低弯曲损耗少模光纤传输特性研究

提出一种采用少模阶跃光纤与单模光纤连接的方法,实现低弯曲损耗传输的新型光纤通信系统。采用有限元法研究了在模场直径相同的情况下少模光纤纤芯半径与折射率差的关系,以及不同参数下光纤的弯曲损耗;采用光束传播法计算了少模光纤的各种模式与普通单模光纤的基模的连接损耗。证明了采用少模光纤可以利用模式间的正交性实现有效的单模传输,并具有低的弯曲损耗和连接损耗。     

一种基于三芯光纤的模式复用器/解复用器的设计

提出了一种基于三芯光纤的模式复用器/解复用器,三个纤芯包括两个相同的单模纤芯和一个少模纤芯,在少模纤芯中写入长周期光纤光栅以实现单模纤芯中LP01模与少模纤芯中LP11模间的转换。同时从两个单模纤芯输入LP01模,能激发少模纤芯中两个简并的LP11,a模和LP11,b模。采用光束传播法分析了该模式复用器/解复用器的耦合特性及串扰。数值模拟结果显示,若以少模纤芯中LP11模输出能量大于-1dB的波长范围作为该模式复用器/解复用器的工作带宽,则能够达到23nm,并且少模纤芯中生成的其他模式的输出能量皆比LP11模的输出能量小-21dB以上。该模式复用器/解复用器能够实现对少模光纤的模式复用与解复用,并具有极低的串扰。     

Research and analysis of Brillouin distributed sensing system based on quasi-single-mode few-mode fiber

A distributed fiber sensor was fabricated by splicing two single-mode fibers(SMFs) using the few-mode fiber(FMF) technique. A Brillouin optical time domain analysis(BOTDA) system was developed to measure the sensor’s temperature and bending performance. Two-mode and four-mode step FMFs were combined to splice the few-mode segment. The results indicate that the temperature response coefficients of the few-mode segment are only slightly higher than those of the connected single-mode segment, measu...     

少模光纤干涉仪性能的数值仿真研究

本文用数值仿真的方法研究了基于LP01模和LP02模干涉的少模光纤干涉仪的性能与光纤参数的关系.用有限差分法数值求解少模光纤干涉仪中单模光纤和少模光纤的导模.在少模光纤的LP03模截止且LP02导通的参数范围内,计算了调制深度和耦合效率与少模光纤参数的关系.计算结果表明,在采用SMF-28作为输入输出单模光纤的情况下,通过优化设计少模光纤的参数,可以使得调制深度大于98%,耦合效率接近于0.5.     

All-fiber sensor based on few-mode fiber offset splicing structure cascaded with long-period fiber grating for curvature and acoustic measurement

An all-fiber sensor based on a single-mode–few-mode–single-mode fiber offset splicing structure cascaded with long-period fiber grating is proposed and demonstrated for curvature and acoustic signal measurement. High-order mode is inspired in the few-mode fiber by the offset splicing structure and coupled into the LPFG, resulting in a splitting into two dips of LPFG attenuation band, which are more sensitive to the external environment change. The results of the curvature sensing experiment show that the intensity of the two resonant dips has a linear response to curvature in the range of 0.124–0.304 \({\hbox {m}}^{-1}\), and the sensitivity is about 93.01 \({\hbox {dB/m}}^{-1}\), which is one order of magnitude higher than congeneric curvature sensors demonstrated by other researchers before. Based on the curvature sensing mechanism, the sensor is also demonstrated for acoustic measurement in the range 110–230 Hz. The sensor shows a sensitivity of about 15 mV/Pa at 110 Hz and 4.5 mV/Pa at other frequencies. High sensitivity and easy fabrication make it a preferable candidate for curvature and acoustic sensing in the field of structural health monitoring.     

