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.     

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.     

Increased attenuation in optical fibres caused by diffusion of molecular hydrogen at room temperature

A new set of absorption peaks has been observed at wave-lengths between 1.5 and 2.5 ?m in silica-based optical fibres which have been exposed to hydrogen at room temperature. The largest peak, at 2.42 ?m, is identified as being due to the fundamental molecular hydrogen vibrational absorption. Other peaks in the set are related to the fundamental with the same energy shifts as previously reported for the first overtone spectrum. The implications of both sets of peaks are quantified for the operating windows of optical fibre systems at 1.3 and 1.55 ?m.     

Hydroxyl group formation caused by hydrogen diffusion into optical glass fibre

Transmission loss increase of optical glass fibre caused by hydrogen diffusion is measured as a function of temperature and partial pressure of hydrogen gas. The activation energy of hydroxyl group formation from the diffused molecular hydrogen was found to be 15.9 kcal/mole. Also the hydroxyl absorption loss increase at 200°C was found to be proportional to the square root of the partial pressure of hydrogen gas.     

Practical low-loss lens connector for optical fibres

A connector is described in which two lenses make a 1-1 image of the emitting fibre end upon the receiving end. This type of connector is not sensitive to surface contamination, radial offset and separation. It contains no high-precision components and the prealignment procedure is very simple. Average losses of 1.0 dB were obtained, which can be improved to 0.65 dB if antireflection coatings are used.     

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.     

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.     

Effective index drift from molecular hydrogen diffusion inhydrogen-loaded optical fibres and its effect on Bragg gratingfabrication

When hydrogen loading is used to enhance the photosensitivity of silica-based optical waveguides and fibres, the presence of molecular hydrogen dissolved in the glass matrix changes the effective index of propagation of guided optical modes by as much as 0.05%. Real-time monitoring of the reflectivity spectrum of Bragg gratings written in such conditions shows that the centre wavelength follows the changes in hydrogen concentration due to diffusion and reaction with glass defects     

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.     

Chemical change from diffused hydrogen gas to hydroxyl ion in silica glass optical fibres

The chemical change from hydrogen gas that diffuses into silica glass for optical fibres to hydroxyl function has been investigated. Hydrogen molecules that diffuse into GeO2-doped silica glass at 500°C easily change into OH ions by thermal energy, while this chemical change does not occur in pure silica glass at 500°C. Also, germanium-doped silica fibre, in which hydrogen gas is dissolved at room temperature, shows OH ion absorption loss increase with chemical change by heat treatment at above 100°C, while pure silica core fibre shows no OH ion absorption loss increase by the same treatment.     

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.     

Transverse light coupling from GaAs lasers into optical fibres

We report a method for transverse light coupling from GaAs lasers into optical fibres. The fibre end is positioned perpendicular to the laser-beam direction and is cut at the end under 45° to reflect the laser radiation. We measured 10% coupling efficiency for a plastics fibre which was simply cut by a blade. We used this method for an automatic-gain-control circuit and picked up reference light from the back side of a d.h. laser.     

Practical machine for electric arc splicing of optical fibres in the field

A portable machine is provided with a 7 cm × 5 cm daylight screen where a stereogram of the fibre ends is displayed. Easy adjustment is made without first cleaning the supports. The fibres are then polished, butted and welded automatically. Average losses of 0?06 dB arc obtained with graded-index fibres.     

Limits to power transmission in optical fibres

Measurements of the transmission characteristics of a multimode fibre have been performed to determine the power throughput limitations set by Raman scattering. The results show that, in the presence of severe pump depletion, the total transmitted power is effectively determined only by the fibre loss.     

Study of hydrogen diffusion in boron/germanium codoped optical fiber

Presents a novel technique for studying the dynamics of hydrogen diffusion in optical fiber. It shows that the hydrogen contributes directly to the effective refractive index of the fiber by its dielectric susceptibility. It provides a simple theory that relates the refractive index change to the total hydrogen concentration in the fiber core. It also deduces that there is a small contribution of less than 5% to the refractive index through the photoelastic effect. A low-finesse fiber Bragg grating Fabry-Perot interferometer allows the determination of the evolution of the hydrogen concentration in situ. The experimental results obtained for isothermal and isobaric diffusion between 45/spl deg/C and 90/spl deg/C yielded values for the parameters of Arrhenius-type expressions for the diffusivity, permeability, and solubility of hydrogen in germanium/boron codoped single-mode fiber. In addition, least squares curve-fits for outdiffusion yielded the gas-phase mass-transfer coefficient as a function of temperature.     

Low-temperature diffusion of indium into germanium assisted by atomic hydrogen

Indium diffusion stimulated by an energy release due to molecule formation from atomic hydrogen is studied. Germanium n-type crystals with a deposited indium film 0.2–0.3 μm thick were exposed to atomic hydrogen over different periods of time (up to 2×10⁴ s) at approximately room temperature. Indium diffusion into germanium was studied using laser mass spectrometry and X-ray structural analysis, and also by measuring the transmission spectra in infrared region of the spectrum. Based on the data obtained experimentally, mechanisms of stimulated heterodiffusion and accompanying processes are proposed. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 3, 2001, pp. 301–304. Original Russian Text Copyright ? 2001 by Matyushin.     

Frost-resistant coated optical fibres

Investigations of optical fibre losses in the range from -100°C to 20°C have shown that silicone crystallisation causes a significant loss increase in coated MCVD fibres, irrespective of the secondary jacket material. The application of noncrystallised silicone has provided a low level of the excess losses at low temperatures.     

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.     

Realistic efficiency of coupling light from GaAs laser diodes into parabolic-index optical fibres

More than 500 laser diodes have been coupled to graded-index fibres using microscopic glass beads for a proper injection into the fibre core. The coupling efficiencies have a good reproducibility and a high average value.