熔锥型保偏光纤耦合器分光比的依赖性研究

基于耦合模理论,推导了熔锥型保偏光纤耦合器快慢轴耦合系数的关系式。通过对标准3 dB保偏光纤耦合器的偏振依赖性、波长依赖性、温度依赖性、双折射依赖性所引起的分光比变化的分析,得出了不同依赖因素对标准3 dB耦合器分光比稳定性影响程度的大小。分析结果表明,保偏光纤耦合器的双折射依赖性十分显著;波长依赖性和温度依赖性其次;在一定的工艺条件下,偏振依赖性可以忽略。另外,耦合器的固有双折射越大,分光比波动越大。所得结论对制作熔锥型保偏光纤耦合器的光纤选择、拉制工艺、封装工艺的优化和改进有重要意义。     

一种Sagnac干涉仪结构的光子晶体光纤温度传感器

采用Sagnac干涉仪结构,设计了一种高双折射光子晶体光纤环镜温度传感器。光子晶体光纤温度稳定性好,通过向高双折射光子晶体光纤空气孔填充热光系数高的液体材料乙醇,从而实现温度传感的目的。采用平面波展开法,分析了高双折射光子晶体光纤的双折射与传输波长和温度的关系。理论分析表明,填充乙醇后,高双折射光子晶体光纤的双折射随着传输波长和温度的增加而增加,且双折射与温度成线性关系。实验中将一段填充乙醇的高双折射光子晶体光纤与3 dB耦合器熔接制作成Sagnac干涉仪结构的光纤环镜,当温度从 45 ℃升至80 ℃时,光谱仪上观察到凹点λi向短波方向漂移了309.280 nm,温度灵敏度高达8.837 nm/℃。     

Polarization Characteristics of Single-Mode Fiber Couplers

The polarization characteristics of fiber couplers made of birefringent single-mode fibers are studied. The effect of anisotropic interfiber coupling, fiber birefringence, angular misalignment of fibers, and twisting on the coupler characteristics are identified. The polarization characteristics of the couplers are compared with that of isolated uncoupled fibers of the same birefringence and length. The equivalent lumped element representations for three classes of fiber couplers are also presented.     

Tunable optical filters using compound ring resonators for DWDM

The device is based on a loop mirror in a ring resonator. The loop mirror allows tuning by changing the coupling coefficient of a directional coupler. The loop mirror is implemented using a Sagnac configuration to have the same optical path between the signals to be interfered (copropagating and counterpropagating ones). The filter structure allows optical integration for having higher free-spectral ranges. Simple design equations for the filter parameters and the tuning are reported. Measurements on a passive optical fiber tunable filter are presented. There is a good agreement between measurements and theory.     

A standard fiber-based loop mirror as a gain-flattening filter for erbium-doped fiber amplifiers

We report flattening of the amplified spontaneous emission (ASE) spectrum from an erbium-doped fiber (EDF) using a standard fiber-based loop mirror (FLM), realized with an "over-coupled" fiber coupler. Through simulation, a bend-induced birefringent FLM as a gain-flattening filter is designed. Subsequently, an over-coupled coupler with a free spectral range of 140 nm is fabricated to realize the FLM, which is integrated to an EDF that is pumped by a 980-nm laser diode. By introducing an appropriate amount of bend-induced birefringence in the loop, the ASE spectrum of the EDF could be flattened within /spl plusmn/0.5 dB over a wavelength range of 32 nm in the C-band.     

Nonlinear propagation and self-switching of ultrashort opticalpulses in fiber nonlinear directional couplers: the normal dispersionregime

The propagation of short optical pulses in a nonlinear directional coupler operating in the normal dispersion regime is investigated. The specific example of a birefringent periodically rocked fiber filter where coupling occurs between the two orthogonally polarized modes that are aligned with the birefringence axes of the fiber is considered. In the simulations, a bell-shaped input pulse is injected into one polarization mode: for different input peak powers, the energy present in the same mode at the output of a coupler, which is one or two coupling lengths long, is calculated. The nonlinear temporal broadening, due to the combined effect of group velocity dispersion and self-phase modulation, sets a fundamental lower limit to the time width of the input pulses. When pulses shorter than this critical value are used, the power-dependent energy switching characteristics of a device one coupling length long gets substantially spoiled. Effects related to the finite spectral bandwidth of the fiber filter are discussed. Numerical simulations are compared to recent experimental results on the self-switching of picosecond pulses in the visible (615 nm) with a birefringent rocking fiber     

