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.     

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.     

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     

Quasi-CW optical bistability in InSb at room temperature

We report the first observation of quasi-steady-state optical bistability in an InSb etalon at room temperature as a result of the generation of free carriers through two photon absorption of 10 μm radiation. Nonlinear tuning of the etalon through two free spectral ranges has been achieved, with bistability observed around the two cavity resonances. Switching from a low to high transmission state has been achieved in times less than 10 ns while switching in the opposite direction occurs within 50-100 ns. The experimental results have been successfully fitted to a numerical model of the device.     

室温选支一氧化碳分子激光器

一氧化碳激光器建立粒子数反转主要是依靠非谐泵浦,在相邻的振转支跃迁上,连续发射波长在5～6微米范围的激光,其中任一振转支的出现与气体温度、谐振腔耦合系数等有密切联系。在通常情况下有十几条谱线同时参与振荡,然而在实际应用上,比如作分子光谱的研究、大气污染检测、泵浦自旋喇曼反转激光器、塞曼效应的研究等需要的往往是具有一定功率水平的单一波长激光,这就需要作所谓选支一氧化碳激光器。目前一氧化碳激光器采用的一种选支办法是将色散元件如光栅或氟化钙棱镜作为构成腔的元件,在单线上获得激光振荡,并且波长可在一定的范围内调节,然而采用这种方法输出的功率和效率将明显减少到未作选支的30％。     

Stability of femtosecond solitons in optical fibres influenced by optical attenuation and bandwidth limited gain

The stability of soliton pulses which undergo the Raman self-frequency shift in the presence of bandwidth limited amplification and loss is examined. General criteria for stable propagation are given which show this behaviour is sensitive to the shape of the gain profile and loss. In particular, stability can only be achieved in a narrow spectral region of the gain.<>     

Two photon induced optical bistability in CdHgTe at room temperature

We report the first observation of quasi-steady state optical bistability in a 360 μm thick, uncoated Cd0.23Hg0.77Te etalon at room temperature as a result of the generation of free carriers through two photon absorption of pulsed 10.6 μm radiation from a hybrid TEA CO2laser (FWHM = 1.75 μs). The experimental results are compared with the predictions of a computer model.     

Wideband optical transmission in smectic liquid crystal lightmodulator at room temperature

Video rate optical transmission at room temperature (RT) for smectic liquid crystal light modulators (SLCLMs) and filter circuits has been demonstrated. The bandwidth of this system has been determined to be 5.6 MHz. Optical transmission of the National Television System Committee (NTSC) video signal at RT has been realised     

Optical loss change caused by hydraulic pressure in multimode optical fibres

The optical loss change caused by hydraulic pressure in a multimode plastic-coated fibre with a buffer layer was examined. The relationship between loss change and fibre dimensions was found. A large-outer-diameter fibre exhibits a small change in the optical loss caused by hydraulic pressure.     

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.     

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.     

Mode attenuation at 1.39 ?m in graded-index fibres

The differential mode attenuation ?m(?) in the spectral region of OH absorption (1.2?1.6 ?m) has been studied in SiO2/GeO2 core graded-index fibres. It was found that the mode attenuation due to OH absorption Km(?) at 1.39 ?m had its maximum in the fibre core centre. The comparison between the calculated and measured Km(?) at this wavelength could be used for the determination of OH-ion distribution profile in optical fibres.     

Post-irradiation formation of Si-SiO2 interface states in a hydrogen atmosphere at room temperature

Si MOSFETs were irradiated with x-rays and then exposed to various partial pressures of H₂ at either room temperature or 125 °C. The number of interface traps and the net positive oxide trapped charged were measured during the hydrogen exposure using spectroscopic charge pumping techniques. During the hydrogen exposure the gate electrode was held at a positive bias to maintain a field of 0.65 MV/cm across the gate oxide. It was found that during the room temperature hydrogen exposure the number of interface traps increased by a factor of about two. The change in the oxide trapped charge during hydrogen exposure indicated that the decrease in the number of positively charged oxide traps was approximately the same as the increase in the number of interface traps. The time evolution and bias dependence of these changes are explained by a model that we previously proposed. In this model positively charged radiation induced defects in the oxide crack the H₂ to form H⁺. Under positive gate bias the H⁺ then drifts to the Si-SiO₂ interface where it forms an interface state, while at the same time removing positive charge from the oxide.     

Dislocations in Si generated by fatigue at room temperature

Dislocations in silicon can be generated in many ways, and they often induce a leakage current at the p–n junction and give rise to data retention failures of the semiconductor devices. In this study, it was found that dislocations could be generated in silicon even at room temperature by fatigue. The dislocations generated in a semiconductor device were investigated by transmission electron microscopy. They formed a cluster 3 μm in diameter, which emerged from the interface between the silicon substrate and a tungsten stud. Most of the dislocations were lying on the (1 1 1) planes. It was discovered that cyclic deformation of the device by ultrasonic vibration during the cleaning process generated these dislocations.     

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.     

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.     

高功率高效率封离式室温CO分子激光器

CO分子激光器是5微米附近连续输出功率最强的激光器之一,它在大气污染探测、分子光谱研究,以及作为诸如自旋反转喇曼激光器泵浦源等方面可望有广泛的应用前景。 CO分子激光器的增益系数随着工作气体温度升高而迅速降低,因此,CO分子激光器通常是采用液氮冷却放电管,或者使用高速流动工作气体的办法来实现激光振荡,获得高功率输出。无疑,这种工作方式对一切实际应用是不方便的。     

Integrated coherent infrared generator operated at room temperature using nonlinear optical waveguide structure

A proposal and the result of the analysis of integrated coherent infrared generator (ICIG) which generates the difference infrared frequency by nonlinear optical mixing in the optical waveguide configuration operated at room temperature are presented. The ICIG has a potentiality of monolithic integration with coherent optical semiconductor sources.     

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.     

基于相位补偿的低温光学系统常温装调方法研究

基于对红外光学系统的热分析,提出一种低温光学系统的常温装调方法.在常温装调时为系统引入额外的相位板来补偿低温系统在常温时产生的离焦和表面变形.通过热分析获得离焦量和表面变形数据,设计出合适的相位板进行补偿,从而可以实现低温光学系统在常温环境下的正常装调和测试.