Influence of Refractive Index Distribution on Brillouin Gain Spectrum in GeO_(2)-Doped Optical Fibers

GeO_(2) is commonly used as dopant to adjust the refractive index profile(RIP)and the acoustic velocity profile(AVP)in the fiber,thereby forming different Brillouin gain spectrum(BGS)characteristics such as Brillouin gain,acoustic mode number and peak intensity difference.When an optical fiber is used in optical fiber sensing or communication system,its BGS characteristics may play an important role in determining the performance of the system.In this paper,finite element analysis(FEA)method is used to study the influence of refractive index distribution and its corresponding AVP on the BGS in step-index,graded-index,and complex-index optical fibers.A new method has also been proposed to efficiently discriminate acoustic mode solution and obtain the new and full images of total Brillouin gain and acoustic modes number of the fiber as a function of the refractive index distribution,considering the influence of changing the refractive index difference and the geometric size simultaneously.For each type of optical fiber,the recommended parameter range is provided for optical fiber sensing and optical fiber communication.Moreover,the suitable optical fiber with close peak intensity in its multi-peak BGS is explored and achieved,which can be used in Brillouin beat spectrum detection systems to improve sensing accuracy.

Optimization of Spectral Inverters in Optical Fiber Communication Systems with Mid-Span Spectrum Inversion

In this paper, signal distortions caused by spectral inverters which are used in 10Gb/s optical fiber communication systems with mid span spectrum inversion in terms of dispersion shift fibers are analyed numerically. It is shown that there exist the optimal input signal power, fiber length and fiblter bandwidth for the spectral in verters. System transmission penalty can be minimized by optimizing these parameters.

Design of supercontinuum generating photonic crystal fiber at 1.06, 1.31 and 1.55 µm wavelengths for medical imaging and optical transmission systems

We propose broad supercontinuum spectrum generating highly nonlinear photonic crystal fiber (HN-PCF) which can be used in ultrahigh- resolution optical coherence tomography and optical transmission systems. Using full vector finite difference method, we investigated the different properties of HN-PCF. Broadband su-percontinuum spectrum is numerically calculated by using nonlinear Schr?dinger equation. Investigation showed that it is possible to obtain longitudinal resolution in a biological tissue of 1.3 μm, 1.2 μm and 1.1 μm by using picosecond continuum light at center wavelengths of 1.06 μm, 1.31 μm and 1.55 μm, respectively.

Novel Portable Oil Ingredient Instrument with Optical Fiber Link

The operation principle of a novel portable oil ingredient instrument is introduced. Using the theory of fluorescence measurement, this instrument can carry out fast and consecutive in-situ detection of oil ingredient in sea water, confirming fast and correctly the situation of oil contamination such as the concentration and the area, etc. The lowest detectable concentration for the instrument is 1×10 -8 g/ml with the precision of less than 3 %. The results of experiment and practice show that this system has well water-sealed characteristic and repeatability.

Anycast Transmission in Routing Modulation Level Spectrum Assignment (RMLSA) Problem on Space Division Multiplexing (SDM) Elastic Optical Networks (EON)

With the rise of cloud computing in recent years, a large number of streaming media has yielded an exponential growth in network traffic. With the now present 5G and future 6G, the development of the Internet of Things (IoT), social networks, video on demand, and mobile multimedia platforms, the backbone network is bound to bear more traffic. The transmission capacity of Single Core Fiber (SCFs) may be limited in the future and Spatial Division Multiplexing (SDM) leveraging multi-core fibers promises to be one of the solutions for the future. Currently, Elastic optical networks (EONs) with multi-core fibers (MCFs) are a kind of SDM-enabled EONs (SDM-EON) used to enhance the capacity of transmission. The resource assignment in MCFs, however, will be subject to Inter-Core Crosstalk (IC-XT), hence, reducing the effectiveness of transmission. This research highlights the routing, modulation level, and spectrum assignment (RMLSA) problems with anycast traffic mode in SDM-EON. A multipath routing scheme is used to reduce the blocking rate of anycast traffic in SDM-EON with the limit of inter-core crosstalk. Hence, an integer linear programming (ILP) problem is formulated and a heuristic algorithm is proposed. Two core-assignment strategies: First-Fit (FF) and Random-Fit (RF) are used and their performance is evaluated through simulations. The simulation results show that the multipath routing method is better than the single-path routing method in terms of blocking ratio and spectrum utilization ratio. Moreover, the FF is better than the RF in low traffic load in terms of blocking ratio (BR), and the opposite in high traffic load. The FF is better than the RF in terms of a spectrum utilization ratio. In an anycast protection problem, the proposed algorithm has a lower BR than previous works.