Performance parameters of a wavelength-division demultiplexer madewith a single 3×3 coupler optical fiber ring or loopresonator

The performance parameters of a two-channel demultiplexer made with a single 3×3 coupler fiber ring or loop resonator are evaluated theoretically. These parameters include crosstalk, output intensity of the selected channel, and channel separation. Their dependence on the parameters of the coupler and the fiber such as the coupling length of the coupler, kd, the phase change of the fiber delay line, &thetas;, and the round-trip amplitude transmission coefficient of the fiber ring or loop G, which is the product of the amplitude transmission coefficients of the coupler and the fiber delay line and the amplitude gain of the degenerate two-wave mixing, is investigated. It is found that the best performance can be obtained at G=1     

Spot size expansion for laser-to-fiber coupling using an integratedmultimode coupler

Efficient coupling of light from a semiconductor waveguide to an optical fiber is difficult to achieve due to the inherent differences in the spot sizes. The problem is particularly severe in the vertical dimension. The use of a uniform, untapered, intermediate coupler structure which consists of a multimode waveguide is proposed. This structure has potential for integrating with the semiconductor waveguide. The basic design rules for this coupler are worked out using coupled-mode theory, and the detailed designs are based on direct calculation of the mode profiles in the coupler. A range of realistic examples is examined, and it is shown that the butt coupling efficiency from a typical semiconductor laser to an optical fiber can be improved by up to 5 dB. The dependence of performance on fabrication tolerances is also studied     

基于高双折射PCF的双Sagnae环高分辨率FBG解调系统

提出了一种基于高双折射光子晶体光纤（HB-PCF）的双Sagnac环的级联结构。理论计算表明,由光环形器构成的该级联结构,如双环中HB-PCF长度相等,与单环相比,可使干涉消光比增加1倍;实验中,双环结构输出干涉消光比达到43dB。基于边缘滤波器原理,实现了光纤Bragg光栅（FBG）高分辨率解调,静、动态应变分辨率分...     

2×2 fused fiber null couplers with asymmetric waist crosssections for polarization independent (<0.01 dB) switching

Polarization independent (<0.01 dB) switching is achieved at 1.55 μm in a strongly guiding, fused tapered fiber null coupler acoustooptic switch. An intermediate degree of fusion of the dissimilarly sized fibers is shown experimentally to have the form birefringence required to render the mode-splitting coupler polarization insensitive. The effect of the degree of fiber fusion on the acoustic wavelength of flexural waves is studied theoretically and experimentally, and precise control over the degree of fiber fusion is obtained for coupler waist cross-sectional dimensions as small as 6 μm     

Wavelength-selective fiber loop mirrors and their wavelengthtunability by twisting

Wavelength characteristics and the wavelength tunability of the fiber loop mirror constructed by a fused taper coupler are studied for elongation and twisting. The difference between the reflected and the transmitted wavelengths decreases exponentially with the number of minimal transmissions of the monitored light during fiber mirror fabrication. The fiber loop mirror twisted the constituent coupler can be realized as a fiber coupler and an equivalent waveplate for a theoretical study. The measured spectrum transmission agrees well with the theory. The reflected and the transmitted wavelengths can be tuned by twisting fiber mirrors without significant degradation. The wavelength change due to twisting is reversible and repeatable     

基于Sagnac干涉仪的级联型梳状滤波器

密集波分复用(DWDM)系统光信道数量的增加,使得与DWDM技术有关的各种光学滤波器技术成为当前光纤通信领域的研究热点.高双折射(HiBi)光纤环具有易于制作、性能稳定以及良好的滤波特性等特点,近年来受到广泛关注;通过增加Sagnac环内HiBi光纤和偏振控制器的个数,或者采用多个HiBi光纤Sagnac环的级联形式,...     

保偏光纤耦合器波长耦合比研究

根据单模光纤模激励理论,论述了熔融拉锥型光纤耦合器的工作原理,得出了耦合器耦合比和波长的关系,并对保偏光纤耦合器的耦合比、波长与温度的关系进行了实际测试.     

