Determination of the refractive index profile of a symmetric fiber preform by the transport of intensity equation

The refractive index profile of an axially symmetric fiber preform is determined by using the transport of intensity equation. In this method the preform is immersed in an index-matching liquid, and a collimated light beam impinges on it laterally. The intensity distributions of the transmitted light are measured on two close parallel planes inside the preform core. From the recorded intensity distributions, the deflection function is calculated by the transport of intensity equation. The refractive index profile is obtained by means of Abel inversion. Also, for comparison, the refractive index profile of the preform is measured by the focusing method and the results are in agreement with less than 3% error.     

Study on measurement of refractive index profile of GI-POF by light scattering

This paper is devoted to the study on measurement of refractive index profile of graded-index polymer optical fiber (GI-POF) by light scattering. Using Generalized Airy theory and Debye series of an inhomogeneous cylinder, the scattering intensity distributions are obtained of Airy structure of rainbows for different refractive index profile. The results show that positions of Airy peaks depend closely on refractive index profile of GI-POF. Since each order of rainbow penetrates it to different depths, such methods could be used to provide information of the refractive index profile of GI-POF. For GI-POF with given diameter, positions of Airy peaks of rainbows are simulated as a function of refractive index profile, which can be used to inverse unknown parameters of refractive index profile. The least square method is used in inversion of refractive index profile with the given refractive index of the cladding. The results obtained agree with theoretical values with high precision. The method has the advantages of non-instructive and on-line measurement, and can be used for the measurement of other inhomogeneous droplets.     

梯度型聚合物通信光纤制备的理论分析

对直接挤出法制备梯度型聚合物光纤的工艺流程进行了分析,根据双组分混合物折射率计算理论和梯度型聚合物光纤径向折射率分布函数,计算了梯度型聚合物光纤单位长度中所含掺杂剂的质量;将非稳态扩散理论和有限差分法结合起来,对梯度型聚合物光纤折射率分布的形成进行了理论研究,建立了数学物理模型,得到描述梯度型聚合物光纤径向折射率形成的普遍性近似方法.     

Measuring the refractive index of crude oil using a capillary tube interferometer

A method for measuring the refractive index of low-transparent crude oils using a capillary tube interferometer is described. The method is based on analyzing the resulting transverse interference fringe patterns in terms of their positions with respect to the lens/capillary tube interferometer. The refractive indices of seven blended crude oils of low transparency were measured with accuracy of up to six decimal digits and were related to the API gravity of the oils. The ray tracing inside the capillary tube is explained and the transverse bell-shaped interference fringes are interpreted.     

Automatic determination of refractive index profile, sectional area, and shape of fibers having regular and/or irregular transverse sections

A new method based on a mathematical model and a computer program is suggested to determine the refractive index profile of fibers having regular and/or irregular transverse sectional shape. Microinterferogram of both multiple-beam Fizeau fringes and the duplicated image from two-beam interference microscope are used for the determination of refractive index profile, cross-sectional area and shape of three different types of fibers. To confirm the suggested model, the calculated area and the shape of the transverse section of these fibers are compared with those results obtained using conventional methods.     

套管辅助法测量异型预制棒折射率分布

基于光束扫描法的光纤预制棒折射率测试仪主要适用于直径和长度在一定范围内的圆柱形样品折射率分布的测试。提出一种套管辅助法可实现更短长度、更细直径和变直径样品的折射率测试。该方法将待测样品居中放置于一个尺寸符合测试要求的圆柱形套管内,并在套管内注入折射率匹配油,使其没过待测样品后按常规步骤进行测试。对比实验结果表明,套管辅助法与直接测量法的偏差与仪器的测量误差相当。采用套管法,获得了预制棒拉丝终止后变径区不同位置折射率的径向分布,可为拉丝过程的研究提供参考。     

一种动-静态光散射颗粒折射率测量法

提出一种动静态光散射颗粒折射率测量方法.该方法分为三部分,一部分是用动态光散射技术测得颗粒样品的线宽分布函数,然后将此线宽分布连同一组折射率值代入静态光散射公式推算出不同折射率值下的散射光强空间分布;第二部分是用光电探测器测出实际的散射光空间分布;第三部分是将不同折射率下的推算值与实测值做均方偏差运算以做比较,取均方偏差最小时所对应的代入折射率值作为颗粒折射率的最终测量值.此方法对样品的分散度无要求,适用于微米到亚微米级的颗粒物.     