Combined Transmission Interference Spectrum of No Core Fiber and BP Neural Network for Concentration Sensing Research

To investigate wavelength response of the no core fiber（NCF）interference spectrum to concentration,a three-layer back propagation（BP）neural network model was established to optimize the concentration sensing data.In this method,the measured wavelength and the corresponding concentration were trained by a BP neural network,so that the accuracy of the measurement system was optimized.The wavelength was used as the training set and got into the input layer of the three layer BP network model which is used as the input value of the network,and the corresponding actual concentration value was used as the output value of the network,and the optimal network structure was trained.This paper discovers a preferable correlation between the predicted value and the actual value,where the former is approximately equal to the latter.The correlation coefficients of the measured and predicted values for a sucrose concentration were 1.000 89 and 1.003 94;similarly,correlations of0.999 51 and 1.018 8 for a glucose concentration were observed.The results demonstrate that the BP neural network can improve the prediction accuracy of the nonlinear relationship between the interference spectral data and the concentration in NCF sensing systems.

Monitoring the hydrolyzation of aspirin during the dissolution testing for aspirin delayed-release tablets with a fiber-optic dissolution system

The purpose of this study was to investigate the hydrolyzation of aspirin during the process of dissolution testing for aspirin delayed-release tablets. Hydrolysis product of salicylic acid can result in adverse effects and affect the determination of dissolution rate assaying. In this study, the technique of differential spectra was employed, which made it possible to monitor the dissolution testing in situ. The results showed that the hydrolyzation of aspirin made the percentage of salicylic acid exceed the limit of free salicylic acid （4.0）, and the hydrolyzation may affect the quality detection of aspirin delayed-release tablets.

Rapid analysis of piperazine ferulate tablets by optic-fiber sensing technology and the similarity of ultraviolet spectra

A rapid analysis method of piperazine ferulate tablets by optic-fiber sensing technology with UV-vis absorption spectrum was established. Qualitative and quantitative data were obtained and compared by maximum and minimum wavelength, absorbance and contrast spectra. Similarity method was used to identify authenticity of drugs. The difference of contents measured by this method and UV determination method in China Pharmacopoeia showed no statistical significance (P40.05), while the similarity can be used as a parameter to identify the authenticity of drugs.

Spectral analysis of the UFBG-based acousto optical modulator in V–I transmission matrix formalism

In this study, the V-I transmission matrix formalism （V-I method） is proposed to analyze the spectrum characteristics of the uniform fiber Bragg grating （FBG）-based acousto--opfic modulators （UFBG-AOM）. The simulation results demon- strate that both the amplitude of the acoustically induced strain and the frequency of the acoustic wave （AW） have an effect on the spectrum. Additionally, the wavelength spacing between the primary reflectivity peak and the secondary reflectivity peak is proportional to the acoustic frequency with the ratio 0.1425 nm/MHz. Meanwhile, we compare the amount of calculation. For the FBG whose period is M, the calculation of the V-I method is 4 × （2M-l） in addition/subtraction, 8 × （2M - 1） in multiply/division and 2M in exponent arithmetic, which is almost a quarter of the multi-film method and transfer matrix （TM） method. The detailed analysis indicates that, compared with the conventional multi-film method and transfer matrix （TM） method, the V-I method is faster and less complex.

基于互相关谱滑动平均的OFDR应变传感精度提升研究

OFDR在长距离大应变传感时易出现相位噪声,使得应变传感精度较差或无法还原真实应变变化。文章采用互相关谱滑动平均方法对OFDR原始互相关谱进行处理以提升应变传感精度。阐述了应变解调干扰噪声产生机理,分析了基于互相关谱滑动平均的OFDR应变传感精度提升原理,搭建了OFDR应变传感系统,在103.8m传感光纤上进行了实验验证,并讨论了不同大小的滑动平均块对结果的影响。实验结果表明,在扫频范围60nm,滑动平均块大小为1×10时,可在103.8m待测光纤实现空间分辨率为1.33cm,最大值为4000με的应变传感,应变区波长偏移量标准差显著降低。研究证明,互相关谱滑动平均方法可以有效提升OFDR系统应变解调精度。