Analysis of a fiber-optic passive loop-resonator gyroscope: Dependence on resonator parameters and light-source coherence

Analysis has been made of a fiber-optic passive loop resonator, the heart of the gyroscope. The performance characteristics are heavily dependent on the resonator parameters, such as coupling intensity loss of the input light, coupling coefficient between two fiber lines in an evanescent-field directional coupler, and losses of the light traveling in the fiber loop, as well as on the temporal coherence of the input light. A two input and two output system is considered for a passive loop-resonator gyroscope. Differential output operation of the two output signals is described.     

Power Transfer of a Parallel Optical Fiber Directional Coupler

This letter describes experimental results of a simple optical fiber directional coupler which picks up a small portion of the transmitted power in a main optical fiber transmission line without affecting the characteristics of the main line. This directional coupler consists of two fibers closely parallel in a certain coupling length; an index matching liquid, Si-oil, fills the coupling region. A 50-dB power coupling and 21=dB directivity are measured. Insertion loss is almost negligible. The measured power coupling is much larger than that expected by the simple coupling theory.     

Three-dimensional electromagnetic modeling of fiber-core effects onthe coupling characteristics of weakly fused tapered fiber-opticcouplers

Based on the full-wave formulations, which combine the finite element method add the boundary element technique, and the step-like approximation method, a three-dimensional (3-D) electromagnetic modeling approach is proposed in this work to investigate the fiber-core effects on the coupling characteristics of the weakly fused tapered couplers. We find the fiber cores have significant effects on the mode field patterns, coupling coefficients, and birefringence for the coupler with large normalized frequencies. The influence of the fiber cores on the coupling behavior for the real couplers, such as 3 dB power dividers, polarization beam splitters, and wavelength demultiplexing/multiplexing couplers, are also studied in 3-D view. It is found that the effects of fiber-cores in the weakly fused tapered couplers have to be considered for accurately modelling their coupling behavior, although the model with no core assumption can predict the trend of the coupling characteristics for the real couplers     

A 1.3 μm directional coupler polarization splitter by ionexchange

A glass waveguide polarization splitter for operation in the 1.3 μm wavelength region is reported. The device, which has a symmetric directional coupler configuration, exploits the stress-induced birefringence in K⁺-Na⁺, ion-exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations. Starting from the measured potassium concentration (refractive index) profile of the structure and utilizing a combination of the multilayer stack theory and the effective-index method, the normal mode propagation constants and mode field profiles are calculated to determine the polarization splitting length and the extinction ratio, and the results are compared with the experimental data. It is shown that in a given coupler, the splitting occurs at several wavelengths in the 1.0-1.45 μm range. A 25 mm-long coupler, fabricated by thermal diffusion of K⁺ ions in BK7 glass, exhibits an extinction ratio of 18.2 dB at 1.32 μm, in excellent agreement with the simulation results     

球聚焦型3×1光纤熔锥耦合器的研究

以线性耦合波方程为基础,采用散射矩阵的方法讨论了等三角分布的熔锥型3×1光纤耦合器,并用射线理论分析了球聚焦透镜光纤的端面效应。将未封装的3×3熔锥光纤耦合器在束腰处切断,并将锥端面熔成聚焦球端,利用光信号在光纤锥形区和球聚焦透镜中特有的传输和耦合特性,实现了光纤的耦合、连接和分束。结果表明:采用该方法耦合效率可达70%左右。同时大大增加了耦合系统的失调容差,降低了调试和封装的难度,因而有着广泛的实际应用价值。     

Numerical Analysis on Transmission Characteristics of a Bragg Grating Assisted Mismatched Fiber Coupler

Based on mode-coupled theory, a Bragg grating assisted mismatched fiber coupler is analyzed theoretically. At the same time, a detailed numerical analysis on transmission characteristics of the coupler is carried out when it considers the arcs of two fibers in the coupling region of the coupler or not, and the optimized design on the Bragg grating assisted mismatched fiber coupler for wavelength-division multiplexing/ demultiplexing is proposed.     

熔融拉锥过程中的偏振调制效应及应用

对光纤熔锥耦合器拉制过程中的偏振调制效应作了定性的理论分析,耦合区内的几何双折射和应力双折射导致的对称模和反对称模在x偏振方向和y偏振方向上的传播常数差不一致,从而引起两个方向的偏振光耦合的空间周期不同,存在相位差别,当相差正好达到π时实现偏振分离.在此基础上制作了熔锥型偏振分束器,消光比达到了16.5dB.