光纤损耗对皮秒脉冲孤子效应压缩的影响

在计及常规光纤损耗的前提下，通过数值求解求解修正的非线性薛定谔方程，全面地计算和分析了损耗对皮秒脉冲在单模光纤中孤子效应压缩过程的影响。结果表明，与不计及损耗时相比，损耗一方面导致脉冲压缩比，压缩后的脉冲峰值功率和脉冲压缩质量的下降，另一方面还导致所选用的最佳光纤度的增加。进一步研究表明，损耗对脉冲压缩的影响程度还与输入脉冲的峰值功率和脉宽有关。     

掺钕光纤放大器的弯曲损耗对增益的影响

利用掺钕光纤放大器的粒子数速率方程、功率传输方程和光纤弯曲损耗公式,对光纤弯曲损耗所引起的增益变化进行了数值模拟,分析了对于不同半径和波长下光纤弯曲损耗对光纤增益的影响,结果表明,对于一定长度的光纤,其增益随弯曲半径的减小而减小,当弯曲达到一定值时,增益发生急剧的降低;随弯曲半径的减小,其增益谱线发生下移,这对实验研究有着重要的指导意义。     

光纤弯曲损耗特性的理论与实验研究

为了减小在长距离光纤通信中存在的弯曲损耗和利用光纤激光器中的弯曲损耗获得单模输出，利用速度法解释了光纤弯曲损耗机制，采用Marcuse理论研究了弯曲损耗随弯曲半径、波长和纤芯半径变化的关系。通过计算机仿真和实验得出弯曲损耗随弯曲半径的减小而增大，随波长的增大而增大，随纤芯半径的增大而增大，高阶模式的损耗大于低阶模式。利用这一结论就可以通过控制弯曲半径在临界半径以内来减小通信中的弯曲损耗，通过增大模场半径来实现光纤激光器中的单模输出。     

Lensless intracavity focusing in a passively Q-switched all-fiber laser using the mode-field-area mismatch

Intense lensless intracavity focusing in a saturable absorber Q-switched all-fiber laser resonator by use of loss arrangement and mode-field-area mismatch between the fibers is investigated for the first time. The intracavity power distribution was related to the locations and values of the cavity losses as the saturable absorption loss, the reflection loss of the output coupler, and the splicing loss between the gain fiber and the absorber fiber. With a mode-field-area mismatch and a reduced splicing loss with the gain fiber, a power density in the absorber fiber was achieved that was 11.9 times higher than that in the gain fiber.     

单模与多模光纤耦合器的光束合波

现有的光纤耦合器在作为分波器使用时具有较低的插入损耗,在作为合波器时插入损耗较大,为实现低损耗合波目的,提出一种由单模与多模光纤共同构成的混合型光纤耦合器。利用耦合波方程理论分析其工作原理,计算机模拟其耦合过程。采用熔锥法制作工艺,完成单模与多模光纤耦合器的制作,实验结果与理论模拟相吻合;该器件单模到多模光纤的耦合效率、多模到多模光纤的耦合效率均在90％以上,实现了两路光束的功率合波。作为低插入损耗合波器件可广泛应用于光通信以及双包层光纤激光器抽运光的注入。     

新型抗弯曲大模场面积光子晶体光纤

研制出一种新型抗弯曲大模场面积石英光子晶体光纤. 利用光子晶体光纤结构设计的灵活性, 通过规划缺陷的位置及空气孔的尺寸, 实现了大模场面积单模及低弯曲损耗特性.应用建立的实际光子晶体光纤特性分析模型, 研究了研制光纤的模式特性和弯曲特性, 在波长1064 nm处, 平直状态下光纤的模场面积可以达到2812 μm², 基模限制损耗为0.00024 dB/m, 高阶模限制损耗高于1.248 dB/m. 基模和高阶模之间的高传输损耗差, 保证了在获得大模场面积的同时实现单模传输. 弯曲半径和弯曲方向角所带来弯曲损耗变化的研究结果显示, 即使在弯曲半径小到5 cm时, 弯曲损耗也在10^-3 dB/m量级以下, 而且在弯曲半径为30 cm时光纤可承受的弯曲方向角范围扩展至-60°–60°. 研制的光纤具有良好的低弯曲损耗特性, 可有效解决非对称结构所带来的光纤弯曲特性对弯曲方向角敏感的问题. 该光纤在高功率光纤激光器、放大器及高功率传输等技术领域具有重要的应用价值. 关键词： 光子晶体光纤 大模场面积 低弯曲损耗 弯曲方向角     

