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.     

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     

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.     

Attenuation/time relation for OH formation in optical fibres exposed to H2

The increase in attenuation due to POH and GeOH formation, when fibres are exposed to hydrogen, has been found to follow a log (time) relation. Results are given for fibres with different phosphorus content. A possible explanation for the log t behaviour is discussed and, using the relationship, a prediction of long-term attenuation rise is made. The rise thus predicted is very small for current low-phosphorus fibres.     

Infra-red optical loss increase for silica fibre in cable filled with water

Loss increase characteristics of optical fibre in cable filled with water are reported. Drastic loss increase around 1.24 ?m is observed for both graded-index and single-mode fibres. The origin of the loss increase is found to be due to hydrogen gas diffused into the silica glass interstitially.     

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.     

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.     

Influence of Hydrogen on Optical Fiber Loss in Submarine Cables

Characteristics of the loss increase in optical fibers due to hydrogen permeation are described, and it is shown that the loss increase due to OH formation in GeO2-doped single-mode fibers is thought to be small compared to the loss increase due to the vibration of hydrogen molecules even in 20 years. Furthermore, the hydrogen generation due to electrochemical reaction in the optical cables is described. Finally, the countermeasure against the problem is discussed.     

Photoelectric instability in optical fibre resulting in spontaneous second harmonic generation

The self-organised second harmonic generation (SHG) in optical fibres is explained as a consequence of a convective instability leading to spontaneous formation of the chi /sup (2)/ grating due to the growth of small fluctuations. The authors show that the observed SHG should be interpreted as amplification of noise.<>     

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.     

Hydrogen-induced loss increases in germanium-doped single-mode optical fibres: long-term predictions

A spectrally broad loss increase occurs in GeO2-doped optical fibres exposed to hydrogen at elevated temperatures. This is the primary H2-induced loss mechanism in GeO2-doped single-mode fibres for temperatures above 20 C. Loss increases at 1.3 and 1.55 ?m are predicted to be less than 0.01 dB km after 20 years.     

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.     

On the effect of vacancies in the silicon and carbon sublattices on the formation of a Schottky barrier at the Metal-SiC interface

The coupling between levels related to silicon and carbon vacancies with metal states is considered in the surface molecule approximation. It is shown that the key role of silicon vacancies in the formation of a Schottky barrier at the Cr-SiC interface is due to the high density of states at the antibonding level.     

1/f noise in the extinction coefficient of an optical fibre

The extinction coefficient, used to express losses in optical fibres due to absorption and diffusion, fluctuates in time with a 1/f spectrum. The authors have measured fluctuations in the intensity of light propagating through optical fibres. Noise measurements as a function of fibre length show that the noise is not due to fluctuations in reflectivity at the ends. The relative noise in the intensity of the transmitted light is proportional to fibre length     

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     

Method for cooling and bubble-free coating of optical fibres at high drawing rates

Limiting factors in the high-rate production of optical fibres are the cooling rate of the glass after drawing and air trapping in the coating. Experiments have proved the possibility of drawing and coating optical fibres at a rate of at least 750 m/min without any bubble formation in the coating. This was realised in a short drawing tower.     

Influence of deep states on CdTe and GaAs metal interface formation

Luminescence and soft x-ray photoemission measurements of clean metal interfaces with (110) surfaces of CdTe from several sources as well as (100) MBE vs (110) LEC GaAs reveal that the quality of the semiconductor can have a major effect on the interface Fermi level stabilization. Crystals with low optical emission from bulk deep levels show reduced state formation at their metal interfaces and improved adherence to the work function model of barrier height. Furthermore, atomic-scale interface chemistry can inhibit the formation of deep traps due to interdiffusion, thereby improving control over barrier formation.     

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.     

Formation of PNx/lnP structure byIn Situ remote plasma processes

In situ remote plasma processes consisting of removal of native oxide due to hydrogen (H₂) plasma, surface modification due to phosphine (PH₃) plasma and deposition of phosphorus nitride (PN_x) films due to decomposition of PH₃ by nitrogen (N₂) plasma have been developed. The insulating PN_x film with optical bandgap of 5.3 eV and electrical resistivity of 3.7× 10¹⁴ Ωcm is obtained by remote plasma chemical vapor deposition. Au/PN_x/InP tunneling metal-insulator-semiconductor (MIS) type Schottky junction is formed by thein situ multiprocess. The effective barrier height is estimated to be as high as 0.83 eV. Enhancement of the effective barrier height is due to both effects of the MIS structure and unpinning of the surface Fermi level.     

Recent progress in microstructured polymer optical fibre fabrication and characterisation

Recent progress in microstructured polymer optical fibre fabrication and characterisation will be presented. A wide range of different optical functionalities can now be obtained by modifications of the microstructure, as is demonstrated by the fibres presented here. Microstructured fibres that are single-mode, highly birefringent or show twin-core coupling are described, in addition to graded-index microstructured fibres and hollow core fibres, the latter case being where light is guided in an air core. Microstructured polymer optical fibres are an exciting new development, offering opportunities to develop fibres for a wide range of applications in telecommunications and optical sensing.