Analysis of shupe effect in polarization-maintaining photonic crystal fiber-optic gyroscope

The Shupe effect in a fiber optical gyroscope with polarization-maintaining photonic crystal fiber was studied. The thermal sensitivitise of the polarization-maintaining photonic crystal fiber and conventional polarization-maintaining fiber were simulated and measured. Then the Shupe error in the gyroscope was analyzed. The contrast results showed that the Shupe error of the gyroscope with the polarization-maintaining photonic crystal fiber is quantitatively comparable to that using the conventional polarization-maintaining fiber.     

Bending insensitivity of fiber Bragg gratings in suspended-core optical fibers

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0.14 dB bending loss at a bending radius of 6.35 mm.     

Differential birefringence in Bragg gratings in multicore fiber under transverse stress

We present experimental measurements of the peak splitting of the reflection spectra of fiber Bragg gratings as a result of birefringence induced by transverse loading of a multicore fiber. Measurements show that the splitting is a function of the applied load and the direction of the load relative to the azimuth of the fiber. A model for calculating the stress in the fiber that is due to an applied load is in good agreement with our experimental observations.     

微磨削斜面光纤透镜平面度试验研究

为了研究微磨削参数对斜面光纤透镜平面度的影响,减小微磨削方法加工斜面光纤透镜的平面度误差,采用正交试验法对直径Ф125 μm单模光纤的30°斜面光纤透镜的微磨削进行了试验。结合微磨削的磨削力模型和材料力学弹性梁变形理论, 分析微磨削过程中随着磨削用量的变化所导致的光纤透镜被磨削斜面的平面度的变化规律。理论分析和实验结果表明:光纤悬伸长度对斜面光纤透镜平面度的影响最大,增大光纤悬伸长度将导致较大的斜面光纤透镜平面度的轮廓误差,恰当的磨削用量组合能够获得较小的平面轮廓误差。通过试验磨削出了平面度误差为3 μm的30°斜面光纤透镜。     

锥形光纤模场直径极小值特征研究

模场直径是光纤波导基模的特征参量。单模光纤中的功率密度与模场直径成反比。随着光纤激光器单模输出功率的不断攀升,纤芯中的功率密度不断增加,过高的功率密度会使光纤波导产生光学损伤和热损伤。基于锥形光纤模场分布近似模型,研究发现不同参数的拉锥光纤模场直径最小值位置对应的归一化频点具有规律性。采用有限差分波束传播法（FD-BPM）对不同波长、不同数值孔径下纤芯直径和模场直径的对应关系进行模拟,结果表明:模场直径最小值位置在归一化频率1.8附近,与光纤参数和波长的选取没有直接关系。这个特征参数可为高功率激光在光纤中功率密度最大值位置的快速确定提供依据,也为光纤光学理论增加了新的内涵。     

光子晶体光纤布拉格光栅传输谱特性的分析

研究光子晶体光纤中光纤光栅的传输谱特性对于研制基于光子晶体光纤的光纤光栅器件有着重要的意义。结合耦合模理论和光束传输相关函数方法,对一种典型光子晶体光纤中的布拉格光栅(FBG)传输谱进行了理论分析。比较了光子晶体光纤中布拉格光栅与常规布拉格光栅的传输谱。数值分析了光纤截面结构变化对于光栅传输谱的影响,并给出这种影响的定性解释。计算结果显示,与常规光纤光栅相比,包层模共振引起的损耗峰与正反向纤芯模耦合引起的损耗峰可以相比拟,而包层模共振的间隔也比常规光纤中光纤光栅的包层模共振间隔要大。同时给出了晶体光纤截面上空气孔的占空比,空气孔的排布层数对于传输谱影响的规律。     

Synchronization of optical polarization conversion and scattering in chiral fibers

We demonstrate that polarization transformation and scattering in adiabatically twisted single-mode birefringent optical fibers is synchronized so that light in one evolving elliptically polarized mode is freely transmitted while orthogonally polarized light is scattered out of the fiber. Thus, linearly polarized radiation initially oriented along the fast axis of the untwisted fiber is transformed to circularly polarized light with the same sense of rotation as the twisted fiber and is scattered out of the fiber. When the fiber twist is first accelerated and then decelerated, the fiber becomes a broadband, low-insertion-loss, linear polarizer.     

