Index profile determination in transition region of optical fibre preform

It is shown that the refractive-index profile in the transition region of an optical fibre preform can be obtained by a combination of a measurement of the deflection function and a ray-tracing procedure.     

Three-dimensional fibre preform profiling

Results are reported of three-dimensional profiling of fibre preforms from deflection function measurements. We demonstrate the importance of performing the integration involved with a sufficient number of points and show how the systematic use of interpolation allows this number of points to be obtained from a few preform projections.     

Measurement of stresses in optical fibre or preform

The stress distribution in the cross-section of an optical fibre or preform is measured based on the principle of the Abel transform. It is also shown that the axial stress component has the same shape as that of the refractive index profile of the preform.     

Holographic measurement of refractive-index profile of optical fibre preform

A holographic method of measuring the refractive-index profile of an optical fibre preform is presented. It uses the principle of shearing interferometry. The method is simple and allows measurements to be repeated even after the preform has been withdrawn for fibre drawing.     

Measurement of stresses in elliptical optical fibre or preform

It is shown that the measurement method used for determining the stress profile in circular optical fibre or preform is directly applicable to the elliptical counterparts with minor modifications in the Abel inversion procedure.     

Nondestructive refractive-index profile measurement of elliptical optical fibre or preform

A nondestructive method of determining the refractive-index profile of an elliptic optical fibre or preform is reported. For the fibre, the pathlength data obtained from interference microscopic measurement are used. For the preform, the ray exit angles are used. These data are put into an integral that can be inverted numerically to obtain the reconstructed profile.     

Relations between moments of index profile and moments of deflection function and phase function of optical fibre or preform

This letter reports the simple relations between the moments of the refractive-index profile and the moments of the corresponding deflection function and phase function of an optical fibre or its preform. These relations enable one to measure the moments of the profile in a simple way. They can also be used for checking the reconstruction errors in the profile inversion program.     

High spatial resolution optical fibre mode profiling

Near-field scanning optical microscopy is used in emission mode to measure the mode profile of singlemode fibre. Excellent agreement is obtained between the mode profile of a singlemode fibre measured using emission and collection modes and qualitative agreement obtained between measurements made on a multimoded fibre and a simple theoretical model.     

New optical fibre fabrication method

A new method for optical fibre fabrication has been found. The method is based on the so-called `sol-gel process?, which enables one to produce a core rod for optical fibre. Pure silica core fibre fabricated using this method exhibits an optical attenuation characteristic as low as 6 dB/km at a wavelength of 0.85 ?m.     

一种应用于激光微烧蚀的光学聚焦系统简化设计方法

针对激光微推力器对光学聚焦系统结构紧凑、聚焦光斑尺寸小以及避免羽流污染的特殊要求,采用传统的光线追迹法研究单透镜直接聚焦、双透镜准直聚焦两种典型方案光学设计方法。针对低功耗半导体激光器光纤耦合输出的芯径和数值孔径条件,在50m级聚焦光斑约束下,研究单透镜聚焦系统设计方案,得到了透镜厚度、焦距、工作距等设计参数的关系;研究准直聚焦光学系统的双透镜系统设计方案,得到了透镜厚度、透镜中心距、工作距等设计参数特征关系。针对两种典型光学设计方案,给出了工程应用设计参数。文中提出的设计方法避免了复杂的光学设计过程,可为激光微推力器激光光束微尺度聚焦提供一种简单实效的方法。     

Inner pressure control method in optical fiber preform fabricationby vapor-phase axial deposition

A method to control inner pressure variation in a vapor-phase axial-deposition (VAD) apparatus is developed. It uses a flame-detection technology to explain temperature fluctuations. Primary causes of the inner pressure fluctuations are analyzed, and suppression techniques are described. They include the adoption of a large buffer-tank and bias gas addition. An inner pressure-feedback control mechanism operates by adjusting the bias gas flow, keeping fluctuations of the inner pressure to less than half of that with no control     

1.55 μm wavelength region high-stability optical fibre lossvariation measurement using fibre coupler

A 1.55 μm-wavelength high-stability optical fibre loss variation measurement system, using a comparison method with an optical fibre coupler, was developed. Long-term stability within ±0.001 dB over a 120 hour period at a room temperature variation of ±2.2°C has been achieved     

Low-OH-content optical fibre fabricated by vapour-phase axial-deposition method

A low-OH-content and long-length optical fibre has been made by the v.a.d. method. The OH content in the rod preform was reduced to about 0.4 p.p.m. utilising the chemical reactions of SOCl2 or CCl4 with OH ions and H2O molecules In the porous glass rod. The minimum loss of the fibre, 20km long, was 1.0±0.1 dB/km at 1.2?m.     

Germanium-oxide glass optical fibre prepared by VAD method

Germanium-oxide glass optical fibre doped with antimony for transmission of the 2 to 3 ?m band has been prepared by the vapour-phase axial deposition (VAD) method. An attenuation loss of 13 dB/km at 2.05 ?m and 70 dB/km at 2.4 ?m has been achieved.     

Simplified laser to fibre coupling via optical fibre up-tapers

A new method for coupling single-mode fibre to laser diodes employing a spherical ruby lens and a single-mode optical fibre up-taper is demonstrated. High coupling efficiency and greatly reduced alignment sensitivities are attained     

光纤剖面折射率分布测量新方法

本文在简述逆几何不迩理论基础上,讨论了如何结合计算机图像处理技术根据光线轨迹得出光媒质的剖面折射率分布方法,并且用在改型干涉显微镜基础上建立的ＣＣＤ摄像显微镜实验装置作出验证,从而也提出一种光纤剖面折射率分布测量的简便,易行,精度可靠的新方法。本文介绍的新方法对如何保证目前已被越来越普遍地应用于光通讯和光纤传感器中光纤性能的主要参数检测有十分显著的意义。     

A filtered-transform scanning microscopic method forrefractive-index profiling of optical waveguides and surface profiling

A new filtered-transform scanning microscopic method that determines nondestructively the parameters that describes the index or surface profiles of optical waveguides is described. The profiling method makes use of the principle of obtaining amplitude and phase information from the intensity pattern of the reflected (or transmitted) beam from an object sample under focused coherent illumination by introducing a spatial filter in the Fourier plane of a microscopic imaging system. The profiling procedure is composed of two steps. In the first step a test pattern is scanned in the reflection mode as a calibration procedure. The test pattern will usually be taken from a steplike phase sample (e.g. metal strips) in which the thickness and widths of the steps have been independently determined. In the second step the test sample is scanned, and the parameters for the profile are determined     

New method of fault detection in optical fibre links

The detection of the signal backscattered by the faults present in an optical fibre is achieved by observing the amplified signal coming out by the rear facet of the exciting laser source. This provides a simple method which employs the same semiconductor laser as a source and an amplifier, thus notably simplifying the procedure for fault detection. Some experimental results are presented.     

High resolution refractive index sensing with cladded multimode tapered optical fibre

A new fibre-optic refractive index sensor is presented. It is based on the radiation losses introduced by the sample medium in a cladded multimode tapered fibre. A simple light transmission measurement setup is used to test some samples. It is demonstrated that the sensor is suitable for measuring RI in the range 1.36 to 1.46, as well as RI changes below 10/sup -4/.     

Determination of refractive index and ellipticity of an unclad elliptical optical fibre

A simple, fast, accurate and nondestructive method of measuring the refractive index and ellipticity of an elliptic optical fibre is presented. This method requires only the measurement of the rainbow angles of the backward scattered patterns of the laser beams parallel to the major and minor axes of the ellipse.