Stress test and analysis based on SMS fiber structure with high sensitivity

Single mode-multimode-single mode （SMS） sensor is widely used for parameters measurement, such as bending, dis-placement, temperature, strain, refractive index, etc. Generally, SMS sensor has advantages of simple structure, low cost and easy layout, therefore it has become a research hotspot in recent years. In this paper, the multimode fiber with large core is used for manufacturing SMS structure with high sensitivity. Firstly, the multimode fiber with core/cladding diameters of 105/ 125 jitm has access to the system by means of single mode optical fiber. Secondly, SMS device structure is manufactured by welding the eccentric shaft of multimode optical fiber. Afterwards, mode interference effect and spectral response characteristics of the structure of single mode-multimode-single mode optical fiber are analyzed theoretically. Finally, with the help of a wide spectrum light source and a spectrum analyzer, the transmission spectra characteristics of SMS optical fiber with strain is tested. By observing the curve that the wave changes with stress, the sensitivity is calculated and it is consistent with theoretical value .

Supercontinuum Generation Enhanced by Cross-phase Modulation in Dispersion-flattened and Decreasing Fiber

Supercontinuum spectrum generation in a dispersion-flattened and decreasing fiber with two orthogonally polarized pulses was simulated and calculated. The research results indicated that the supercontinuum spectrum generated by two orthogonally polarized pulses is wider and flatter than that generated by single polarized pulse due to cross-phase modulation. The cross-phase modulation effect can enhance the supercontinuum spectrum generation. When the pump power of the input pulse is lower, the enhancement of supercontinuum spectrum generation by cross-phase modulation effect is more significant.

Effect of PMD-induced Pulse Broadening on Sensitivity and Frequency Spectrum

The PMD-induced pulse broadening may cause the degradation ofreceiver sensitivity and has negative effects on the power spectrumof received signals. The expression s of PMO-induced pulse broadeningeffects on receiver sensitivity are derived based on the concept ofman square pulse width. The effects of PMD on the spectrum ofreceived power are analyzed in detail. Finally, the scheme isdiscussed with which the poser of a certain frequency component isextracted as a feedback control signal in a PMD compensation system.

Experimental investigation on chaos generation in erbium-doped fiber single-ring lasers

In this paper,the chaotic behaviors in an erbium-doped fiber（EDF） single-ring laser（EDFSRL） are investigated experimentally by using the loss modulation method.An electro-optic modulator（EOM） made of LiNbO 3 crystal is added to the system.Thus,by changing the modulation voltage and the modulation frequency of the EOM,the freedom of the EDFSRL system is increased.The chaotic characteristics of the system are studied by observing the time series and the power spectra.The experimental results indicate that the erbium-doped fiber single-ring laser system can enter into chaos states through period-doubling bifurcation and intermittency routes.

New Test Light Spectrum Design for L/U-Band Extended Optical Fiber Line Testing System

This paper describes a new design for the test light source of an L/U-band extended optical fiber line testing system and the side-band suppresser ratio of the test light should be more than 70 dB.

宽谱光源谐振式光纤陀螺谐振特性分析

为优化宽谱光源谐振式光纤陀螺(RFOG)谐振腔设计,进行了RFOG谐振特性分析。首先,根据光场传输理论完成了宽谱RFOG光场传输特性分析,建立了宽谱RFOG谐振频差曲线模型,给出了谐振特性参数表达式。理论证明了宽谱RFOG的陀螺精细度和半高全宽约为谐振腔光谱曲线的1/2和2倍。其次,基于宽谱RFOG光场理论模型,分析了耦合器交叉耦合系数、附加损耗和谐振腔腔长等谐振腔关键光学参数对陀螺精细度和极限灵敏度的影响。最后,实验验证了谐振特性理论分析的正确性,并通过优化谐振腔参数实现陀螺零偏不稳定性0.059°/h,对谐振式光纤陀螺工程设计具有理论指导意义。

基于软玻璃光纤产生中红外超连续谱研究进展

随着软玻璃光纤的发展和光纤激光器的进步,越来越多的研究人员采用以软玻璃光纤代替石英光纤的方式,得到高功率中红外超连续谱光源。通过广泛阅读国内外关于氟化物玻璃光纤、硫系玻璃光纤和碲酸盐玻璃光纤等软玻璃光纤产生超连续谱的相关文献,本文综述了近年来利用这三类光纤产生中红外超连续谱光源的研究进展。目前氟化物玻璃光纤在实验中的应用最为广泛,且研发进度较快,获得的中红外超连续谱覆盖范围在2~5µm,最大输出功率可达30 W;硫系玻璃光纤产生的中红外超连续谱光源带宽可达10µm以上,但输出功率较低;碲酸盐玻璃光纤由于材料中羟基难以去除,在中红外超连续谱的实验中进展较为缓慢;而氟碲酸盐光纤在近几年发展迅速,可能成为未来中红外超连续谱研究的理想介质。