双面曝光长周期光纤光栅偏振相关损耗

研究了采用高频CO2激光脉冲通过单面和双面曝光制作出的长周期光纤光栅(LPFG)的偏振相关损耗特性。单面曝光制作的长周期光纤光栅由于光纤横截面折射率改变不均匀,对入射光偏振态有较强的依赖性,主要表现为偏振相关损耗较大;为了降低偏振相关损耗,在制作长周期光纤光栅的过程中采用双面曝光的方法,以使其横截面折射率调制受高频CO2激光曝光改变均匀。实验数据显示,高频CO2激光脉冲制作的普通单面曝光长周期光纤光栅最大偏振相关损耗高达1.24 dB,而采用双面曝光的相同谐振峰值长周期光纤光栅的偏振相关损耗则可降至0.42 dB。因此,双面曝光制作的长周期光纤光栅能较好地克服入射光偏振态的不良影响,从而满足对偏振敏感的光纤通信和传感系统的应用要求。     

Wavelength-dependent selective loss for wavelength switching operation of an erbium-doped fiber ring laser

A wavelength-switchable erbium-doped fiber ring laser based on a wavelength-dependent selective loss fiber filter is demonstrated and reported. The filter is based on a long-period fiber grating and bending loss. The operating wavelength of the fiber laser can be switched from a single-wavelength operation at 1565 to 1527 nm.     

氟锆酸盐玻璃光纤的研制

本文介绍聚全氟乙丙烯包皮的氟锆酸盐(ZrF_4-BaF_2-LaF_3-AlF_3-NaF)玻璃光纤的制备方法.研究了各种工艺因素对氟锆酸盐玻璃和光纤散射损耗的影响.结果表明,选择适当的熔化温度和均化时间,玻璃熔化和光纤拉制时环境中低的水含量是制得的损耗氟锆酸盐玻璃光纤的关键;配合料中引入适量NH_4HF_2,选用温度结构合理的拉丝炉及拉丝工艺也有助于降低光纤的损耗.在此工作基础上,获得了波长2.32μm处损耗为0.24dB/m的氟锆酸盐玻璃光纤.     

偏芯光纤弯曲特性分析

根据光纤传输理论建立了偏芯光纤理论计算模型.采用保角变换方法将偏芯光纤不对称的三层结构转换成同轴对称的三层结构,得到关于传播常量的特征方程,给出了偏芯光纤弯曲损耗公式.仿真分析了偏芯光纤弯曲损耗和弯曲半径之间的关系,结果表明当弯曲半径达到3mm时,弯曲损耗几乎为零,同时得到弯曲损耗随偏芯距离的变化关系.运用Rsoft软件中的BeamPROP模块建立偏芯光纤弯曲的光学模型,模拟仿真了弯曲的偏芯光纤中模场分布情况.仿真结果表明,偏芯光纤的弯曲方向与纤芯偏移中心轴线方向相同的弯曲损耗小于反方向的弯曲损耗.     

Periodic bending loss in multimode W-type fiber

Additional loss in a W-type fiber induced by periodic bends is investigated experimentally in comparison with the corresponding singly clad (SC_p and SC_q) fibers. When the bending amplitude is small, the additional loss of the W-type fiber is almost equal to that of SC_p fiber. However, as the amplitude becomes larger, the loss increases and gradually approaches the value for SC_q fiber.     

Design of sidetap fiber Bragg grating filters

A comprehensive theoretical treatment is presented for bound-mode to radiation mode coupling loss (transmission loss) and for bound-mode to bound-mode Bragg reflection (back reflection) in a sidetap fiber phase grating. The spectra of the reflection and transmission loss in a tilt angle range useful for fiber sidetap filter design is presented for the first time. Important dependencies between the designed wavelength of operation and parameters of the fiber grating, which give a clear understanding of the process of the fiber mode to radiation mode coupling and back reflection is also discussed. A practical procedure for the design of sidetap gain flattening filter is also presented.     

小芯径掺铒光纤与单模光纤低损耗接续的研究

报道了掺铒光纤放大器中降低掺铒光纤与单模光纤接续损耗的一种新方法，采用在芯区直径较小的掺铒光纤端部拉锥的方法，使得掺铒光纤中的传输模场在锥形区域内扩散，从而与单模光纤中直径较大的本征模场良好匹配，实现低损耗接续，初步实验结果表明，该方法可获得小于１ｄＢ的接续损耗。     

2.5THz环烯烃聚合物中空芯光子晶体光纤设计与实验

采用全矢量有限元法,仿真设计了一种工作在2.5THz频段的中空芯太赫兹光子晶体光纤,用环烯烃聚合物材料(COC)制备了光纤样品,利用CO2激光泵浦气体太赫兹源搭建了测试平台并对光纤的太赫兹波传输性能进行了测试。实测光纤最低损耗0.17dB/cm、平均损耗约0.5dB/cm,在弯曲90°情况下光纤传输损耗波动小于5%,具有良好的可弯曲性;光纤输出端口的模场分布测试结果表明,光纤是以主模进行传输,太赫兹能量很好地被束缚在光纤芯中。     

Influence of the UV-induced fiber loss on the distributed feedback fiber lasers

It was found that the output power of the distributed feedback fiber lasers would be improved after annealing or left unused for several days after the laser had been fabricated, and the output of the fundamental mode would not increase but be clamped while the ±1 order modes would be predominant with the enhancement of the coupling coefficient during the fabrication. The paper discussed the influence of UV-induced fiber loss on the fiber phase-shifted DFB lasers. Due to the gain saturation and fiber internal loss, which included the temperament loss and permanent loss, there was an optimum coupling coefficient for the DFB fiber lasers that the higher internal fiber loss corresponded to the lower optimum values of coupling coefficient.     

