Compound-glass optical nanowires

A simple method to fabricate nanowires with radii as small as 90 nm from compound-glass fibres is described. Low transmission losses at 1.55 /spl mu/m have been achieved in nanowires fabricated from lead-silicate and bismuth silicate optical fibres.     

Coupling of lasers to single-mode fibres with high efficiency and low optical feedback

A simple automatic method of obtaining tapered ends for single-mode fibres is by using a microcomputer-controlled process. In addition to producing standard tapers of more than 300 ?m in length and radii of curvature of more than 20 ?m at their tip, it is now possible to draw very short and pointed tapers (lengths <200 ?m, radii <10 ?m) resulting in very high launching efficiencies of about 75% with low optical feedback in the laser source.     

In-line optical-fibre filter for wavelength multiplexing

An optical-fibre wavelength-selective directional coupler has been fabricated using evanescent-wave coupling between fibres of dissimilar core radii and refractive-index profiles. This device has a nonperiodic filter response with a bandpass of 90 nm FWHM centred around 1.22 ?m, and has a peak coupling efficiency of 60% with an excess loss of 0.2 dB.     

Coupling tolerances of high-index silicon-oxynitride waveguides with small bending radii

Silicon-oxynitride waveguides gained by plasma-enhanced chemical vapour deposition are very attractive for the fabrication of passive optical components used in optical networks. The low-loss and compact devices with small bending radii are achieved with a new high-index waveguide design. At the same time this feature increases the requirements on the fibre-to-chip coupling compared to common fibre-matched waveguides. In this paper, we discuss the junction of the high-index optical components to fibre systems and their coupling tolerances. The presented solution is based on using high numerical aperture fibres. Furthermore, the option of higher automation and reliability is given by the coupling with tapered fibres because they allow better positioning tolerances.     

非线性发散抛物型梯度折射率棒中的两正交偏振光束

研究非线性发散抛物型梯度折射率棒中两正交偏振高斯光束的传播特性，导出了棒内两光束的束宽半径和波前曲率半径的倒数。     

Generalised Fresnel's law for loss due to curvature

Many rays, predicted by Fresnel's laws to be totally reflected from a curved interface between two dielectric media, are only partially reflected. We derive a generalised Fresnel transmission coefficient to account for this loss. Our transmission coefficient applies to an arbitrary surface; e.g. one defined by two arbitrary radii of curvature. It can be used to determine radiation loss from bent and straight circular optical fibres.     

长周期光纤光栅谐振波漂移规律研究

为了研究长周期光纤光栅纤芯、包层半径及折射率改变时光栅有效折射率和耦合系数的变化规律,采用理论分析与数值模拟相结合的方法,总结出长周期光纤光栅结构参量与透射谱谐振波漂移的关系。结果表明,当光纤结构参量a1,a2,n1和n2增大时,谐振波向短波方向漂移,仅当周期Λ增大时,谐振波才向长波方向漂移。这一结果对设计长周期光纤光栅是有帮助的。     

Theoretical study on modulating group velocity of light in photonic crystal coupled cavity optical waveguide

We present a novel mechanism,which is formed by periodically changing the radii of dielectric rods in the middle row of a photonic crystal,to control and stop light.Using the Bloch theory and coupled-mode theory,the dispersion characteristic of such a photonic crystal coupled cavity optical waveguide is obtained.We also theoretically demonstrate that the group velocity of a light pulse in this system can be modulated by dynamically changing the refractive index or radii of the selected dielectric rods,and the light stopping can be achieved.     

Photosensitivity measurement in optical fibre with Bragg grating interferometers

A new technique based on two low-finesse fibre Bragg grating Fabry-Perot interferometers to study photosensitivity in optical fibre is presented. Phase evaluation using the Fourier spectra allows precise determination of the evolution of the refractive index with accumulated fluence. Results are given for different germanium/boron codoped fibres and for hydrogen-loaded fibres.     

