A 2 km Optical Fiber Communication Trial

This paper describes a recent field trial of an optical fiber communication link. The fixed point-to-point full duplex link used low loss multi-mode fibers fabricated by the CVD process in a simple cable structure. Fiber loss was approximately 4 dB/km before cabling and up to 7 dB/km after cabling. Digital 5 Mbit/s throughput TDM terminals were used to multiplex a variety of signal sources, including voice and data onto the fibers. Cabled fiber losses over 2.3 km were low enough to permit the use of incoherent infrared LED's as sources and silicon PIN photodiodes as receivers. 'Vee' groove splices were employed to connect fibers in the field. Installation was by standard cable laying techniques and no special problems were encountered.     

Fiber cable design and characterization

Optical-fiber cable design differs from the design of metallic cables principally because of two factors: i) the physical properties of fibers are more limiting than those of metals, and ii) the transmission performance of a fiber can be altered by cabling operations due to a phenomenon called microbending. After reviewing these factors, methods are considered for mitigating their effects by appropriate design procedures. This leads to the consideration of different types of cable structures. In order to evaluate an optical cable design, it is necessary that its important mechanical and optical properties be characterized. The tensile, bending, and impact performance, as well as cabling added loss, temperature dependence of loss, and concatenated fiber bandwidth are then considered. The paper concludes with a discussion of "long-term" stability of optical cables.     

Analysis of the Insertion Loss and Extinction Ratio of Two-Mode Fiber Interferometric Devices

The insertion loss and extinction ratio of an amplitude modulator and a 2×2 switch based on a two-mode fiber (TMF) interferometer butt coupled to one or two offset single-mode fibers are analyzed theoretically. Performance is shown to be limited by the asymmetric shape and small secondary lobe of the TMF mode pattern, which prevent full coupling to the single-mode fiber. For an amplitude modulator using a circular (elliptical) core TMF, applying a suitable offset between fibers and optimizing the fiber parameters, the loss can be minimized to 0.39 dB (0.23 dB); the extinction ratio is then 14.4 dB (16.9 dB). With a different offset, the extinction ratio can be made infinite, but the loss is then 0.95 dB (0.47 dB). Comparable figures are derived for a switch.     

Automated fusion-splicing of polarization maintaining fibers

An advanced splicing technique for polarization maintaining (PM) fibers has been derived based on the polarization observation by lens-effect-tracing (POL) method. With this technique, azimuthal alignment on common types of PM fibers can be automatically performed in a passive way by an automated fusion splicer. Because the method permits an accurate estimation of the splice's extinction ratio before and after actual splicing, the quality of the splice call be estimated without having to make an active measurement. The experiment results illustrated in the paper show a mean extinction ratio 32.2 with 2.73 dB standard deviation and mean difference between measured and estimated extinction ratio 0.18 dB, respectively, for six different types of PM fibers     

Single-mode fused biconical coupler optimized for polarizationbeamsplitting

A single-mode fused biconical coupler for polarization beamsplitting is described. In the coupling region, standard communication fibers are used. The output fibers are polarization-maintaining. To stop the coupler drawing process accurately, the degree of polarization is measured during the drawing and is used as a criterion. Losses of 0.2 dB are typical, and a minimum extinction ratio of -27 dB is achieved. A usable spectral window as broad as 17 nm with an extinction ratio smaller than -15 dB for both output fibers is obtained. Any specified wavelength for the minimum of the extinction ratio is reached within ±3 nm     

Analysis of a tunable single mode optical fiber coupler

We report the operation and the theoretical modeling of an efficient, tunable, and low-loss single mode fiber coupler. The coupler design follows a scheme previously reported, in which two optical fibers mounted in curved grooves in separate quartz substrates are polished until sufficient cladding material has been removed to permit optical coupling between the mated polished faces of the fibers. The results of a computer analysis of the distributed coupling taking place between the fibers are discussed, emphasizing the intuitive dependences of the coupling coefficient and effective interaction length of the device on its geometrical parameters. A detailed experimental analysis of fiber couplers follows in which we characterize two types of couplers made with different brands of single-mode fibers. Operation up to 100 percent coupling ratio and 50 dB extinction ratio between coupled and direct branch as well as operation in overcoupling regimes are demonstrated, both at visible and infrared signal wavelengths. Tuning curves are shown that emphasize the excellent tunability properties of such couplers in which the coupling ratio can be smoothly and continuously tuned between 0 and 100 percent. Experimental evidence of the relatively low loss level and very low polarization dependence of the fiber couplers are also presented. All experimental results, including an analysis of the influence of the refractive index of the intermediate layer of index-matching liquid between the polished faces of the fibers, are found to be very well predicted by our theoretical model.     

