光纤环相干性分析

运用部分相干光理论,得到了光纤环自相关函数,并利用自相关函数推导出了光谱透射因子,它把光纤环输入、输出光场的光谱密度函数直接联系起来,代表了光纤环的相干性.应用光谱透过因子,结合光纤环耦合输出系数、光学长度、损耗分析讨论了光纤环相干性.     

光纤环光谱传递函数

根据部分相干光理论,得到了光纤环光谱传递函数。并分析了光纤环光学长度、耦合输出系数、损耗对光纤环光谱传递函数的作用。     

光纤弯曲对干涉式光纤陀螺性能的影响

为研究光纤弯曲对干涉式光纤陀螺性能的影响,选取常用的单模光纤、保偏光纤、光子晶体光纤及保偏光子晶体光纤为研究对象,建立了光纤弯曲与光纤陀螺性能的相关理论模型。以高精度光纤陀螺应用为背景,选取掺铒超荧光光纤光源,改变光纤弯曲半径,测出了经过光纤样品后的光功率、平均波长、光谱宽度的变化和平均波长波动,在此基础上分析了弯曲半径对光纤陀螺标度因数和随机游走系数的影响。理论分析和实验结果表明,采用光子晶体光纤时,光纤弯曲对光纤陀螺性能几乎没有影响,采用其他光纤时,需要严格控制光路中的光纤弯曲半径。     

光纤转动引起光纤光谱效率变化与改正

光纤的焦比退化(focal ratio degradation)是光纤光谱效率损失的重要原因之一。光纤在安装和每次定位过程中,光纤的转动和扭曲会引起光纤焦比退化发生变化,从而改变光纤的传输效率,每根光纤由此造成的传输效率变化都会存在差异。而这样的效率差异无法用通常天文观测中使用的晨昏天光平场或者圆顶平场改正。减天光是光纤光谱数据处理中决定光谱质量的重要环节。减天光处理要求对不同光纤的传输效率进行归一化处理,以扣除不同光纤之间传输效率差异导致的天光背景测量的误差。对于与天光背景亮度接近乃至更暗的观测目标而言,光纤传输效率的改正精度决定了减天光的精度。测试了LAMOST望远镜光纤转动对光纤传输效率的影响情况。在检查了光谱中天光发射线强度与光纤传输效率的关系,和验证了光纤效率变化与波长变化相对独立的基础上,提出并且证实了通过测量各光纤中天光发射线强度作为光纤相对效率变化量来改正光纤效率差异的方法是可行的。这种方法已经被应用到LAMOST二维光谱处理当中。     

液芯光纤光谱仪

液芯光纤可以使拉曼光谱强度提高103倍。将液芯光纤既作为样品池又作为前置放大系统,研制成功了体积小、重量轻、成本低、灵敏度高的小型拉曼光谱仪。结果表明:通过对液体及溶在液体中的样品进行自发拉曼光谱、共振拉曼光谱的测量,获得了理想的拉曼光谱。     

光纤化学传感技术研究近况

光纤化学传感器作为传感器的一个重要分支,结合了化学和光学的相关技术,将化学制膜、光纤技术以及化学分析中的分光光度法、拉曼光谱、荧光光谱、折射率检测等方法相融合,以其微型化,抗电磁干扰,传输信息量大,拥有自身参比等特点不断向前发展。简要综述了光纤化学传感技术研究近况和未来的发展趋势。重点对光纤pH化学传感器、光纤离子化学传感器和光纤气体化学传感器进行了介绍。简要分析了常见的敏感膜制备方法如化学键合法和溶胶凝胶(sol-gel)等方法。新型光纤——微结构光纤的出现为光纤化学传感器开辟了新的发展方向。由于其具有大的内表面积,结构设计灵活多样,光纤内部提供感应场所等特点,快速度成为光纤化学传感器的重要发展方向和研究热点。对微结构光纤衍生而来的新型光纤化学传感器进行了详细评述, 最后对光纤化学传感器的未来进行展望。     

塑料光纤拉曼散射的研究

给出了聚甲基丙烯酸甲脂(PMMA)塑料光纤(POF)的一级受激拉曼散射光谱,研究了一级斯托克斯光谱特点,测试了它的阈值,带宽,分析了拉曼光谱的形成机制,并将塑料光纤的拉曼光谱和石英光纤的拉曼光谱进行了比较。     

国产中红外光纤的研制及其应用研究

中红外光纤与红外光谱仪联用能够用于原位、远距离和在体的无创检测。对国产中红外光纤进行改装 ,对光纤的导光性能和用于测定进行研究。采用新的设计 ,研制出单根裸光纤可减少能量损耗 ,使得光谱信噪比提高。对水、乙醇体系以及肿瘤样品进行了光谱测定 ,得到了比较好的结果 ,表明国产光纤可以用于一般样品及生物样品的检测。     

光纤腔衰荡光谱技术及其最新进展

阐述了腔衰荡光谱技术的基本原理及应用;从结构设计的角度考虑,归纳出光纤衰荡腔的三种基本结构,并对光纤腔衰荡光谱技术及其最新进展进行了评述;报道了我们采用脉冲光纤环衰荡光谱技术进行液体检测取得的最新进展;在总结光纤腔衰荡光谱技术优点的基础上,展望了其发展前景.     

