基于3D定位的光纤棒内部缺陷检测方法

为检测和定位光纤预制棒的内部缺陷并提高精度,提出一种光线追踪实现3D精确定位的线激光旋转扫描检测方法。利用光散射原理和暗场成像技术,成像设备采集光纤棒每个旋转角纵截面上缺陷的散射光;原始图像经过图像预处理和图像分割获取缺陷的二维信息;基于折射定律和光线追踪建立缺陷的精确定位模型,消除光纤棒表面折射带来的成像位置偏差;最后经过坐标转换、三维建模和三维连通域提取实现缺陷在光纤棒内部的3D定位。实验结果表明:120 W像素的工业相机在旋转角步长为0.9°的条件下,对大尺寸的光纤棒内部缺陷检测轴向定位精度为0.28 mm,径向定位精度为1.05 mm,可实现准确、自动化地检测和定位光纤棒的内部缺陷,为光纤棒的质检和指导光纤拉丝提供重要依据。     

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.     

Design and fabrication of dispersion-managed fibres by periodicetching during the MCVD process

A new design and fabrication method is proposed for a dispersion-managed fibre from a preform prepared by a single session of the modified-chemical-vapour-deposition (MCVD) process. Periodic etching during the MCVD process is used to change the index structure of the preform periodically alone the axial direction. The dispersion measurement of the fabricated prototype fibre shows that desired dispersion management characteristics can be achieved     

Application of focusing method of index profiling to transition region of optical fibre preform

The letter shows how the focusing method of measuring the refractive-index profile of an optical fibre preform can be modified to be applicable to the transition region of the preform. This involves adding a slit between the collimated source and the preform and measuring the scattered power distribution along the projection of the slit in the measurement plane.     

Measurement of refractive-index profile of optical-fibre preform

An experimental system for nondestructive measurement of the refractive-index profile of an optical fibre preform is reported. The result shows that the profile does not significantly change from the preform stage to fibre stage.     

Large graded-index preforms fabricated by high-rate VAD

A large preform for 220 km of fibre was fabricated with the vapour-phase axial deposition (VAD) method. The deposition rate for the core was 1.7 g/min. Optical fibre drawn from a part of the preform had optical attenuation of 0.58 dB/km and bandwidth 500 MHz km0.9 at a wavelength of 1.3 ?m.     

Modified VAD method for optical-fibre fabrication

New techniques for protecting the burner flame and controlling gas pressure in a reaction vessel have been developed for the vapour-phase axial-deposition (VAD) method of soot preform. The growth of soot preform became more stable. It is found that there is a close correlation between the bottom shape of the soot preform and the refractive-index profile of a fibre preform. Optical fibres thus produced indicate improved reproducibility in the bandwidth above 800 MHz km at a wavelength of 0.85 ?m.     

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.     

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.     

Production of single-mode fibres with negligible intrinsic birefringence and polarisation mode dispersion

Spinning the preform during drawing produces a fibre with a permanent twist. It is shown that such a fibre has negligible polarisation birefringence and rotation. Polarisation mode dispersion is similarly reduced.     

Nondestructive measurement of axially nonsymmetric refractive-index distribution of optical fibre preforms

A nondestructive computer-aided measurement of the arbitrary two-dimensional refractive-index distribution of an optical fibre preform is described. The angle of refraction of rays in the preform is measured by an optical set-up which features the use of a triangular mask for converting the angle of rays to their displacement. The index distribution is computed from the information on these refraction angles.     

Extruded singlemode non-silica glass holey optical fibres

The fabrication of the first microstructured singlemode non-silica optical fibre is reported. Extrusion has been used for the first time to produce the microstructured fibre preform. The final drawn fibre has an effectively air-suspended 2 μm core. Singlemode guidance is observed from 633-1500 nm     

26 km-long polarisation-maintaining optical fibre

The letter describes the development of a long-length and large-diameter preform for polarisation-maintaining optical fibres. The preform was 470 mm in length and 48 mm in diameter. As a result, a 26 km-long PANDA fibre is developed. This fibre achieves crosstalk of ?22 dB, corresponding to h = 2.4 × 10-7m-1 and a transmission loss of 0.3 dB/km at a wavelength of 1.56 ?m. These fibres will be useful for future high-speed and medium-span coherent optical communications.     

Stress transformation due to fusion splicing in optical fibre

It is shown experimentally that the frozen-in stress of the fibre is relieved due to fusion joint now reverts to that of the preform with compressive surface stress of the fibre. Consequently, it is expected that the fatigue lifetime of the joint is greater than that of the rest of the fibre.     

New absorption bands in pure and F-doped silica optical fibres

Two very narrow absorption bands positioned at 765 nm and at 1273 nm have been found in pure silica and fluorinedoped silica optical fibres. Their origin is probably connected with the preform production technique. Annealing of the preform and different fibre drawing conditions did not influence the absorption bands.     

Deposition mechanism of fine glass particles and high-rate production of fibre preforms in the VAD process

In order to achieve the high-rate production of fibre preforms, the deposition mechanism in the VAD process has been investigated. The particle deposition rate was found to depend on the Reynolds number of the flame stream. The high-rate preform production of 4.5 g/min was attained by applying this result to the preform fabrication technique.     

Optical losses in soda-lime/silica-cladded fibres produced from composite rods

A method for producing cladded preforms (composite rods) composed of high-purity soda-lime-silica glasses is described. Optical-attenuation measurements have been made on cladded fibres produced from such a preform over the wavelength region 600?1100 nm. Results indicate that the incremental loss in producing a fibre by this technique is very small, and is mainly due to scatter.     

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.     

Reduced loss in extruded soft glass microstructured fibre

The fabrication of small core high-NA soft glass microstructured optical fibres with propagation loss as low as 0.6 dB/m at 1100 nm is reported. Advances in soft glass preform extrusion and fibre fabrication have allowed the first demonstration that extrusion does not significantly contribute to the fibre loss.     

Fabrication and polarising characteristics of D-shaped opticalfibre coated with chromium film

The fabrication process, numerical analysis and polarising characteristics of the D-shaped optical fibre coated with chromium film have been investigated. An optical fibre polariser was fabricated by coating the flat side of the D-shaped fibre, which was obtained by drawing the side-cut D-shaped preform made from the MCVD process, with chromium metal film. The maximum extinction ratio of the fibre polariser was found to be ~55 dB