Theory of resonant absorption effect and its application tosingle-mode single-polarization fibers

A slight deviation from the resonant condition virtually stops the exchange of energy between two parallel fibers. When one fiber is birefringent, and the other isotropic and lossy, the energy of only one polarization mode swaps back and forth between two fibers and is eventually absorbed. The scalar wave equation is used to investigate the resonant effect. It is found that energy conservation is an intrinsic property of the solution of the scalar wave equation for any trial function, and that standard coupled mode equations obtained from Maxwell's equations can be derived from the scalar wave equation in an exact way. The resonant effect discussed can provide very high extinction ratio at extremely low penalty of additional loss. For example, an extinction ratio of 1.2×10⁴ dB with a penalty of 0.2 dB can be expected after 1-km transmission for waveguide parameters common in fiber optics     

基于波长扫描调制法测量保偏光纤的偏振特性

分析了保偏光纤偏振特性及其拍长和偏振消光比的基本测量原理,并根据单模保偏光纤基模的2个正交偏振模分量HEx11与HEy11间的相位差与波长的关系,推导出偏振拍长的测量关系式,提出了测量保偏光纤偏振特性的波长扫描调制法.采用此方法对熊猫型保偏光纤(YOFC-3367WY)的偏振特性进行了验证性实验研究.拍长和偏振消光比的测量结果表明,在该保偏光纤工作波长处试验结果与理论分析相当一致,说明该方法具有简单易行、测量精度高的优点.     

Polarization mode dispersion characterization of single-modeoptical fiber using backscattering technique

This paper presents a completely new method able to characterize polarization mode dispersion (PMD) properties of randomly birefringent single-mode fibers, using polarization sensitive backscattering technique. We show analytical relationships between evolution of polarization state of backscattered signal with respect to state of polarization of forward one. Our technique allows one to measure differential group delay, beat length, and correlation length at the same time over long single-mode fibers using only one fiber end. Experimental data fit very well with numerical results, confirming the capability of our technique for fast routine characterization of PMD during cabling, before and after installation     

Polarization-maintenance limits in polarization-maintaining fibersand measurements

Intrinsic, extrinsic, and measurement-related polarization-maintenance transmission performance limitations are determined on short fiber lengths of hybrid-rectangular polarization-maintaining fibers and compared with previously reported limits. A direct polarization intensity extinction ratio -52.4±0.04 dB was obtained using automated measurement techniques. System measurement capability is limited by the lenses to -60 dB. Polarization-maintenance transmission limitations in the measurement polarizers and in cladding modes for short polarization-maintaining fibers were found to be negligible. New polarization-maintenance limits are presented to provide more precise measurement of the performance of short polarization-maintaining fibers     

High performance fused-type mode-selective coupler using ellipticalcore two-mode fiber at 1550 nm

In this letter, we demonstrate a high performance fused-type mode selective coupler that couples the LP₁₁ mode in one fiber and the LP₀₁ mode in another using highly elliptical core two-mode fibers. The phase-matching condition was achieved by etching and prepulling portions of two-mode fibers. The coupling efficiency and the mode extinction ratio of 56% to 80% and 22-32 dB, respectively, were achieved with high temperature stability over 1515- to 1595-nm wavelength range     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

Numerical and experimental analysis of polarization properties from hybrid PCFs across different photonic bandgaps

This work presents a numerical and experimental characterization of polarization properties from hybrid photonic crystal fibers (hybrid PCFs or HPCFs) across different bandgaps. Very high extinction ratio over at least three wide bands and single-mode and single-polarization operation over more than 320 nm have been obtained by using only one fiber. Furthermore, it is reported, for the first time, a multi- and broadband fiber-based optical polarizer. Numerical simulations and experiments of modal, birefringence and polarization properties have been carried out to demonstrate the remarkable performance of the proposed device.     