一种基于密度网格索引的k-最近邻查询算法

基于位置的服务的迅速发展对服务响应的效率提升和成本控制提出了更高的要求,本文提出了一种基于密度网格索引的k-最近邻查询算法,该算法首先利用矩形的几何特点获取一系列候选搜索半径,随后根据移动对象的密度分布情况选择适当的候选搜索半径进行距离过滤,尽量减少不必要的内存索引单元和磁盘索引单元的访问.实验表明,实现了本文算法的密度网格索引在k-最近邻查询的查询效率上与ST²B-tree不相上下,而查询的I/O代价与其他索引结构相比有明显的优势.     

Core dopant profiles in weakly fused single-mode fibres

Core dopant profiles have been measured in weakly fused single-mode fibres. The results show that the peak refractive index of the cores decreases and the core size increases during fusing, contrary to previously proposed models. This suggests that the field is still guided by the cores and that the coupling mechanism model should include the effects of the cores for weakly fused fibres     

End launching of, and emission from, leaky modes in graded fibres

It has been established that leaky modes are significant in graded, as well as step-index, fibres. The difficulties of launching bound modes without leaky modes have been mentioned previously, and in this letter the degree of selection that is practicable in fibres with circular symmetric index profiles is described. The results apply equally to output distributions.     

Dispersion-determined limits on production tolerances of single-mode fibres

For single-mode fibres the standard deviation of dispersion at the nominal zero-dispersion wavelength depends strongly on the dispersion slope. For dispersion-shifted fibres, optimum values of the slope as a function of production tolerances on core radius and index difference are found, and for dispersion-flattened fibres maximum allowable production tolerances are given.     

Design tolerances for dispersion flattened SiO2-cladded single mode fibres

It is shown that the dispersion sensitivity to core diameter and to refractive index of the core of ideal broadband-dispersion-compensated single mode fibres can be accurately extracted from optical properties of the cladding material. In SiO2-cladded dispersion flattened fibres, typical sensitivity coefficients are 1.25 ps/km nm and 0.4?0.8 ps/kmnm per percent change in core diameter and core index, respectively.     

Modal dispersion in single-mode fibres: simple approximation issued from mode spot size spectral behaviour

We report a simple and accurate approximation of modal dispersion in single-mode optical fibres deduced from spectral behaviour of mode spot size; neither knowledge of index profile nor of maximum refractive index difference are required in this approximation.     

Propagation in Doubly Clad Single-Mode Fibers

General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters inner cladding/core radii ratio and inner cladding/core index differences ratio. LP01, LP11, and LP02 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 µm.     

Multiquartic approximation in single-mode optical fibres

A new stratification method based on the approximation of the actual index profile of the fibre by means of a set of quartic curves is proposed. The method permits one to deduce accurately the propagation characteristics in the least calculation time, particularly on fibres with nonmonotonic index profiles.     

Robustness Optimization of Fiber Index Profiles for Optical Parametric Amplifiers

Optical fibers with index profiles that are optimized for broadband double pumped parametric amplifiers are thoroughly investigated. The analysis includes random variations in the radii of the profile along the fiber length (introduced in the fabrication process). By optimizing the fourth order dispersion parameter and the effective area we obtain fiber designs that provide flat spectral gain over 200 nm with 3.5 W pump lasers and, at the same time, have robust operation wavelength against fluctuations of up to 1% in the radii of the index profile. These fibers show positive and very small forth order dispersion. Our results indicate that in such low dispersion fibers, the sixth order dispersion parameter must be considered in the optimization algorithm.      

Prediction of modal dispersion in single-mode fibres from spectral behaviour of mode spot size

We report a simple calculation allowing the prediction of the modal dispersion in single-mode optical fibres from the spectral behaviour of the mode spot size and the profile index.     

Leaky ray correction factors for elliptical multimode fibres

Leaky ray attenuation in elliptical graded-index fibres it related to the changes in the ray parameter ? that are induced by fibre ellipticity. Parabolic index fibres are described in detail. Results are given for the correction factors which must be applied to the measured near-field intensity in order to obtain the refractive-index profile.