基于少模光纤的SBS光谱阈值特性分析

受激布里渊散射会影响少模光纤传输系统中的信噪比、传输距离与传输容量,是影响传输系统入纤功率提高的重要因素。对阶跃型少模光纤的受激布里渊散射谱的阈值进行了研究,运用了布里渊散射谱、模式联运谱的数学模型对少模光纤散射特性进行了分析,探讨了少模光纤布里渊散射增益谱、阈值增益系数,以及光纤各参量对少模光纤阈值的影响。分析结果表明：SI-10阶跃型少模光纤中存在五种不同的传播模式,不同模式有各自的传输常数以及有效折射率,各模式相互作用导致模式展宽、增益降低,且布里渊散射谱峰值增益系数为3.9×10-11 m·W-1。阈值增益系数受到光纤传感距离的影响,在相对较短距离传输中阈值急速下降,且其趋势随长度增加渐趋平缓,当光纤长度达到22 km时阈值增益系数趋于常数18.1。少模光纤的阈值因光纤长度的递增而递减,且递减趋势渐缓趋于常数20.5 dBm;少模光纤不同模式受激布里渊散射的阈值也因光纤长度的递增而递减最终趋于常数,且不同模式的阈值因模式阶数的递增而递增;少模光纤的阈值随着光纤衰减系数和纤芯半径的递增而递增,且增加趋势缓慢增大。不同衰减系数的光纤其阈值在不同长度趋于常数,衰减系数越大受激布里渊散射阈值越大越容易趋于一常数。     

磁光非线性光纤中光参量增益的研究

将光纤中磁光效应和非线性效应作为微扰,推导了磁光四波混频的耦合模方程.通过解析解研究了各向同性磁光非线性光纤的参量过程,并指出利用磁光耦合系数的色散特性可以实现四波混频的相位匹配.同时,采用龙格-库塔法分析了在线双折射磁光非线性光纤中,忽略费尔德常量的波长依赖性时,左旋圆偏振光参量增益的磁控特性,指出了实验中采用较高费尔德常量的非线性光纤的必要性.研究表明:1)对于低线双折射磁光非线性光纤,优化双折射大小可以获得最大的参量增益;2)根据参量增益对磁光耦合系数的单调依赖特性,适当选择光纤长度、泵浦功率以及输入导波光的偏振态,可使参量增益的磁可调范围大大提高.     

大功率激光单模光纤远距离传输的注入光纤光功率限值分析

对于大功率激光单模光纤远距离传输, 采用传统的受激拉曼散射(SRS)阈值作为注入光纤激光功率值取值过大。本文对单模光纤远距离传输过程中泵浦光和拉曼斯托克斯光(Stokes)光功率随注入光纤激光功率的变化进行仿真与理论分析。根据光纤中SRS产生的机理, 提出以拉曼Stokes光在单模光纤中传输的光功率变化曲线曲率极大值点对应的注入激光功率为限值, 对注入单模光纤光功率限值随着光纤长度变化进行仿真, 通过曲线拟合得出注入单模光纤激光功率限值公式, 并搭建实验系统进行验证。结果表明, 提出的注入单模光纤激光功率限值适用于大功率激光远距离单模光纤传输。     

Investigation of a coated optical fiber strain sensor embedded in a linear strain matrix material

A theoretical model has been developed to study the mechanical behaviors of the interface between an embedded optical fiber with coating material and a linear strain matrix. The results show that the longitudinal stress and strain in the fiber optic sensor are different from that distributed in the host material and depend on the strain distribution and embedded length of the optical fiber as well as the material properties of the fiber coating. The distribution of interfacial shear strain between the coating and the glass fiber and the distribution of strain/stress of the glass fiber are given.     

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。     

侧面抛磨极化光纤的传输特性分析

针对侧面抛磨极化光纤的物理结构，提出了极化光纤的双金属包覆六层波导模型，并对其传输特性进行了分析。分析指出，由于金属电极镀在极化光纤的侧面抛磨平面上，极化光纤中传播的光具有偏振消光特性。对极化光纤的传输特性影响较大的器件结构参量为被抛磨侧面与纤芯的距离，以及紧邻阳极的绝缘胶厚度。     

Role of weak interface to retain high strength of fiber in monofilamentary SiC fiber/titanium-aluminide composite

The tensile strength of monofilamentary weakly bonded SiC fiber/γ-TiAl intermetallic compound matrix composite, prepared by the sputtering method, was measured and analysed using a fracture mechanical technique. The main results are summarized as follows: (1) The fracture of TiAl occurred prior to that of fiber, resulting in formation of circumferential cracks on the fiber. Interfacial debonding occurred during tensile test, resulting in long pull-out of the fiber. (2) The strength of the fiber in the TiAl matrix was nearly the same as that of the bare fiber. (3) The fracture mechanical analysis showed that (i) the interfacial debonding grows unstably upon initiation and (ii) the stress distribution in the fiber in the cross-section, where the matrix is fractured, approaches to that of bare fiber with increasing debonded length. The reason why the fiber strength was maintained in spite of the formation of cracks on the fiber surface due to the premature fracture of the matrix was accounted for by the fully blunted crack-tip from the above calculation result.     

