Optical fiber cables using V-grooved cylindrical units: High performance cables

Some practical and theoretical aspects of a V-grooved cylindrical cable (high performance optical fiber cable) are now being developed in several countries. Design of cables is important, because bendings may cause distortions. In order to limit micro-bending losses in an optical fiber cable, it is possible to modify parameters relating to the fiber or the cable. Some of the possibilities are: to decrease the core diameter in order to decrease the attenuation coefficient; to increase the diameter of the cladding so as to increase the tension above which micro-bendings occur; to increase the continuous bending radius due to cabling; to decrease the effects of roughness (μ); to integrate the effects of roughness as much as possible by decreasing the Young modulus of the coating and of the cable material and by increasing the cladding thickness; and to suppress the tension T of the fiber in the cable. The cabling element is made of a V-grooved cylindrical core, in which the fiber with an outside diameter d_e (outside diameter or primary coating) are laid without tension, with a slight excess length. The slots with a depth h are helical or alternated helical, providing the possibility of additional excess length, and the fiber can be “cabled” directly without stresses. A central strength member with a diameter Dp reinforces the cylindrical rod, ensuring the mechanical and thermal qualities.     

Origin of temperature dependence of microbending attenuation in fiber optic cables

Abstract

Temperature-induced changes in the attenuation of multimode optical fiber cables are shown to be caused by mismatch between the thermal expansion coefficients of the fiber and the cabling materials. A quantitative theoretical model of low temperature loss, based on the formation of fiber microbends by microvariations in the jacket concentricity, is described. This model applies to tightly jacketed, soft buffered cable designs. An equation relating the low temperature optical attenuation to cable parameters is derived using this model. Good agreement is obtained between this theoretical prediction and experimental results. The theoretical model is used to compare the effectiveness of different cable designs on reducing excess loss at low temperature.     

抗弯光纤的理论研究与制造

针对军事上光纤制导等方面的技术要求,从光纤波导的芯层相对折射率差、芯直径、下凹包层等结构参数方面研究了光纤抗弯曲性能,并且研究了光纤内涂层对光纤弯曲性能的影响。通过对光纤弯曲特性的深入研究后,采用PCVD工艺制造了专利技术的抗弯光纤,并测试了相关参数。     

Investigation of cladding and coating stripping methods for specialty optical fibers

Fiber optic sensing technology is used extensively in several engineering fields, including smart structures, health and usage monitoring, non-destructive testing, minimum invasive sensing, safety monitoring, and other advanced measurement fields. A general optical fiber consists of a core, cladding, and coating layers. Many sensing principles require that the cladding or coating layer should be removed or modified. In addition, since different sensing systems are needed for different types of optical fibers, it is very important to find and sort out the suitable cladding or coating removal method for a particular fiber. This study focuses on finding the cladding and coating stripping methods for four recent specialty optical fibers, namely: hard polymer-clad fiber, graded-index plastic optical fiber, copper/carbon-coated optical fiber, and aluminum-coated optical fiber. Several methods, including novel laser stripping and conventional chemical and mechanical stripping, were tried to determine the most suitable and efficient technique. Microscopic investigation of the fiber surfaces was used to visually evaluate the mechanical reliability. Optical time domain reflectometric signals of the successful removal cases were investigated to further examine the optical reliability. Based on our results, we describe and summarize the successful and unsuccessful methods.     

A colloidal crystal microstructure fiber: fabrication and characterization

A method of fabricating colloidal crystal microstructured fiber is presented. The proposed structure relies on partial etching of the cladding layer of a single-mode fiber and growth of colloidal photonic crystals inside eroded area. The photonic crystal cylindrical annulus embedded in fiber is characterized by optical and scanning electron microscopy. The optical characterization was analyzed by optical transmission spectroscopy. The measurement results show a about 1550-nm band gap. The results also reveal the possibility of cladding cylindrical fibers with three-dimensional photonic crystals.     

制导光纤1550 nm波长微弯损耗成因分析

从制导光纤本征损耗、预制棒制作、光纤拉制、涂覆与挤塑以及成缆工艺等方面分析造成制导光纤1550nm波长微弯损耗的原因。     

小直径单芯液晶聚合物挤塑光缆抗张强度的影响因素分析

从理论上分析了0.5 mm以下小直径单芯液晶聚合物（LCP）光缆在成型过程中,影响光缆抗张强度的主要因素,这些因素主要包括熔融液晶聚合物的温度特性、模芯和模套的结构参数、模芯与模套之间的距离以及光纤的放线张力及其牵引速度等,介绍了各影响因素与光缆抗张强度之间的相互关系,深入分析了光缆加强层厚度与其抗张强度系数之间的相互关系。实验结果证明:小直径液晶聚合物抗张强度与其加强厚度并不存在理想的线性关系,且在一定直径范围内,小直径液晶聚合物光缆具有相同数值的最大抗张强度。     

