Loss increase for optical fibers exposed to hydrogen atmosphere

Loss spectrum changes for optical fibers exposed to a hydrogen atmosphere in the15-200degC temperature range are measured. Loss increase due to molecular hydrogen dissolved into fibers is investigated from the loss peak at 1.24 μm, and that due to hydroxyl group formation from the loss peak at 1.41 μm. The loss increase due to molecular hydrogen is fully explained by physical solubility theory and diffusion equation. The empirical formula for time, temperature, and hydrogen-pressure dependences of the loss increase due to hydroxyl group formation is evaluated from the experimental results. The loss increase at 1.3- and 1.5-μm wavelength band at room temperature are estimated.     

Dopant effect on transmission loss increase due to hydrogen permeation

The transmission loss increase due to hydrogen permeation in a GeO2-doped silica fibre and a P2O5-doped silica fibre are investigated. As a result, the difference of the loss increase between them is observed, and is considered to be due to the difference of the electronegativity between silica, germanium and phosphorus.     

Photobleaching effect on visible-region loss increase for heat-treated optical fibres in a hydrogen atmosphere

The photobleaching effect on the visible-region loss increase due to hydrogen was observed for the first time by argon-ion laser light launching in fibres. A 660 nm fluorescence intensity reduction for the bleached fibres was also observed.     

Optical transmission loss in liquid-core hollow fibers

Multimode optical fibers consisting of glass cladding and liquid core have been constructed. For a cladding index of refraction of 1.52 and a core of bromobenzene, index of 1.560, a loss of 0.140 dB/m has been measured over lengths of about 50 m. The loss measured with incoherent light is higher due to the presence of higher order modes. Strong absorption in the near infrared occurs in narrow wavebands associated with overtones of the C-H fundamental vibration frequency.     

Germanium-dopant effect on hydroxyl loss increase in optical fibers

The germanium-dopant effect on hydroxyl loss increase in optical fibers is studied experimentally. The distribution profile of hydroxyl absorption which is caused by hydrogen diffusion is measured for GeO2-doped silica glasses. From the experiment, it is found that the distribution profile of induced hydroxyl absorption is similar to the GeO2concentration profile. Moreover, the absorption loss increases due to hydrogen diffusion are measured for GeO2-doped silica fibers. From the experiment, it is concluded that the induced molecular hydrogen loss as well as the induced hydroxyl loss increases with an increase in the GeO2concentration.     

Effects of hydrogen diffusion on optical fibre loss increase

The time dependence of fibre loss increase due to hydrogen diffusion for different pressures and temperatures is reported. It is found that the optical fibre loss increases with increasing hydrogen pressure as well as temperature, and decreases with increasing temperature when removed from the hydrogen environment.     

Wavelength-dependent optical loss increase in graded-index optical fibre transmission lines

Wavelength-dependent optical loss increase in GeO2-P2O5-doped graded-index optical fibre transmission lines has been observed. The loss increase is found to depend strongly on the P2O5 concentration. By reducing the P2O5 concentration, loss increases at 1.3 ?m can be suppressed to a sufficient extent without any hindrance for practical usage.     

Transmission loss increase in optical fibres due to hydrogen permeation

The experiment of soaking the optical fibre cable in water is carried out. As a result, a tremendously large transmission loss increase is observed at 1.24 ?m. Through a fundamental experiment, it is shown that hydrogen permeation causes the transmission loss increase in optical fibres.     

Infrared loss increase phenomenon of coated optical fibers at high temperatures

The loss increase phenomenon of coated optical fibers at high temperature has been studied. The wavelength dependent loss increase, observed for plastic-coated fibers at 200°C, is found to be irreversible. During heating, the absorption peak of second overtone of Ge-OH preferentially appeared. The dependence of the loss increase on temperature, heating time, and dopant is also examined. The loss increase level is strongly dependent on phosphorous concentration. The experimental results indicate that the loss increase is caused by chemical reactions between fiber constituent materials and hydrogen generated from coating materials. It is also confirmed that the heating test of secondary coated fiber is a practical, useful method to evaluate the hydroxyl loss increase of optical fibers.     

千岛湖复杂地形条件下传播损失的估计与现场测量

湖区、港口近海、多山浅海等复杂地形条件下声传播建模难度大、距离相关的逐点测量过程复杂,本文提出使用UUV（Unmanned Underwater Vehicle）平台进行现场测量,其具有机动性强、快速高效等优点。本文使用统计学方法来处理湖试实验数据,同时用BELLHOP模型对信道仿真建模并估计传播损失参数。对比发现,当声源在恒温层时仿真与实测相符,在负梯度层时相差较大,主因在于湖区地形和底质的复杂多变导致触底声波的折射与吸收难以估计。实验说明复杂地形环境中传播损失的估计仍需依赖现场测量,而使用UUV平台的快速测量法是一种高效可靠手段。      

Fibre loss increase due to hydrogen generated at high temperatures

The loss changes at 1.39 and 1.88 ?m are measured for various nylon-jacketed fibres at a high temperature of 200°C. The loss increase at 1.39 ?m is due to the Si-OH-bond formation, and that at 1.88 ?m is caused by the absorption of hydrogen molecules in the silica glass. It is found that the loss increase due to the OH-bond formation is in proportion to the time-integrated concentration of the generated hydrogen molecules.     

