Absorption loss in optical fibres due to hydrogen

It is shown that OD formation in optical fibres due to the deuterium molecule can become a barrier to OH formation in optical fibres exposed to hydrogen, although it cannot be a barrier to the absorption due to the hydrogen molecule in a fibre. The mechanism is discussed.     

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.     

Attenuation changes in optical fibres due to hydrogen

The attenuation in an optical fibre due to dissolved hydrogen has been studied experimentally and theoretically as a function of time as the hydrogen is allowed to escape. The agreement confirms that the hydrogen is in molecular form and that the diffusion constant is 1 5×10?11 cm2/s at room temperature.     

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.     

Long-term loss stability of single-mode optical fibres exposed to hydrogen

The rate of increase in loss in single-mode optical fibres exposed to hydrogen at temperatures up to 150°C has been determined. Extrapolation down to ambient temperature of effects other than that due to interstitial hydrogen indicates that slow long-term loss increments at 1310 nm will remain less than 0.02 dB/km after 25 yr at 20°C in one atmosphere of hydrogen.     

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.     

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.     

Hydrogen permeation in optical fibres with hermetic carbon coatings

Hydrogen permeation has been measured for optical fibres with hermetic carbon coatings. Data obtained at elevated temperatures and high hydrogen pressures lead to predictions of extremely low permeation rates at typical operating conditions. In situ loss measurements have shown the existence of a lag time, during which no hydrogen reaches a fibre's interior     

Practical barrier to hydrogen diffusion into optical fibres

The diffusion of hydrogen (at 65 atm) into optical fibres coated with silicon oxynitride is found to be several orders of magnitude lower than that for uncoated fibres. Extrapolation of the data using a diffusion model predicts that such coatings should provide a practical and effective barrier against lower hydrogen pressures over system lifetimes. Thus all hydrogen-related optical ageing effects are significantly reduced.     

Reduction of loss due to OH in optical fibres by a two-step OH ? OD exchange process

An isotopic exchange process is used to convert the OH in optical fibre preforms into OD. The OH first overtone absorption is reduced from 80 dB/km to 1.5 dB/km. The OD second overtone absorption at 1.26 ?m is less than 0.5 dB/km.     

Scattering due to irregularities on dielectric or optical fibres

The effect on mode propagation of small (with respect to wave-length) irregularities or imperfections in a dielectric waveguide is analysed. Asymptotically, for large frequencies, the power which is scattered in the form of radiation (not guided) has an ?2 behaviour, and that scattered into the modes obeys a 1/?2 relationship. At the frequency of paramount interest for optical communication (cutoff for TM01 mode), the radiated power is 22dB larger than the power scattered into the HE11 mode.     

Radiation-induced loss and colour-centre concentration in optical fibres

The number of colour centres generated by gamma radiation has been measured with the ESR method; radiation-induced loss was obtained during the steady-state irrediation. By comparing these data, the induced loss in Ge/P-doped GI fibres corresponding to one colour centre is estimated to be 5.5 × 10?15 dB/km.     

Prediction of loss minima in infra-red optical fibres

Loss minima in two fluoride glass and chalcogenide glass fibres were calculated. The intrinsic losses are predicted to be 1 × 10?3 dB/km at 3.4 ?m for BaF2-GdF3-ZrF4 glass fibre, 1 × 10?2 dB/km at 2.7 ?m for BaF2-CaF2-YF3-AlF3 glass fibre and 1 × 10?2 dB/km at 4.5 ?m for GeS3 glass fibre.     

Transmission limitations due to fiber nonlinearities in optical FDMsystems

Transmission limitations due to stimulated Brillouin scattering and four-wave mixing processes are investigated for optical frequency division multiplexing (FDM) systems. The applicability of the dispersion-shifted (DS) and nondispersion-shifted (NDS) fibers is discussed, taking account of channel frequency separation, total channel numbers, input signal power, transmission length, and receiver sensitivity degradation. Experimental results on Brillouin gain spectra and the wave generation efficiency in four-wave mixing processes are also presented to discuss the applicability of the two types of single-node fiber. It was found that NDS fibers operated at a wavelength of 1550 nm can be widely deployed in multichannel systems both for the long-haul and information distribution transmissions, if the signal waveform distortion due to fiber chromatic dispersion is precluded. The delay equalizer will be useful for a high-speed system employing bit rates over 10 Gb/s and repeaterless spans over 300 km. For such an application, DS fiber is preferable. Concerning information distribution network applications, the NDS fiber should be more attractive as a transmission medium for FDM system applications     

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.     

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 behaviour of PCVD fibres in H2 atmosphere

The long-term irreversible loss increase of conventional GeO2-doped PCVD fibres in H2 atmosphere at room temperature is almost negligible. Purely F-doped fibres show virtually no H2-induced irreversible loss effects, even at high temperatures.     

光缆氢损的实例解析

针对光缆成缆的氢损提出一个验证实例及方法,希望引起相关产业对成缆材料的选择与相容性试验的重视。     

Loss spectra of optical fibres under hydrogen and deuterium

Assignment of the frequencies at the loss peaks due to hydrogen permeation is clarified on the basis of the loss spectra in silica glass fibre under deuterium. As a result, it is concluded that the loss peaks due to hydrogen permeation in silica glass fibre are related to the combinational vibrations of hydrogen molecular vibration and SiO4 tetrahedral vibrations.     

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.