考虑多次散射的卷云几何特征和光学特性反演方法

研究了考虑多次散射的卷云几何特征和光学特性反演方法,对反演卷云高度和卷云激光雷达比的方法进行了改进。采用多次散射因子对卷云消光系数曲线进行修正,选取云底及云顶附近高度消光系数变化率的均值求解云层高度修正误差,对微分零交叉法求解得到的卷云高度进行修正,实现了较为精确的激光雷达云层高度反演。采用以边界值处消光系数和卷云光学厚度为约束条件的粒子群算法,求解卷云有效激光雷达比,选用半解析Monte Carlo方法,计算总散射信号与一次散射信号的比值,并结合Platt多次散射因子方程求得多次散射因子,实现了卷云激光雷达比的准确求解。使用Mie散射激光雷达真实回波信号进行了验证。结果表明,该改进方法具有较高的精度,更具应用价值。     

Angled-facet S-bend semiconductor optical amplifiers for high-gainand large-extinction ratio

The extinction ratio of an optical gate with a spot-size-converter-integrated semiconductor optical amplifier (SSC-SOA) is deteriorated following the direct coupling of unguided light between the input and output fibers. In this letter, an S-bend waveguide structure is introduced into an active waveguide to suppress such direct coupling. Angled facet structures are also introduced for obtaining low facet reflectivity. The fabricated SSC-SOA operating at 1.55-μm wavelength achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 20 dB     

A novel polarization splitter based on the photonic crystal fiber with nonidentical dual cores

A novel polarization splitter based on photonic crystal fibers (PCFs) with two nonidentical cores is proposed. The two highly birefringent cores are vertically arranged to obtain polarization selective coupling. The horizontal polarization exchanges its energy between the two cores. However, the vertical polarization shows little coupling between the two cores. This is achieved in single-material glass waveguides for the first time to our knowledge. The PCF-based polarization splitter exhibits many advantages such as shorter length, high extinction ratio, and wide bandwidth over its counterparts.     

Effect of cabling on polarization mode dispersion in optical fiber ribbon cables

This paper theoretically and experimentally investigates an effect of cabling on polarization mode dispersion (PMD) in ribbon fibers helically stranded in optical fiber ribbon cables aimed at designing low PMD ribbon cables. Based on the birefringence model focused on the change in the birefringence when ribbon fibers are cabled, the helical pitch of optical fiber ribbon cables is designed to minimize the maximum PMD in the cables. A low PMD characteristic is confirmed in optical fiber ribbon cable with approximately the optimal helical pitch.     

聚合物微结构光纤型可调衰减器的研究

设计了一种基于聚合物微结构光纤(PMOF)及液晶选择注入技术的温控可调衰减器.拉制了高质量的聚甲基丙烯酸甲酯(PMMA)PMOF,并在光纤微孔中实现了选择性注入液晶5CB,制作了温控可调衰减器,器件消光比超过60 dB.实验结果与理论设计基本吻合.     

Tightness estimation of fiber ribbons in a slot-type single-modeoptical-fiber cable

Tightness of fiber ribbons in a slot-type cable is estimated by measuring the temperature dependence of fiber strain due to temperature change for free fiber ribbons and those assembled in a cable. Fiber-strain measurements were carried out by an optical heterodyne detection technique for free nylon-jacketed and liquid-crystal-polymer (LCP)-jacketed fiber-ribbons, and for the cabled fiber ribbons. By comparing the thermal behavior of fiber strain for both states of jacketed fibers, it is found that the fiber ribbons are tightly accommodated in the slot-type cable in temperature regions over -15°C for nylon-jacketed fiber ribbons and 0°C for LCP-jacketed fiber ribbons under additional fiber-strain value of 0.015% through the cabling process. The fiber ribbons, which are tightly accommodated with suitable tension level through the process at room temperature, show reasonable thermal-strain behavior in comparison with the initially introduced fiber strain during the cabling process     

非金属型软光缆的研究

文中就非金属型软光缆的结构，材料，有关工艺及性能实验和实际应用中进行了讨论。还介绍了作者所开发的一些有代表类型光缆的结构和性能，各种光缆在满足机械及环境性能的同时，光衰减可保持原始光纤的水平。