液芯光纤喇曼光谱的研究

本文叙述了利用液芯光纤技术获得最佳自发喇曼光谱的方法和条件。用16mW He-Ne激束为泵光浦源,获得了较高强度的溴苯自发喇曼光谱。首次用测量喇曼信号强度的方法,计算出光纤衰损系数α,从而获得了最大喇曼光谱所对应的最佳光纤长度。本文以15OmW Ar离子(488nm)激光器为光源,用Spex1403喇曼系统,得到了丰富的溴苯喇曼光谱,比用普通方法获得的喇曼光谱强度高两个数量级。实验结果与理论计算基本符合。     

Transmission properties of all-silica fibres for high-power Nd:YAG lasers

The transmission properties of two different types of all-silica fibres, step index and graded-index fibres, are investigated using a multimode high-power cw Nd:YAG rod laser. The reflections from the fibre surface back into the laser cavity affect the laser power and the beam parameters, waist diameter and divergence. A set-up for simultaneously measuring these values in front of and behind a fibre is presented. The maximum laser power transmitted by fibres is dependent upon the beam parameters, the fibre design and the surface conditions. An upper limit for the maximum divergence which can be coupled into a fibre with a certain numerical aperture without loss is given. The beam parameters behind the fibre, related to the input parameters, are presented.     

Ultrasonic characterization of ceramic fibres at ambient and elevated temperatures

A non-destructive laser-generated ultrasonic inspection system has been developed to evaluate the elastic properties of ceramic fibres. The approach uses a pulsed Nd:YAG laser to excite ultrasonic signals in fibres. The signal is detected by a piezoelectric acoustic emission transducer to obtain the appropriate frequency response suitable for an elastically one-dimensional sample. By using a differential time-of-flight system, a very accurate measure of the velocity can be obtained in the fibre, with a total scatter of less than 0.5%. This approach has been used to investigate the Young's modulus of polycrystalline carbon and boron fibres as a function of stress. Both types of fibres were found to have a Young's modulus increase as greater applied loads were imposed. The carbon and boron fibres, along with silicon carbide fibres, were evaluated at elevated temperatures up to 700 °C. The carbon fibres were found to have an immediate decrease in the Young's modulus as the temperature was increased, due to oxidation of the carbon. The Young's modulus of the boron fibres decreased only at temperatures higher than 200 °C, probably the result of a microstructural transformation or relaxation. The silicon carbide fibres were found to have no significant change in the elastic properties up to 700 °C. The ultrasonic technique was also applied to polycrystalline alumina fibres and fibre tows between ambient temperature and 1200 °C in a specially designed furnace. Using this technique, it was possible to distinguish the changes in the elasticity of the alumina fibres as they were processed into -alumina. The change in the Young's modulus was readily apparent during phase transformations to -alumina. In addition, the ultrasonic velocity can be used to infer information concerning any coatings that were applied to the alumina fibres. This can be used to aid in the quantification of the coating thickness and uniformity. The application of the ultrasonic inspection system has demonstrated the ability to determine rapidly and non-destructively the elastic properties in ceramic fibres. The information gained from the measurements can be used as a quality assurance technique, or can be modified to be a real-time process control/process monitoring system.     

Modal characteristics of few-mode silica-based photonic crystal fibres

The modal characteristics of silica-based photonic crystal fibres (PCF) are examined through a scalar modal analysis combined with an effective V-parameter model using a finite-difference method. Cut off frequencies of the lowest-order modes and the normalised dispersion curves are given and are found to be quasi-independent of the hole-size-to-pitch ratio. A simple and accurate empirical relation for the cutoff wavelength is given for the first higher-order mode for fibres with hole-size-to-pitch ratio below 0.7. These results should be very useful in designing PCF's for various applications.     

Twin-hollow-core optical fibres

Twin-hollow-core microstructured optical fibres have been fabricated and characterised for the first time. The fibre cladding structure results in guidance by the inhibited coupling mechanism, in which there is a low overlap between the core modes and surrounding structure. This results in minimal interaction between the modes of each core in the transmission bands of the fibre and hence minimal coupling between the cores. It is shown that light is able to couple between the cores via coupling to cladding struts in the high loss wavelength bands.     

Assessment of dicumyl peroxide ability to improve adhesion between polylactide and flax or hemp fibres

Dicumyl peroxide (DCP) is commonly applied as a cross-linking agent in polymer processing. The main aim of this work was to assess the ability of DCP to improve adhesion between polylactide (PLA) and flax or hemp fibres by their interphase cross-linking. Short fibre-reinforced PLA composites were manufactured due to the importance of short fibres in injection moulding of high-quality biocomposites. Reactive extrusion of the PLA, flax or hemp fibres, and DCP was performed. The flax or hemp fibre content was 10?wt%, while DCP varied with 0.5 and 2.5?wt%. The fibres and PLA were mechanically mixed, extruded, granulated and injection moulded to form samples for testing. The samples were characterized by differential scanning calorimetry (DSC), tensile and impact strength tests, dynamic mechanical analysis and scanning electron microscopy (SEM). It was found that flax and hemp fibres increased the Young’s modulus while these fibres decreased the impact strength. Addition of DCP led to increase in PLA crystallinity at the interface with fibres which led to further decrease in impact strength. For that reason, it was concluded that DCP is an ineffective agent to improve interphase adhesion between PLA and short flax or hemp fibres.     