大气气溶胶消光特性和折射率的测量

 介绍了一种综合利用能见度仪、微脉冲激光雷达和光学粒子计数器测量大气气溶胶折射率的新方法。首先使用能见度仪和激光雷达测量出大气气溶胶的消光系数和消光后向散射比，然后使用粒子计数器测量出粒子谱分布，结合气溶胶粒子折射率，根据球形粒子的米（Mie）散射理论，可以得到气溶胶消光系数和消光后向散射比。通过分析消光系数、消光后向散射比、粒子谱分布和折射率之间的关系，结合已知的消光系数和消光后向散射比，反演出大气气溶胶粒子的折射率。     

A refractive index interferometry method based on the X-ray crystallography

The absorption contrast image is very low for those weakly absorbing materials or weak phase object, such as the soft biological tissues, however, the phase item value of refractive index is a thousand larger than the absorption item, therefore the refractive index interferometry method is expected to be a new imaging tool for them. An interferometry method based on the X-ray crystallography is explored to the measurement of refractive index in this paper. The theoretical foundation, the optical design, the crystal transistor performance are the key parts to this interferometry method based on the X-ray crystallography. We give out a special refractive index detection scheme, using a laboratory hard X-ray source, and four single Si crystals. With this instrument, refractive index profile of those weak phase object can be unfolded accurately using this method. This refractive index interferometry method based on the X-ray crystallography will provide a new research tool for those special material properties or biological tissues study.     

色散、群速与群折射率

本文讨论了群折射率存在的物理意义,指出群折射率不仅包含了折射率概念而且还体现了折射率的色散性质,同样能作为材料本身的光学性质参量.接着指出在折射率的白光干涉法测量中存在着忽视色散作用而导致的将群折射率误认为折射率的情况.将群折射率与折射率区别开来,不仅可以消除折射率测量中所存在的错误,而且可以突出色散现象在光传播时间特性上的意义.为此建立了折射率与群折射率的相互变换关系,通过对于典型物质的折射率与群折射率变换关系的计算,说明二者在数值上的差别甚至对于气体介质来说也是不能忽略的.     

变折射率介质中光线追迹通用算法的研究

基于几何光学的光线折射和反射原理提出了变折射率介质中的光线追迹算法,给出了在光线追迹过程中进行递推的反射光线和折射光线的方向余弦方程;解决了空间中法线的确定和光线回转等问题。最后通过对多种不同的存在解析解的特殊折射率分布的数值解值和解析解值的比较,验证了算法的正确性,并且讨论了应用算法时应该注意的问题和算法中还有待解决的问题。该算法不但具有广泛的适用性,基本不受折射率分布的制约,而且其数值解精度达10^-5。该算法在变折射率介质的光学设计和空间成像补偿等方面有着广阔的应用前景。     

使用红外干涉仪测量红外材料折射率

使用自行研制的泰曼型红外干涉仪测量红外材料的折射率.在干涉仪的测试臂中加一个旋转台,将被测件放在旋转台上旋转,在旋转过程中经过被测件的光程发生改变,导致干涉条纹发生移动,通过测量条纹的移动数和被测件的旋转角度来计算出被测件的折射率.测量结果显示,25 °C时在10.6 μm波段处锗单晶的折射率为4.003,硫系玻璃锗砷硒（GeAsSe）的折射率为2.494.折射率测量的误差在10－3量级,增加被测件的厚度会进一步提高折射率的测量准确度,待测红外材料的折射率越低,测量准确度越高.     

Measurement of refractive index change induced by dark reaction of photopolymer with digital holographic quantitative phase microscopy

Light-induced refractive index change in photopolymer is quantified by a digital holographic microscope. The refractive index change is induced as the dark reaction which proceeds inside the photopolymer after a writing beam is stopped. Time-lapse phase distribution across the photopolymer is measured by the off-axis digital holographic microscope which enables us to retrieve the 2-D phase map from a single hologram. It is found that the initial phase profile does not coincide with the illumination intensity distribution. This observation suggests that the rate of the refractive index change in dark reaction is not proportional to the illumination intensity in case the exposure energy becomes high.     

