Raman spectra of hydrogen-treated optical fibres

Chemical reactions in a Ge-P-silicate optical fibre exposed to hydrogen at 100 bar and 150°C for times up to 120 h are studied by Raman spectroscopy. Hydride and hydroxyl groups are formed, as Si-H and P-OH. The reaction kinetics are consistent with a defect-related mechanism. The saturation concentration of hydroxyl is about 103 ppm.     

Time-domain interpretation of four-photon spectra from optical fibres

For a process where the pump power is divided between two modes the frequency shift is shown to be directly proportional to the intermodal delay, provided the material dispersion has the appropriate form. Results obtained with a vapour-axial-dispersion silica fibre demonstrate the subpicosecond resolution which is possible.     

Loss measurements of microstructured optical fibres with metal-nanoparticle inclusions

Optical losses of measured optical fibres (MOFs) with silver nanoparticle inclusions are measured when visible light is guided in the core. The high pressure chemical deposition technique used to deposit the metal offers good control of the particle sizes allowing for varying transmission properties. The low losses demonstrate the potential for the silver impregnated MOFs to be integrated with conventional optical fibre devices.     

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.     

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.     

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.     

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.     

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.     

Fusion splicing between optical circuits and optical fibres

Splicing between an optical fibre and a planar deposited silica waveguide was performed by using a CO2 laser as a heat source. The average splicing loss of 30 samples between a multimode graded-index fibre and a deposited silica waveguide was 0.18 dB. Reflection from the joining point disappeared by the fusion splicing.     

Loss model for singlemode fibres

A modified Hanson model is proposed for the estimation of spectral loss. The approach to developing the model is based on multiple regression analysis. The model predicts spectral loss by using a vector containing the attenuation at three specified wavelengths of 1.31, 1.37, and 1.38 mu m. The estimated errors between the measured and predicted losses are less than 0.02 dB/km in the 1.23-1.60 mu m wavelength region. This model will enable system designers to optimise systems with respect to the wavelength region without the need to use difficult procedures.<>     

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.     

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.     

Spark-induced fracture of optical fibres

Sparks can be used to induce the fracture of optical fibres under controlled conditions to prepare ends for low-loss joints. The material and geometry of the electrodes of the spark gap are found to have a pronounced effect on the efficiency of the technique.     

Loss increases due to chemical reactions of hydrogen in silica glass optical fibers

Loss increases due to the chemical reactions of hydrogen are investigated for GeO2-doped, GeO2. F-doped, and pure silica core fibers. Dissolved hydrogen gas causes the hydroxyl loss increase as well as the short-wavelength loss increase in the first two fiber types at high temperatures. The short-wavelength loss increase is attributed to two kinds of ultraviolet absorption increases. Doping fluorine reduces both of these loss increases as well as enhances the activation energy of the hydroxyl formation.     

Fusion splicing of optical fibres

A portable optical-fibre field fusion-splicing set has been designed and tested. The equipment includes the provision of a protective package over the completed splice. Average insertion losses of 0.2 dB were achieved with a 75 ?m core-diameter graded-index fibre.