Automatic fringe analysis of two-beam interference patterns for measurement of refractive index and birefringence profiles of fibres

Automatic fringe pattern analysis is a powerful and inexpensive digital image-processing technique. Two-beam polarizing interference Pluta microscope [Pluta M. Opt Acta 1971;18:661, Pluta M. J Microsc 1972;96:309] is automated by the computer-aid via CCD camera and digital frame grabber. Software program is prepared to deal with the duplicated (separated and overlapped) Microinterferograms produced by two-beam polarizing microscope. It also gives an accurate and fast automatic measurement of refractive index and birefringence profiles for fibres. In this paper, the refractive index and birefringence profiles of two different types of fibres, basalt and polypropylene (PP) fibres are presented. A new method to determine the birefringence profile of fibres from non-duplicated microinterferogram is suggested. The cold drawing process for PP fibres is studied.     

Evaluation of splice loss in single-mode graded index fibres by a simple technique

We present simple and accurate analytical expressions for the evaluation of splice loss in single-mode graded index fibres. Our analysis is based on simple series expression for fundamental mode of such fibres which we have developed recently. Since splices are highly tolerant for longitudinal separation, we restrict our analysis to cases of transverse offset and angular tilt only. The concerned calculations require much less computations. With examples of step and parabolic index fibres, we show that our predictions agree excellently with the exact results. A useful collection of integration and differentiation formulae involving Bessel functions is presented in the appendix for ready reference to engineering problems of similar computational context.     

Origin of the variability of the mechanical properties of silk fibres: 1 ‐ The relationship between disorder,hydration and stress/strain behaviour

The causes of the variability in mechanical behaviour of various silks obtained from silkworms (Bombyx mori, Antheraea/Tussah) and spiders (Nephila madagascarensis) have been studied by tensile uniaxial tests, differential scanning calorimetry and Raman microspectrometry. Analyses of tensile stress–strain curves recorded for different silkworm and spider baves and single fibres, undergoing different histories (age, degumming, thermal/chemical treatments), allow the behaviour to be classified into five groups and correlated with the fibroin/spidroin structural status: (1) Type I exhibits linear elastic behaviour and then a quasi plateau, (2) Type II has a two‐step linear elastic behaviour with kinks then a quasi plateau, (3) Type III exhibits a smooth transition from a linear behaviour to a plateau, (4) Type IV has a behaviour rather similar to that of Type I but above ~8–12% hardening occurs, and (5) Type V results in the breakage of fibres during the first elastic stage. Unambiguously, Type IV is more frequent for degummed, very dried fibres and Type III for water‐saturated fibres. The most striking Raman signature differences are observed in the Raman intensity of the amorphous/‘ordered’ νN–H and H₂O band components and correlated to the water content and disorder degree according to the calorimetry study. Types I and II are frequently observed for fresh (largely amorphous) spun fibres/baves. Type V is characteristic of degraded fibres. Type IV represents the most ordered state. The similar stress–strain types for dried silkworm and spider fibres show that the general difference in amino acid contents is not the most pertinent parameter for the mechanical behaviour. Copyright © 2011 John Wiley & Sons, Ltd.     

Light propagation in multi‐step index optical fibres

This paper reviews the theoretical analysis of light propagation we have carried out on multimode multi‐step index (MSI) optical fibres. Starting from the Eikonal equation, we derive the analytical expressions that allow calculating the ray trajectories inside these fibres. We also analyse the effects of leaky rays on the transmission properties of MSI fibres. For this purpose, a single analytical expression for the evaluation of the ray power transmission coefficient is calculated. Afterwards, we investigate the effects of extrinsic and intrinsic coupling losses on the performance of MSI fibres, providing analytical expressions to calculate the coupling loss and, also, determining the most critical parameters. Finally, we carry out a comprehensive numerical analysis of the fibre bandwidth under different source configurations.     

Origin of the variability of the mechanical properties of silk fibres: 2 The nanomechanics of single silkworm and spider fibres

The variability in mechanical stress–strain behaviour of various silks obtained from Bombyx mori silkworm and Nephila madagascarensis spider fibres has been studied by high resolution Raman analysis using the Raman shift induced by application of a controlled strain on the νN–H mode as a probe. Silk fibres exhibiting typical 1, 2, 3 and 4 Types have been selected from their characteristic tensile stress–strain behaviour. A perfect relationship between the nanomechanic (at the scale of the chemical bond) and macroscopic (silk single fibre) behaviour is observed as in the case of other polyamide fibres (natural keratin and synthetic PA66). Copyright © 2012 John Wiley & Sons, Ltd.