宽带放大器用碲基掺铒光纤结构参量的设计考虑

利用光波导理论及均匀展宽四能级模型，研究了宽带放大器用阶跃型折射率分布碲基掺铒光纤的结构参量—纤芯半径和相对折射率差的设计考虑.理论研究表明，在单模传输条件下，为获取最大信号增益，宜选择相对折射率差大的碲基掺铒光纤来构建光纤放大器.相对折射率差一定的情况下，在高泵浦功率、小信号输入或光纤长度短于各信道最佳增益长度时，选择纤芯半径大的碲基掺铒光纤可以得到大的信号增益；反之，宜选择纤芯半径小的碲基掺铒光纤.     

非均匀微结构光纤中双折射现象的研究

报道了利用飞秒脉冲激光与非均匀微结构光纤相互作用中产生超连续光谱后在非均匀微结构光纤传输中双折射拍频现象的研究.利用35?fs的飞秒激光脉冲在高双折射微结构光纤中的传输过程中直接观察到了拍频现象.并利用有限元方法对该光纤进行了模拟计算分析，计算得出在600?nm处拍频长度为毫米量级.所得结果与实验一致. 关键词： 双折射效应 微结构光纤 超连续光谱 有限元法     

Modeling the evolution of spatial beam parameters in parabolic index fibers

We analyze the evolution of beam quality when propagating through a parabolic index (PI) fiber. The deterioration in beam quality is expressed in terms of the fiber parameters, and a methodology for minimizing the deterioration is presented. The fiber optimization procedure is evaluated numerically for an application where the PI fiber is used to deliver the signal produced by a tapered fiber-bundle beam combiner. It was demonstrated that delivery with no beam quality deterioration can be achieved with proper fiber design.     

Effects of twisting and bending on LP21 mode propagation in optical fiber

Twisting and bending characteristics of low-multimode LP21 mode propagation in optical fibers is presented for the first time. Theoretical fiber mode modeling, combining geometrical rotation with opto-elastic effects, demonstrates that the propagation of the LP21 mode is bending-effect-immune. Experimental testing verifies that the LP21 mode specklegram rotates 0.9112 of the fiber twist angle in a fused silica fiber, independent of any fiber bending. This characteristic allows for the LP21 mode to be highly applicable in fiber specklegram sensors.     

Theoretical study of stimulated Raman scattering in long tapered fiber amplifier

A model that is based on the propagation equation and coupled mode theory is introduced in order to describe stimulated Raman scattering(SRS) effects in long tapered fiber amplifiers.Based on the presented model,fiber amplifiers with uniform and long tapered fibers are theoretically and numerically simulated.It can be drawn from the results of our simulations that the long tapered fiber has the advantage in suppressing SRS when applied in fiber laser amplifiers.Our results can provide guidance in the designing of system configuration in long tapered-fiber-based fiber laser systems.     

微流芯片中消逝波激励的荧光辐射特性研究

将石英裸光纤植入聚二甲基硅氧烷基片的微流道中,采用沿光纤轴向光抽运、消逝场激励染料分子的方式,在基片微流道中获得均匀的荧光辐射.实验发现,荧光辐射的强度随光纤轴向距离的增加而衰减,光纤包层溶液折射率越大,荧光沿光纤轴向的衰减越突出;包层溶液中染料浓度越大,荧光沿光纤轴向的衰减也越突出;通过选择适当的包层溶液折射率以及染料浓度可以获得沿光纤轴向接近均匀的荧光辐射.用消逝波激励荧光的辐射理论计算了荧光光强沿光纤轴向的变化,计算结果与实验符合较好.在此基础上,设计并制作了一种具有三个通道的聚二甲基硅氧烷基片,通过在三个微流道中分别注入染料浓度均为0.1 mmol的罗丹明640、罗丹明B及罗丹明6 G的乙醇染料溶液,采用沿光纤轴向消逝波光激励方式,在一块聚二甲基硅氧烷基片上同时实现了三个不同波段的荧光辐射.