Estimation of accurate effective loss rate for FEC video transmission

We propose an algorithm for adjusting data transmission parameters, such as the packet size and the code rate of forward error correction (FEC), to obtain maximum video quality under dynamic channel conditions. When determining transmission parameters, it is essential to calculate an accurate effective loss rate that reflects FEC recovery failures and over-deadline packets. To this end, we analyze the delays caused by FEC coding and the potential packet size variations. In our analysis, we consider the effect of delayed transmission of video packets incurred by the parity packets as well as the encoder and decoder buffers. With the analysis reflecting the delay effect, we are able to accurately estimate the delay patterns of all video packets. Based on the analysis results, we establish an accurate model for estimating the effective loss rate. Simulations show that the proposed effective loss rate model accurately estimates the effective loss rate and significantly improves the reconstructed video quality at the receiver.     

Transformation of interface states in silicon-on-insulator structures under annealing in hydrogen atmosphere

Changes induced by annealing the spectrum of states on a Si/SiO₂ interface obtained by direct bonding and on a Si(substrate)/〈thermal SiO₂〉 interface in silicon-on-insulator (SOI) structures were investigated by charge-related deep-level transient spectroscopy. The structures were formed by bonding silicon wafers and slicing one of the wafers along a plane weakened by hydrogen implantation. The SOI structures were annealed at 430°C for 15 min in hydrogen, which corresponded to the conventional mode of passivation of the Si/SiO₂-interface states. The passivation of interface states by hydrogen was shown to take place for the Si/〈thermal SiO₂〉 interface, as a result of which the density of traps substantially decreased, and the continuous spectrum of states was replaced by a band of states in the energy range E _c=0.1–0.35 eV within the entire band. For the traps on the bonded Si/SiO₂ interface, the transformation of the centers occurs; namely, a shift of the energy-state band is observed from E _c=0.17–0.36 to 0.08–0.22 eV. The trapping cross section decreases by about an order of magnitude, and the density of traps observed increases slightly.     

Molecular hydrogen behaviour for loss increase of silica fibre in cable filled with water

Evaluation of molecular hydrogen diffusion into silica fibre, which causes a loss increase at 1.24 ?m wavelength, and the accumulation mechanism for hydrogen in cable are reported. It has been found that loss increase around 1.24 ?m wavelength due to hydrogen greatly depends on the ambient hydrogen pressure. The hydrogen pressure in LAP sheath cable easily increases due to metal corrosion and the sealing effect of the sheath.     

复杂大气条件下红外系统作用距离的估算

通过对海平面上水蒸气、二氧化碳含量对应大气吸收透过率的数据进行拟合,得出在3～5 μm和8～13 μm大气窗口,水蒸气吸收透过率与可降水分,二氧化碳吸收透过率与海平面路程长度的关系.并依据相关文献进行高度和斜程修正.分析了大气对红外辐射的散射衰减以及总衰减.在此基础上基于MRTD法和约翰逊准则给出了扩展源目标红外辐射作用距离的估算方程.综合考虑了目标形状、大气能见度、海拔高度、目标天顶角和空间频率以及探测概率等多种因素对热成像系统作用距离的影响,给出了作用距离估算实例及结果.     

Bend loss in single-mode fibers

In this paper, we present the results of extensive single-radius bend loss measurements for two different fibers over wide ranges of wavelength (800-1600 nm) and curvature radius (13.5-27.5 mm). A new bend loss formula is also derived, allowing a good fit of experimental data over the whole range of both parameters. Using an equivalent step-index (ESI) approach we obtain a good agreement between estimated and real parameters: e.g., cutoff wavelengths are within 1%     

Leaky-mode loss in coated depressed-cladding fibers

A simple formula for the leaky-mode loss in realistic depressed-cladding (DC) fibers is presented. It takes the finite dimension of the substrate cladding and the presence of the coating into account. The losses show oscillations versus both the wavelength and the width of the substrate cladding. Additional small humps occurring in the transmission curves of cutoff measurements are well explained     

Model for hydrogen aging in multimode fibers

In order to explain the variation of initial aging rate on the square root of the hydrogen pressure observed in two other studies, a model based on the production of hydrogen atoms by some defect site in the glass is developed. The model is then successfully tested against the detailed temporal behavior that was reported for fibers containing high levels of phosphorus as well as those containing low levels     

Solitons in dispersion-compensated optical fibers with loss

A dispersion-compensated optical fiber is proposed for optical soliton propagation. The scheme is studied by a variational approach. Numerical analyses show that the proposed scheme can retain the soliton property for a much longer distance than normal systems. It is shown that, after 48 km, the pulsewidth in the proposed system remains similar to the initial pulsewidth, whereas in the normal system, the pulsewidth has already reached 10 times the initial value. It is demonstrated that significant improvements in soliton propagation characteristics can be achieved by properly cascading fibers with different degrees of group velocity dispersion in finite steps     

Probability density function of polarization dependent loss (PDL)in optical transmission system composed of passive devices andconnecting fibers

This paper presents a probability density function formula for predicting the polarization dependent loss (PDL) in an optical transmission system composed of passive devices and connecting fibers. A new calculation technique, which enables the probability density function formula to be obtained theoretically, is used instead of the most complicated part of the Muller-matrix or Jones-matrix calculations, which has been thought to be necessary for analyzing PDL. This technique involves calculation of the transmission coefficients of the transmission system and its devices from their PDLs. In the theoretical development, the central limit theorem is used as the sole approximation. A Monte Carlo numerical simulation was done to verify the validity of the analytical theory. Very good agreement between simulation and analytical theory is obtained when the number of devices having PDL is four or more. An experiment also demonstrated the validity of the analytical theory. The theory can also explain some phenomena that occur in systems composed of optical amplifiers, even though it had originally been developed to explain PDL-related phenomena in systems composed of passive devices only