒塑料光纤耦合器。实验结果表明该耦合器是一种高性能价格比的塑料光纤耦合器     

基于游标效应增敏的全光纤液体折射率传感器

为了实现液体折射率的高灵敏度测量,提出并制备了一种基于游标效应增敏的全光纤液体折射率传感器.该传感器由法布里-珀罗传感腔和法布里-珀罗参考腔并联构成,其中,传感腔为开放腔,由单模光纤错位熔接制得,参考腔为封闭腔,由单模光纤与空芯光纤熔接制得.传感腔和参考腔的自由光谱范围相近,但不相等,双腔反射光经光纤耦合器后叠加产生游标效应,达到增敏的效果.实验结果表明,该传感器的折射率灵敏度约为9 048.78nm/RIU,约是单个传感腔的8倍.该传感器具有灵敏度高、结构简单、易于制备、成本低廉的优点,在生物医疗、环境检测等领域有潜在的应用前景.     

基于异丙醇填充和游标效应增敏的氢气传感器

采用高热光系数的异丙醇和平行连接结构,使基于Pt-WO_3敏感膜的法布里-珀罗氢气干涉仪灵敏度得到了大幅度提升。传感器的异丙醇腔由孔径126μm空心光纤和端面镀有银膜的单模光纤组成,结构紧凑且稳定。氢敏测试结果表明:干涉仪在0～2%(vol%)氢气浓度范围内的灵敏度为1.746 4 nm/%,响应速度快,重复使用性好。将两个具有微小腔长差的干涉仪通过2×2的耦合器平行连接,利用光学游标效应实现灵敏度放大,组合后的传感器达到了15.729 3 nm/%的高氢气灵敏度,并且两个干涉仪本身可以达到温度自补偿,大幅度降低了温度交叉敏感度。本文为制备灵敏度高、低成本、适用范围广的氢气传感器提供了一次有益的探索。     

飞秒激光微细加工中光耦合器参数的数值模拟

用有限差分迭代求解光束传输方程,对1×2(Y型)耦合器和2×2(X型)耦合器分路的夹角大小对分路中光束分配比例的影响进行了模拟研究.模拟结果显示：耦合器夹角控制在一定的范围内,对分路中光束能量分配影响不大;2×2耦合器对分路夹角以及波导宽度的变化敏感.为飞秒激光加工光纤无源器件的可行性做了理论上的分析.     

基于固体腔扫描法布里-珀罗干涉仪的大气温度绝对探测方法研究

大气温度是描述大气状态的重要基本特征参量之一.目前,基于Rayleigh散射的大气温度探测方法多应用于大气温度的相对探测,即温度反演时需要响应函数和校准程序.本文提出了利用固体腔扫描式法布里-珀罗干涉仪进行大气Rayleigh散射谱型的精细探测方法和残余米散射信号的抑制方法.根据Rayleigh散射谱特点,针对固体腔扫描式法布里-珀罗干涉仪的自由光谱区、固体腔几何长度、腔体介质类型、半高全宽、腔体反射率、扫描间隔等参数进行了优化设计.利用优化参数的固体腔扫描式法布里-珀罗干涉仪获取Rayleigh散射谱上离散点信息,并采用多项式插值方法获得拟合谱型,与根据标准大气模型和S6模型获得的理论谱型进行比对,大气温度探测不确定度小于0.8 K.当信噪比为10时,白天与夜晚的探测距离分别为4.5和7.9 km.该方法可实现大气温度廓线的全天时和高精度绝对探测,并对同类高光谱激光雷达分光系统研究具有借鉴意义,为我国高光谱激光雷达陆基及星载应用提供了一套可行的分光系统解决方案.     

高峰值功率脉冲激光与石英光纤耦合的空气击穿问题

 研究了15 MW峰值功率脉冲激光与600 μm芯径石英光纤耦合中存在的空气击穿现象。对聚焦区域的空气击穿现象进行了理论和实验研究,测得空气击穿阈值为0.79×10⁹ W/cm²。测得固体介质的激光损伤阈值为2.12×10⁹ W/cm²,与理论计算结果相符。提出了七合一光纤耦合器用于解决空气击穿的办法,实验测得7根光纤并束的耦合效率为67.21%。结果表明光纤耦合器可有效解决15 MW峰值功率脉冲激光与600 μm芯径石英光纤的耦合。     