Measurement of refractive index homogeneity of parallel optical component

In this paper, we present a method for enhancing the measurement capability of refractive index homogeneity for parallel optical components, which phase-shifting interferometry cannot handle with. With the help of wavelength-modulation phase-shifting interferometry, a series of multiple-surface interference fringes are obtained and analyzed by Fourier transform. Based on the fact that the interference fringe corresponding to each interference cavity has its own variation frequency, the wavefront aberrations induced by each interference cavity are obtained and the refractive index homogeneity is then obtained. It is proved by experiment that the enhanced method can measure the refractive index homogeneity of parallel optical components more accurately and conveniently compared with the traditional measurement approach. Therefore, it will have potential application forwards in optical measurement field.     

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.     

一种适用于任意折射率分布的等效折射率方法

提出了一种新的等效折射率方法,可以将光波导的两维折射率分布精确等效成一维折射率分布。从波动方程出发,通过严格的数学推导,得到了一维等效折射率分布的表达式。该等效折射率分布由二维光波导的模场分布和折射率分布决定。在此等效过程中,几乎无任何近似,因此具有比传统等效折射率方法(EIM)更高的精度,而且不受波导截止条件的限制,并适用于任意的折射率分布结构。以SOI(silicon-on-insulator)脊型光波导为例,给出新方法的一个具体等效实施过程,比较了新方法与传统等效折射率方法计算得到的等效模场分布及等效折射率,结果显示本文方法的有更高的计算精度。最后,文中给出了一个利用这种等效方法计算弯曲波导损耗的例子。新方法可以使对三维结构(截面为任意折射率分布)的模拟简化成二维模拟。     

Measurement of gradient refractive index profile of crystalline lens of fisheye in vivo using optical coherence tomography

We report the use of optical coherence tomography (OCT) for noninvasive measurement of the refractive index profile of a crystalline lens of a fisheye. The approach exploits the fact that OCT provides a direct measurement of the optical path of the light traveled through the medium. The gradient refractive index profile for the crystalline lens was retrieved by iterative fitting of the optical path calculated by the ray tracing method with that experimentally measured using OCT. The estimated error in refractive index is approximately 1%. The measured gradient refractive index and Matthiessen’s ratio (ratio of focal length to lens radius) are in good agreement with the previously reported values. PACS 42.62.Be; 42.30.-d; 42.30.Wb; 07.60.Vg     

K-Na离子交换单模平面波导的制备及其表征

通过K-Na离子交换技术制备了多模玻璃平面波导.采用棱镜耦合技术测量了波导的有效折射率,用IWKB方法拟合得到K-Na离子交换波导的折射率分布符合高斯分布,由色散曲线得到单模波导的制备条件(即扩散深度范围),从而得出单模波导的离子交换时间范围,制备出单模波导,并通过求解WKB色散方程得出单模波导的表面折射率.用普通数码相机,通过对离子交换平面玻璃光波导传输线进行数字成像,根据传输线上的光强分布拟合出光强传输衰减曲线,计算出单模波导的传输损耗大约为0.4 dB/cm.     

聚焦法测量塑料光纤折射率分布的可行性研究

结合理论分析和实验验证,探讨了聚焦法测量塑料光纤纤芯的折射率分布的可行性。结果表明,对GI-POF而言,聚焦法是一种简单可行的技术.但是对SI-POF,由于入射光线在光纤边界处发生交叉,聚焦法不能精确测量其折射率分布.     

Mode field distribution of an integrated-optical waveguide generated by UV-laser radiation at the surface of a planar polymer chip

An integrated-optical strip-waveguide is directly written into the surface of a planar polymer substrate by an excimer laser beam. The mode field distribution, the surface refractive index and the refractive index depth profile of the waveguide have been examined. The intensity distribution of the mode field strongly depends on the refractive index depth profile, on the light coupling conditions and on the waveguide fabrication process parameters.