全光纤干涉式结构中传感模式仿真分析

全光纤干涉式传感结构中包层模场与外界物理量作用,携带被感测信息,因此对包层模的研究是设计制作和提高该类传感器传感性能的关键.利用有限差分光束传播法获得传感光纤不同长度和不同芯径比时传感器对应的光谱,通过傅里叶变换获得其干涉频谱,计算出各主要参与干涉的包层模组的有效折射率,利用色散方程确定对应包层模.理论仿真结果显示,随着传感部分光纤长度增加,参与干涉的包层模式随之增加,并且向高阶模式变化,光谱变得稠密,是多阶包层模干涉的叠加,传感器输出干涉谱的自由光谱范围变小.随着输入光纤与传感光纤芯径比变化,会明显改变纤芯包层功率分布,同时,芯径比增大也会增加参与干涉的包层模种类和阶数.     

Single-particle subband properties of quantum cables

We proposed a new kind of coupled coaxial cylindrical quantum wires structure - quantum cable, and calculated its single-electron energy subband spectrum for the varying structure parameters, in order to investigate its subband motion in the structure parameter space. It is shown that quantum cable has unique subband spectrum, which differs either from the (solid and hollow) cylindrical quantum wire or from the usual coupled double quantum wires (CDQWs) structure. Aside from the two-fold degeneracy induced by the cylindrical symmetry, crossings (accidental degeneracies) and anticrossings (repulsions) of quantum cable subbands with different azimuthal and radial quantum numbers are observed as one of the cable structure parameters varies. This introduces the dependence of the subband ladder on the structure parameters of the quantum cable structure. However, the subband with the lowest azimuthal and radial quantum numbers remains the lowest subband and never crosses with the other subbands irrespective of the value of structure parameters. As the coupling barrier is broadening (coupling becoming weak), some subbands bundling toward another subband is seen before the extreme isolating limit achieved. Moreover, the separation between neighboring subbands exhibits non-monotonous evolution as one changes the thickness of one of the cylindrical quantum wires, with a minimum existing in the separation between some two adjacent subbands. Interesting optical and transport phenomena arising from these unique subband properties of the quantum cable structure are also predicted. Received 22 March 2000 and Received in final form 6 June 2000     

High-sensitivity, fiber-optic, flexural disk hydrophone with reduced acceleration response

A hydrophone consisting of a hollow cylinder whose flexible, circular end plates are bonded to pairs of pat, spiral wound coils of optical fiber is described. When the end plate/disk is deformed due to a pressure difference, the outer and inner fiber coils experience opposite strains resulting in a “push—pull” optical path length difference which is detected in an all-fiber Michelson interferometer. The close proximity of the interferometric fiber coils, separated by the thin thermally conducting end plate, rejects thermal gradient-induced signals. The addition of a second identical end plate and fiber coil pair at the opposite end of the cylinder will double the acoustic sensitivity while canceling acceleration induced signals. The calculated and measured optical strain of a single simply supported plate, single-coil sensor (8.0 cm diameter, 3.0 mm thickness) using static pressure, acoustic pressure, and acceleration are in good agreement and yield a sensitivity of 0.21 rad/Pa (ΔΦ/ΦΔP = -301 dB re I μPa-1) below its resonance frequency of 3 kHz. The calculated and measured strain for a dual clamped disk (4.5 cm diameter, 1.0 mm thickness) acceleration-canceling sensor with four 8-m coils are in good agreement also and yield a sensitivity of 1.0 rad/Pa (ΔΦ/ΦpΔP = -291 dB re 1 μPa^-1) below the disk resonance frequency of 4.5 kHz. These are the highest fiber-optic, omnidirectional hydrophone sensitivities reported to date.     

Linear and nonlinear optical properties of carbon nanotube-coated single-mode optical fiber gratings

Single-wall carbon nanotube deposition on the cladding of optical fibers has been carried out to fabricate an all-fiber nonlinear device. Two different nanotube deposition techniques were studied. The first consisted of repeatedly immersing the optical fiber into a nanotube supension, increasing the thickness of the coating in each step. The second deposition involved wrapping a thin film of nanotubes around the optical fiber. For both cases, interaction of transmitted light through the fiber core with the external coating was assisted by the cladding mode resonances of a tilted fiber Bragg grating. Ultrafast nonlinear effects of the nanotube-coated fiber were measured by means of a pump-probe pulses experiment.     

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。     

Fiber optic cables for undersea communications

Abstract

Areas for potential use of low-loss optical fibers in undersea communications are discussed, along with constraints that should be satisfied in incorporating these fibers into practical cables. Recent progress in construction of optical cable units with low attenuation, small diameter, low specific gravity, high tensile strength, and extended flexural endurance is described. Design concepts for six undersea optical cables, with a variety of diameters and capabilities, are presented in detail. Guidelines are discussed for the design of such cables. Related operational requirements on the cable, such as power transfer, are examined to show how unconventional approaches can allow advantages of the optical data link to be more fully utilized.     