适用于硅微谐振器件测量的光纤位移传感器研究

对一种适用于硅微机械谐振器件测量的光纤位移传感器进行了研究,该光纤位移传感器探头采用了单根光纤探测形式和光纤“X”耦合器结构,在微弱光电传感信号处理上采用了“锁相放大器”提取方案,可以实现对静态位移和振动位移两种场合进行测量.对该传感器的实测结果表明:该传感器测量范围为0～100 μm,测量灵敏度3.95 mV/μm,精度等级优于1%,重复性优于0.5%.为作为应用实例,运用该传感系统对一种微悬臂梁硅微谐振器件进行了测量,成功提取了硅微谐振器件的微弱谐振信号,证实了该传感器可以实现对硅微谐振器件的非接触和无损测量,并具有非接触、易调试、高灵敏度等优点.     

复合材料分层检测用光纤Mach-Zehnder干涉仪

发展了一种能够有效检测复合材料分层的光纤Mach Zehnder干涉仪。用一只2×2耦合器和一只3×3耦合器构成光纤干涉仪,输出信号经A/D转换后送入计算机,用软件进行信号解调。将此干涉仪的一个臂埋入材料内部或粘贴在复合材料表面,沿光纤逐点下压材料,通过光纤干涉仪测量出传感光纤形变的大小和方向,这样就能够有效的检测出材料内部是否存在分层。     

Real-time positioning technology of train based on optical fiber coherent Rayleigh backscattering北大核心CSCD

With the rapid growth of railway mileage in China, the degree of heavy load of railway wagons continues to increase. An interference technology based on Rayleigh backscattering signal in optical fiber was proposed by using existing communication optical cables along railway lines. When the fiber vibrated slightly, the phase and refractive index of the fiber at disturbed position changed, which resulting in the Rayleigh backscattering light. By performing differential calculation on the Rayleigh signal curves before and after the operation, the location of the interference light intensity signal corresponded to the location of the disturbances was obtained. Based on this method, the recognition and positioning of railway vehicles were realized. By collecting and analyzing the time-domain and frequency-domain signal, the signal strength, train length, the number of carriages and other characteristics were extracted, and the model of railway vehicles were accurately recognized. Compared with traditional positioning technologies, this technology could realize long-distance monitoring, and the sensing fiber was buried underground on both sides of the railway, which was conducive to the concealment and protection of optical fiber. Experimental results show that the positioning error of the system is within ±10 m, and the detection of railway speed and position within 25 km can be realized. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

相干瑞利散射海水水下温度测量技术的理论研究

海水水下温度的快速大范围测量是海洋监测的重要内容,在民用和军事领域都有着至关重要的意义,本文提出了采用相干瑞利散射方法测量海水水下温度的新方法:用宽带高速光电探测器接收本振激光和海水后向瑞利散射光相干产生的差频信号,进行傅里叶变换分析获取海水瑞利散射展宽谱,从而反演海水温度,首先从海水的热力学特性出发,对利用瑞利散射谱测量海水水下温度的基本原理进行了理论研究和软件模拟;然后对采用相干探测测量海水瑞利散射谱的测量方法进行了理论分析和软件模拟;在此基础上对瑞利散射海水水下温度测量精度进行了分析,得出当水体瑞利散射频谱半宽度测量精度为1 MHz时,测温精度约为0.35 K。     

Backscattering enhancements from Rayleigh waves on the flat face of a tilted solid cylinder in water

When the face of a finite solid elastic cylinder is ensonified by an acoustic wave, a variety of backscattering contributions associated with acoustic wave coupling into elastic waves are observed. A significant backscattering enhancement is observed for tilts such that the acoustic wave is incident on the face of the cylinder in the vicinity of the coupling angle for launching Rayleigh waves across the face. The observed backscattering indicates that the Rayleigh waves are reflected at the edge of the face and subsequently radiate acoustic waves in the backscattering direction. The measured backscattering is compared to an approximate theoretical prediction. Approximating the focusing of the Rayleigh wave after reflection at the (circular) edge by a Gaussian beam pressure distribution on the cylinder's face yields simple expressions for the amplitude which are consistent with the measurements. In the vicinity of end-on incidence, other backscattering contributions due to the reflection of waves traveling down the length of the cylinder are observed. There is also evidence of a face-traversing longitudinal wave for slightly tilted cylinders.     

