Automatic determination of refractive index profile of fibers having regular and/or irregular transverse sections considering the refraction of light rays by the fiber

A new model, using non-destructive two- and/or multiple-beam interferometric techniques, is suggested for measuring the refractive index profile of fibers having regular and/or irregular cross-sectional shape taking into consideration the refraction of the light rays by the fiber. The proposed model is applied for three different fibers having different cross-sectional shapes and different refractive index profiles. These fibers are PPT, homogeneous fiber, with circular cross-section, graded index optical fiber of circular cross-sectional shape and Dralon fiber of irregular cross-section. To validate the proposed model it is used, firstly, to calculate the index profile for a standard PPT fiber. Secondly, the calculated results for the irregular Dralon fiber and GR-IN optical fiber are compared with that calculated using other conventional method. From this comparison, we recommend that the refraction must be taken into account to obtain accurate results especially for birefringent fibers and graded index optical fibers.     

A study of the propagation characteristics of W-type single-mode fibers using variational fields of single-clad single-mode fibers

A number of single and two parameter scalar variational fields approximating the fundamental mode of single-clad fibers are available in the literature. The present work aims at checking if these fields can also explain the propagation characteristics of W-type or double-clad single mode fibers with similar accuracies. To assess the accuracies, numerical solution of scalar wave equation is required. A method for solving the scalar wave equation numerically has also been proposed. Investigation shows that the single parameter fields are not very suitable for the W-type fibers. At least a two parameter variational field should be used.     

Formation of fibrous filtering membranes by electrospinning

A technique for production of fibrous materials containing layers of variable-thickness fibers is considered. Membranes in the form of alternating layers of thin and thick fibers are obtained from cellulose acetate and fluoroplastic solutions. The layers of thin fibers specify the filtering properties of the membranes, and those of thick fibers impart them mechanical strength.     

Analysis of circular fibers with an arbitrary index profile by the Galerkin method

We propose a full-vectorial Galerkin method for the analysis of circular symmetric fibers with arbitrary index profiles. A set of orthogonal Laguerre-Gauss functions is used to calculate the dispersion relation and mode fields of TE and TM modes. Examples are given for both standard step-index fibers and Bragg fibers. For standard step-index fiber with low or high index contrast, the Galerkin method agrees well with the analytical results. In the case of the TE mode of a Bragg fiber it agrees well with the asymptotic results.     

A new procedure for analysis of single-mode-fiber far-field data

A new procedure for analysis of far-field data on single-mode fibers is proposed; it allows one to obtain mode field diameters with reproducibility of ±0.05 μm or better and to reconstruct reliably and unambiguously the refractive-index profile even for dispersion-modified fibers with moderate requirements on dynamic range of the measurements.     

Femtosecond spectroscopy of coherent anti-Stokes Raman scattering with frequency-tunable chirped pulses generated in a microstructure fiber

A new scheme of chirped-pulse femtosecond coherent anti-Stokes Raman scattering spectroscopy is proposed and experimentally implemented. A theory of this modification of coherent nonlinear spectroscopy is developed. We use this approach to show that a linear time-frequency mapping defined by linearly chirped pulses allows the spectra of nonlinear response of a medium to be measured by varying the delay time between the pump pulses. Microstructure fibers with a special dispersion profile are at the heart of the experimental implementation of this technique. Such fibers are ideally suited for the generation of frequency-tunable pulses with a smooth envelope and a controlled chirp. We present the results of experimental characterization of the envelope, spectrum, and chirp of anti-Stokes pulses generated in microstructure fibers by femtosecond Cr:forsterite-laser pulses. These frequency-tunable anti-Stokes pulses produced and shaped in microstructure fibers are then employed for coherent anti-Stokes Raman scattering spectroscopy of toluene solution.     

Imaging through a bundle of square cross-section fibers: The dependence of image contrast on the bundle parameters

A very simple formula for the image contrast dependence on the parameters of the imaging bundle of square cross-section fibers is derived for both ideally insulated and cross-talking fibers.     

A new procedure for analysis of single-mode-fiber far-field data

A new procedure for analysis of far-field data on single-mode fibers is proposed; it allows one to obtain mode field diameters with reproducibility of ±0.05 μm or better and to reconstruct reliably and unambiguously the refractive-index profile even for dispersion-modified fibers with moderate requirements on dynamic range of the measurements.     

Imaging through a bundle of square cross-section fibers: The dependence of image contrast on the bundle parameters

A very simple formula for the image contrast dependence on the parameters of the imaging bundle of square cross-section fibers is derived for both ideally insulated and cross-talking fibers.     