平顶型CLPG-CFBG级联结构中温度应力传感特性的研究

为了使光纤光栅传感器在光纤传感系统的应用中同时具有温度应力双参量传感和通信传输的功能,提出了一种由啁啾长周期光纤光栅(CLPG)和啁啾光纤布喇格光栅(CFBG)组成的平顶型光纤光栅传感器结构。采用测量中心波长位移的方法,建立了传感器温度和应力灵敏度系数矩阵,进行了理论分析和仿真验证。结果表明,CLPG的温度和应力灵敏度大小分别为2660 pm/℃和132 pm/με;CFBG的温度和应力灵敏度大小分别为12.6 pm/℃和0.8 pm/με,且CLPG和CFBG同时都具有平顶输出光谱,平顶光谱带宽分别达到了13.8 nm和5.6 nm,该传感器可以实现温度应力双参量同时传感,具有稳定的通信传输波段。该研究为光纤光栅传感器在光纤传感系统中的应用提供了参考。

高铁地震波场的高精度密集观测及应用前景:基于通讯光缆的观测和处理结果

利用高清分布式光纤声波传感(HD-DAS)系统,进行高铁地震波场的高精度分布式采集。传感单元采用结构简单、成本低廉的通信光缆即可实现很好的监测效果,可以方便地根据实际环境进行布设,大大提高了野外观测的效率。采用多光缆并行布放,信号叠加后可有效地抑制噪声,提高高铁地震信号的信噪比。对HD-DAS系统采集到的高铁地震信号进行数据分析,发现高铁地震信号呈现分立谱特性。通过分析地震波信号的衰减规律,并通过频率-波数谱得到地震波在近地表的传输速度,表明光纤采集的高铁地震波信号可用于探测地下结构,并进一步实现对介质状态变化的监测,从而保障高铁的运行安全。

光纤模式散斑对天文光纤光谱测量精度影响及其抑制方法

在利用多模光纤进行太阳表面磁场、视向速度测量等高分辨率天文光谱探测时,获得的光谱图像存在明显的能量分布不均匀的现象,出现了散斑。分析其原因可知,光纤光谱成像时,成像系统收到的是光纤出射端不同波长的像沿色散方向的展开。而光谱仪的高色散率使成像系统的每个像元所对应的光谱范围都非常窄,具有非常好的相干性。多模光纤内存在多种传输模式,每个波长的各个模式之间干涉形成的散斑图样的能量中心会偏离光纤几何中心,降低了光谱测量准确度。为了解决这一问题,设计了一种抑制散斑影响的多维机械扰模系统,用来提高光纤光谱测量精度。多维机械扰动装置由三个不同方向、不同频率运动的机械结构组成。通过调节三个机械装置以不同的频率振动,使光纤中的传导模式产生接近随机的相位漂移,从而使光纤出射端的散斑图样发生随机改变,经过长时间曝光(对应多幅散斑图样叠加平均)可以消除散斑的影响。为了检验系统的扰模效果,使用芯径为35μm的光纤研究了650 nm激光的出射散斑场能量分布,并提出以能量中心偏移位置的标准偏差作为光纤模式散斑能量分布离散度以及对天文光纤光谱测量精度影响的评价函数。首先,对比分析了不扰模、手动扰模、一维扰模和多维扰模下的各1000张散斑图叠加平均效果,结果显示手动扰模和多维机械扰模效果较好,散斑平均叠加图能量分布较为均匀。然后,又比较了散斑图叠加数量(等效于不同曝光时间)的多维扰模效果。实验结果表明,经过多维机械扰模的100张散斑图叠加平均后,标准偏差仅为单张散斑图的1/13。最后,对扰模装置频率和振幅对扰模效果的影响进行了测试。结果表明较高的频率和振幅都有益于散斑抑制。对于本次实验中光纤而言,频率选为1.2 Hz、振幅选为6 cm最为合适。在此条件下,散斑的平均质心偏移距离最小,为0.21个像素。