Theoretical Analysis of Rayleigh Backscattering Noise in Fiber Raman Amplifiers

In this paper, a new theoretical model for Rayleigh backscattering （RB） analysis of fiber Raman amplifiers is proposed. The model includes all the interactions among the pumps, signals, and all orders of RB. The results show that the higher order RB has a negligible influence on the performance of the amplifier. The co-propagating and counterpropagating RB power of the signal grow quadratically with the net-gain of the amplifier. The signal to double Rayleigh backscattering noise ratio （OSNRDRB ） of backward-pumped FRAs is better than that of the forward-pumped ones at high net-gain level （〉 13 dB）, while at low net-gain level the OSNRDRB of the forward-pumped FRAs is slightly better than that of the backward-pumped ones.     

Full investigation of the backscattering in resonator fiber optic gyro

Resonator Fiber optic gyro (RFOG) is a high accuracy inertial rotation sensor based on the Sagnac effect. The optical fiber ring resonator (OFRR) is the key rotation sensing element. The backscattering characteristics of the OFRR are fully investigated. The Rayleigh backscattering dominates the backscattering spectrum with the input power below the threshold. High carrier suppression is crucial to reduce this Rayleigh backscattering error. Being different from the intrinsic Rayleigh scattering of the fiber, the stimulated Brillouin scattering (SBS) in the OFRR should be avoided. This is because the finesse and the resonance notch depth of the OFRR decrease for the pump depletion through the SBS process. The shot noise limited sensitivity (SLS) of the RFOG is improved by increasing the input power. Through analysis, it is found that the threshold input power is improved after phase modulation. The SLS of the RFOG is analyzed at different modulation parameters and its relevant SBS threshold. Accordingly, the optimized modulation frequency and the corresponding maximum input power are all obtained. A simple method of testing the frequency shift in the SBS is also proposed. In this method, the central frequency of the laser source is locked to the resonance frequency of the OFRR in one direction. A steady SBS light is observed and its frequency shift is measured together.     

基于微环谐振器阵列与马赫-曾德尔干涉仪的反射型滤波器性能分析

理论分析了一种将微环谐振器阵列与马赫-曾德尔干涉仪(MZI)相结合实现的反射型滤波器结构。将此结构类比为两类四端口网络级联模型,利用传输矩阵法推导出其通用函数形式,并给出单环及三环结构下的能量反射系数具体公式。通过传输函数矩阵模拟计算了取不同耦合系数值情况下的反射谱形变化,给出了原因分析及讨论。并模拟了引入传输损耗对三环结构谐振峰反射率的影响。数值结果表明:适当选取直波导与微型环以及微型环间耦合系数幅值时,此结构能够作为反射型滤波器件应用于密集波分复用(DWDM)系统,也可实现激光器反射镜面的功能;由于传输损耗增加而引起的谐振峰反射率下降程度依赖于所选取的耦合系数值。     

Mie-Rayleigh Doppler Wind Lidar with Two Double-edge Interferometers

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Mie-Rayleigh Doppler Wind Lidar with Two Double-edge Interferometers

The Mie-Rayleigh direct detection Doppler lidar (DDDL) with two double-edge etalons is presented. Fabry-Perot (F-P) etalon is used as the spectral analyzer for Doppler measurement formthe aerosol and molecule backscattered signals. The aerosol and molecular backscattering signals are separated by a polarization isolator with less signal decrement, so this system has about same accuracy as individual Rayleigh Doppler lidar or Mie Doppler lidar system. The simulation on a proposed ground-based DDDL at 532 nm shows that the velocity error is less than 2 m/s below 8 km for a 100 m vertical resolution by Mie channel and 2m/s up to 20 km by Rayleigh channel, respectively.     

多路干涉对光纤拉曼放大器噪声因数的影响

考虑了多路干涉与拉曼自发辐射噪声具有不同的谱分布特性，推导出信号的背向瑞利散射导致的多路干涉对光纤拉曼放大器噪声因数影响的解析表达式，给出了考虑多路干涉后光纤拉曼放大器的噪声因数的光学测量方法。分析了不同开关增益、不同输入信号功率、不同增益光纤背向瑞利散射情况下多路干涉对光纤拉曼放大器噪声因数的劣化程度。随着拉曼增益的增加，输入信号功率越大、背向瑞利散射越大，多路干涉的影响越大。