双锥光纤模拟理论方法

从双锥光纤的工艺实现和技术应用目的出发,建立了可与实验上易测量的工艺参数相联系的高期型等效双锥光纤模拟理论方法,可用于双锥光纤的制作及光学特性的分析,数值模拟结果与实验符合得很好。     

Coupling methods in prospective single-mode fiber integrated optics systems: A progress report

A review of the research progress on the coupling of fibers to fibers, fibers to thin-film waveguides, and thin-film waveguides to thin-film waveguides is presented here. In general, the direct excitation method is preferred for the coupling of two fibers, with efficiency larger than 90%. The direct excitation method is also preferred for the coupling of two thin-film waveguides and thin-film waveguides to fibers where the two component waveguides have vastly different refractive indices. The coupling efficiency depends on matching the field pattern of component waveguides. The laser source to fiber launching is done mostly by direct excitation. The evanescent field coupling method is preferred for the coupling of two thin-film waveguides that have close refractive index profiles, with efficiency larger than 70%.     

光子晶体光纤非线性特性的研究

光子晶体光纤是近年来出现的一种通常由单一介质构成，并由波长量级的空气孔构成微结构包层的新型光纤．文章介绍了光子晶体光纤的制作工艺、工作原理、基本特性、目前的研究重点和进展情况，重点评述了光子晶体光纤非线性特性方面的研究，特别是在超连续光谱的产生、光孤子效应以及频率变换等方面的实验和理论成果以及潜在的应用．     

Polarization mode dispersion of spun fibers: an analytical solution

A simple analytical solution is derived from coupled-mode theory to describe the evolution of polarization mode dispersion (PMD) in spun fibers. For practical fibers with a beat length greater than a few meters, the solution is valid for a whole category of periodic spin profiles. We find that the PMD change factor is independent of the intrinsic birefringence of the fiber and the fiber PMD scales linearly with the fiber length in the short length regime. This solution allows us to determine phase-matching conditions for spun fibers, in which the PMD evolves periodically along the fiber. An example of determining the phase-matching conditions of sinusoidal-type spin profiles is given.     

Numerical analysis of multicore photonic crystal fibers

A Galerkin's method-based numerical procedure is extended to obtain the modal field distribution of multicore photonic crystal fibers for the first time to our knowledge, which can reveal how the air hole size influences the mode coupling and how the coupling strength varies with wavelength. These results will be helpful in the future design of multicore photonic crystal fibers with proper guidance properties.     

Optical sensing with photonic crystal fibers

A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long‐period gratings and interferometric structures; the fourth one reports applications of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in photonic crystal fibers for sensing.     

纺织纤维光散射特性的模拟与实验

纺织纤维的光散射特性在纺织材料微观结构、光学性质以及无损检测中至关重要。利用纺织纤维各向异性的结构特点改进现有的角谱展开法,得到纺织纤维对倾斜入射平面波的散射以及表征其光散射特性的Mueller矩阵。采用蒙特卡罗算法模拟了平行棉纤维束对倾斜入射偏振光的多次散射,并对其计算结果进行了实验验证。结果表明理论计算和实验测量的散射光斑在形状特征、光强分布上均一致,从而验证了蒙特卡洛方法模拟纺织纤维光散射的正确性。结果同时也表明蒙特卡罗方法在纺织材料光传播特性的理论研究中具有重要的指导意义。     

利用可见光测量近红外单模光纤的模场

光纤的模场分布是光纤最基本的特性,它包含了很多光纤的有关信息,单模光纤都工作在不可见的近红外波长范围内,且在可见光范围并非单模工作。提出了一种利用可见光测量近红外单模光纤模场直径的新方法,导出了一个考虑光纤材料色散的更精确地计算不同V值时模场直径的公式,设计了利用可见光直接拍摄模斑的系统,采用缠绕法提取基模,消除了高阶模对测量结果的影响,利用二元非线性曲面拟合,测得了光纤在近红外工作波长下的模场直径。由于无需红外光源、红外探测器以及精密的扫描装置,该方法具有成本低廉、测量速度快、调整容易等优点。     

Spectroscopic techniques for the forensic analysis of textile fibers

A review has been conducted on the application of the spectroscopic techniques to the comparative study and identification of different textile fibers. Microspectrophotometry in the ultraviolet-visible range and Raman spectroscopy are the main techniques investigated with this aim in the forensic field. UV-Vis MSP is the first recommended technique, which is principally used to study the color of the fibers. A more complete approximation focused on determining the specific color of the fibers providing adding Raman spectroscopy to the analytical scheme. Sometimes, it also provided information about the polymeric nature of the fibers. Regarding FTIR spectroscopy, it is the recommended tool to determine the fiber nature. Raman and FTIR spectroscopy are complementary techniques and a frequent recommendation is a combination of both techniques, in order to get a comprehensive analysis of textile fibers. On the other hand, new and more informative analytical techniques are emerging to the analysis of textile fibers as traces related with criminal contacts, such as infrared chemical imaging spectroscopy and X-ray fluorescence spectroscopy.     

Characterization of the approach to steady state and the steady-state properties of multimode optical fibers using LED excitation

A simple technique has been developed to characterize the approach to steady state and the steady-state properties of multimode fibers using LED excitation. Results are given for 6 mil Selfoc fibers whose far-field pattern for the steady state is in excellent agreement with a calculation by Marcuse. To first order, the steady-state mode distribution fits a simple model of uniform modal excitation of a fiber with a reduced numerical aperture.