Particle size effect on porous Sol–Gel doped cladding U-shaped optical fiber critical micelle concentration (CMC) sensor

In this paper, a sol–gel derived coating U-shaped optical fiber sensors for measurement of critical micelle concentration of surfactants has been studied. The doped sol–gel cladding fiber was used to construct an active cladding U-shaped optical fiber CMC measurement sensor. The porous sol–gel film was deposited a 1000 m core plastic clad silica fiber after removing the cladding of the fiber at the middle portion nearly 6 cm and bending in U-shaped design. CMC detection is based on an adsorption effect in sample solution of sodium dodecylbenzenesulfonate. Three different types of particles size of sol–gel porous cladding were tested in our lab. Test results show that the sensitivity of the small particle size porous sol–gel cladding U-shaped optical fiber in sensing region is higher than that of large particle size sol–gel cladding based U-shaped. PACS 42.81.Bm; 42.81.Pa     

Evanescent-wave optical Cr VI sensor with a flexible fused-silica capillary as a transducer

A light-guiding, flexible fused-silica (FFS) capillary has been used in designing an optical fiber Cr VI sensor for monitoring Cr VI ions in water samples. The FFS capillary is similar to a conventional silica optical fiber in that it can guide light in the wavelength region from the UV to the near IR but different from a conventional optical fiber in that it is a tubular waveguide. The inner surface of the FFS capillary is fused silica, which one can modify to design an optical fiber chemical sensor. The FFS capillary has a cladding layer plus a protective polymer coating on its outside surface. The cladding layer ensures the ability of the FFS capillary to guide light. The protective coating increases the FFS capillary's mechanical strength and makes it robust for practical applications. Compared with conventional silica optical fibers, it is much easier and more feasible to use this FFS capillary to fabricate long-path (tens of meters to thousands of meters) evanescent-wave based chemical sensors. We describe a Cr VI sensor based on the intrinsic evanescent-wave absorption by Cr VI ions in a water sample filled inside the capillary as an example of use of a FFS capillary in chemical sensor design. This simple sensor, using a 30 m light-guiding FFS capillary as a transducer, has the capability of detecting as little as 31 parts in 10(9) of Cr VI in a water sample, which is close to the detection limit of some sophisticated, expensive analytical instruments.     

Design parameters influencing non-uniform current distributions in superconducting multi-stage stranded cables

We have suggested that non-uniform currents occur due to certain design parameters, for example a combination of cabling pitches, in a previous study. In the present study, we evaluate the occurrences of non-uniform current distributions in terms of design parameters, i.e., the combination of cabling pitches, winding methods (solenoidal and pancake winding) and cross-sectional shape of the cable by numerical analyses. Finally, some basic design concepts to solve this problem are proposed.     

液晶聚合物小直径光缆挤塑工艺研究

基于液晶聚合物挤塑法,提出一种研制小直径光缆的技术途径。描述了液晶聚合物的基本特性,说明了液晶聚合物是小直径光缆的理想挤塑材料。研究了小直径光缆的挤塑工艺参数并根据液晶聚合物的材料特性给出了挤塑工艺流程。采用挤塑方式研制出外径为0.45mm的液晶聚合物小直径光缆,分析了该光缆的基本性能。试验结果表明：挤塑工艺对光纤几乎不产生附加损耗,在-60℃～＋80℃的温度范围内,光缆的附加损耗几乎为零。     

Destruction of silica fiber cladding by the fuse effect

The phenomenon of destruction of silica fiber cladding by the fiber fuse effect has been observed for the first time to the authors' knowledge. Experiments on the optical discharge propagation along a fiber were conducted with fibers of decreased cladding thickness. The destruction of fiber cladding led to expansion of the optical discharge plasma and to a decrease of its density. This resulted in the termination of optical discharge propagation. The section of a fiber with decreased cladding thickness can act as a safety device to halt damage propagation.     

Characteristics of pure silica core single-mode fiber

Single-mode fibers with low attenuation and sufficient reliability are especially important for long-span optical transmission systems. Conventionally, GeO₂ has been added to the fiber core region in order to make a refractive index difference between the core and cladding. However, the addition of GeO₂ increases Rayleigh scattering loss [1], and deteriorates the chemical stability against hydrogen atmosphere and γ-ray irradiation to bring about an increase in attenuation. [2][3] Therefore, pure silica core single-mode fiber was considered to be an ideal type of fiber, and it was succeeded in being fabricated by utilizing fluorine containing SiO₂ cladding.     

Fiber optic cables for undersea communications

Areas for potential use of low-loss optical fibers in undersea communications are discussed, along with constraints that should be satisfied in incorporating these fibers into practical cables. Recent progress in construction of optical cable units with low attenuation, small diameter, low specific gravity, high tensile strength, and extended flexural endurance is described. Design concepts for six undersea optical cables, with a variety of diameters and capabilities, are presented in detail. Guidelines are discussed for the design of such cables. Related operational requirements on the cable, such as power transfer, are examined to show how unconventional approaches can allow advantages of the optical data link to be more fully utilized.