Theoretical and experimental analysis of thermal stress effects onmodal polarization properties of highly birefringent optical fibers

A theoretical and experimental analysis of thermal stress effects on the modal polarization properties of highly elliptical-core fibers is presented. The theoretical analysis is based on solving the vectorial Maxwell's equations, using a finite-element scheme, when form-induced and stress-induced effects are introduced simultaneously through appropriate calculation of the refractive indexes of the anisotropic media. The experimental analysis is done by studying the temperature response of a white-light interferometric sensor employing highly elliptical-core fibers. The calculated temperature sensitivities of the modal birefringence and the polarization mode dispersion in highly elliptical-core fiber are in close agreement with the experimental results. Interpretation of the results useful for designing white-light interferometric sensors composed of highly elliptical-core fibers is also given     

Single-polarization single-mode optical fibers

Strictly speaking, an ordinary axially symmetrical single-mode fiber is a "two-mode" fiber because two orthogonally polarized HE11modes can be propagated in it. This fact results in the instability of the polarization state of the propagated mode when geometrical perturbation exists in the fiber, and also the so-called polarization mode dispersion. These are harmful in some applications of single-mode fibers to communication and measurement. To prevent these adverse effects, single-polarization single-mode (SPSM) optical fibers have been developed. Three basic types of the SPSM fiber are elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber. This paper describes the principles of these three types, performance obtained experimentally, theoretical approaches, and measurement techniques related to the SPSM fibers. Finally, relevant technical tasks in the future are mentioned.     

LP01 to LP11 mode convertor based on side-polished small-core single-mode fiber

An all-fiber LP01-LP11 mode convertor based on side-polished small-core single-mode fibers (SMFs) is numerically demonstrated. The linearly polarized incident beam in one arm experiences π shift through a fiber half waveplate, and the side-polished parts merge into an equivalent twin-core fiber (TCF) which spatially shapes the incident LP01 modes to the LP11 mode supported by the step-index few-mode fiber (FMF). Optimum conditions for the highest conversion efficiency are investigated using the beam propagation method (BPM) with an approximate efficiency as high as 96.7%. The proposed scheme can operate within a wide wavelength range from 1.3 μm to1.7 μm with overall conversion efficiency greater than 95%. The effective mode area and coupling loss are also characterized in detail by finite element method (FEM).     

激光切割板材的工艺处理

本文在现有的激光切割工艺研究的基础上对激光切割板材的工艺处理进行了进一步的探讨 ,其中包括引入线、引出线的设置 ,辅助切割路径的合理安排 ,路径优化和优化排样以及加工参数的优选等等 ,结合计算机的应用 ,实现计算机辅助工艺设计 (CAPP)。     

Miniature fiber Fabry-Perot sensors based on fusion splicing

Fiber-optic Fabry-Perot (F-P) sensors are widely investigated because they have several advantages over conventional sensors, such as immunity to electromagnetic interference, ability to operate under bad environments, high sensitivity and the potential for multiplexing. A new method to fabricate micro-cavity Fabry-Perot interferometer is introduced, which is fusion splicing a section of conventional single-mode fiber (SMF) and a section of hollow core or solid core photonic crystal fiber (PCF) together to form a micro-cavity at the splice joint. The technology of fusion splicing is discussed, and two miniature optical fiber sensors based on Fabry-Perot interference using fusion splicing are presented. The two sensors are completely made of fused silica, and have good high-temperature capability.     

Modal cutoffs in single- and few-mode fiber couplers

Optical coupling, or crosstalk, between two parallel, identical single- or few-mode fibers is describable as a superposition of the modes of the composite waveguide. Like the modes of a single-fiber waveguide, the modes of the two-fiber waveguide are cut off. Exact and simple accurate asymptotic formulae are derived giving the cutoff value as a function of separation. For single-mode couplers, perturbation theory gives the fundamental and second modesPsi+andPsi-as the sum and difference of the fundamental modesPsi_{1}andPsi_{2}of each fiber. In realityPsi+is the fundamental mode of the composite waveguide, whereasPsi-is the second mode and has a finite cutoff. This limits the smallestV-value for which low-loss coupling is possible. The limitation is least severe for step-profile fibers.     