Experimental investigation of an inhomogeneous loss and its influence on multiwavelength fiber lasers

Inhomogeneous loss generated by multimode laser linewidth broadening in an optical fiber is experimentally studied. With this mechanism, multiwavelength lasing is achieved by use of either fiber Raman gain or erbium-doped fiber gain. Through various pump powers and optical filter bandwidths, the relationship between inhomogeneous loss and the performance of a multiwavelength fiber laser is studied, and a physical explanation is provided.     

飞秒激光刻蚀非平行壁光纤微腔Mach-Zehnder干涉仪特性及其流体传感研究

实验发现,飞秒激光微加工光纤微腔时,两个侧壁与纤芯轴向并不完全垂直, 刻蚀的非平行壁光纤微腔Mach-Zehnder干涉仪出现光程差随波长增大而线性减小、 微腔总损耗随波长增大呈递减变化等反常现象.对此,提出非平行壁光纤微腔Mach-Zehnder 干涉仪新模型并初步建立了分析理论,采用新模型及分析理论对新型微腔干涉仪特性进行了研究. 数值分析了微腔底角、深度等参数对谱峰波长位置的影响,理论研究了微腔的光波传输损耗、 吸收损耗、插入损耗、材料红外吸收损耗以及对干涉条纹对比度的影响, 理论分析与实验结果相符.实验获得水溶液干涉条纹对比度高达35 dB的非平行壁光纤微腔Mach-Zehnder干涉仪, 将新型光纤微腔干涉仪用于流体传感,其蔗糖水溶液折射率传感灵敏度高达-12937.31 nm/RIU.     

光纤数据链路模拟器设计

为分析光纤制导导弹飞行中光纤信道变化情况,满足导弹动静态仿真需求,设计了一种能够模拟光纤数据链路传输损耗特性的装置。研究内容包括建立系统传输损耗的动态、静态模型。利用光模拟器实现导弹飞行中可能遇到的信道干扰、数据延迟、动态损耗等情况。实验结果表明,光信号干扰的变化范围达到-50 dBm～-40 dBm,光信号的传输延迟范围为16.65 s～99.9 s,模拟器动态损耗调整范围为0 dBm～50 dBm,可用于验证导弹光纤传输系统的性能。     

大芯径空气包层微结构光纤实现kW级激光传输

kW级高功率激光柔性传输是激光清洗、激光焊接、激光刻蚀等高功率激光加工领域中必备的环节,而实现高功率激光低损耗传输的光纤是其关键器件。目前高功率激光传输光纤采用大芯径传能光纤,仍然存在着弯曲损耗大、柔性差等问题,并且使用过程中要经常维护。华南师范大学特种光纤研究中心提出一种大芯径空气包层微结构光纤,利用包层的空气孔可以极大降低激光泄露的风险,降低光纤制备过程中对耐高温涂敷层的严苛要求,实验结果证实该光纤在室温无制冷条件下可实现kW级激光传输,从而为10 kW级高功率激光柔性传输奠定基础。     

A 168-km ultra-long-range OTDR measurement at a wavelength of 1.55 μm

A Rayleigh backscattered signal and Fresnel reflection over a 167.6-km and a 251.2-km long pure silica-core fiber (PSF) with fiber loss 0.176 dB/km, and a 138.6-km and a 206.5-km long Ge-doped core dispersion shifted fiber (DSF) with fiber loss 0.218 dB/km have been observed with ultra-long-range optical time domain reflectometry (OTDR) using a 1.55-μm high-power semiconductor laser (LD) and InGaAs-APD with a low dark current at room temperature. The Rayleigh backscattered signal level and fiber loss are strongly dependent on the fiber dopant materials and fiber structural parameters. DSF gives a better SNR for short length fibers because the Rayleigh backscattered signal level is larger than PSF, but because the DSF loss is also larger, PSF gives a better SNR for fibers longer than the critical length. Accordingly, the dynamic range of OTDR in the different fiber types such as PSF and DSF becomes different. One-way backscattered dynamic ranges of 29.5 dB for the PSF and about 30.2 dB for the DSF at room temperature have been achieved.