Birefringence calculations in elliptical-core optical fibres

It is shown that in the useful single-mode region, the birefringence properties of elliptical-core fibres match very well with those of a rectangular-core waveguide having the same core area, same aspect ratio and same core and cladding refractive indices. This gives a simple method of obtaining the birefringence and V-value for maximum birefringence in ellipticalcore fibres.     

光纤电流传感器

单模光纤电流传感器在不断克服线双折射对 Faraday 效应的干扰中发展;多模光纤电流传感器具有可靠稳定的特性,容易实现实用化。     

抗恶劣环境的保偏光纤温度传感器

基于应力型保偏光纤传输常数差对温度的敏感性并利用偏光干涉技术,提出了一种反射型保偏光纤温度传感器并推导出传感方程。在传感器中采用宽谱光源抑制了输入/输出光纤中偏振耦合引起的误差,特性分析表明这种传感器实用、精度高并且配置灵活。实验结果与理论完全吻合,其噪声等效可探测温度精度达0.01℃。根据大型电力变压器的绕组温度监测要求,研制出一套远程多路温度传感器系统。采用特殊的涂覆和密封石英毛细管封装技术,保证光纤传感头能在热油及250℃的高温下工作,而且具有很高的绝缘性。检测结果表明传感器在0~200℃内,达到了±0.5℃测量精度。     

Bragg grating-based laser sensors systems with interferometricinterrogation and wavelength division multiplexing

We describe the use of fiber Bragg grating based lasers as sensors. An interferometric detection technique is presented for interrogating laser wavelength shifts due to measurand induced laser cavity strain with high resolution from both single-mode and multimode lasers. The principle of integrating multiple sensors to form an array is demonstrated using a wavelength division multiplexing approach     

Interféromètres modaux à symétrie circulate dans les fibres optiques

The spectral response of a few-mode fiber in the case of LP₀₁/LP₀₂ excitation is studied showing the similarities and differences between the transmission of such a bimodal interferometer and that of a classical interferometer. The applications envisaged are, on the one hand, the characterization of fibers (in particular by measurement of an equalization wavelength), and on the other hand, the development of all-fiber interferometric sensors without the need of a separate reference arm.     

基于少模光纤布拉格光栅的模分复用系统实验研究

本文提出了一种基于少模光纤布拉格光栅(Few-mode FBG)的模分复用通信系统,阐述了基于少模光纤布拉格光栅的模分复用/解复用原理,建立了2×2的模分复用实验系统,分别利用LP01和LP11模作为独立信道,实现了1.25 Gbps和622Mbps两路伪随机序列(PRBS)的10km传输实验,给出了传输后的眼图,分析了当激光器波长为1549.228nm时,实验系统的误码特性.实验验证了基于少模光纤布拉格光栅的模分复用通信系统的可行性,为进一步实现长距离高速率的模分复用通信奠定了实验基础.     

Conditions for obtaining zero polarisation mode dispersion in elliptical-core fibres

It is shown that zero polarisation mode dispersion can never be achieved in elliptical-core single-mode fibres by geometrical birefringence alone. To equalise the group delays of the two fundamental modes, stress-induced birefringence must be introduced to cancel, partly or completely, the geometrical birefringence, depending on the application.     

Elliptical-core, two-mode optical fibre sensors as vibration-mode filters

Reggedised two-mode elliptical-core fibre sensors are shown to be selective in sensing the different modal frequencies of vibration from a clamped-clamped beam. Sensor placement on a flexible structure is shown to be critical in the design of fibre sensors that measure an integral of strain over their entire sensing lengths. Experimental results confirm theoretical predictions and efficient vibration-mode selectivity is demonstrated.<>     

一种高灵敏度相位调制单模光纤传感器的信号处理系统

报道一种高灵敏度相位调制单模光纤传感器的信号处理系统。简述了系统的传感原理,讨论了辨向检测电路和信号的计算机处理。