利用偏振光控制的光学转换新方法

报道了一种新的非相干-相干光学转换方法,该方法利用了偏振光对含偶氮材料中自衍射的增强和抑制作用,所用样品为具有较大光致双折射(δ_n=1.3×10^-2)的偶氮掺杂聚合物薄膜.研究结果表明,当泵浦光偏振方向与两束记录光垂直/平行时,衍射效率得到了极大的增强/抑制.本文通过改变泵浦光的偏振方向得到了入射非相干图象的正片和负片.     

衍射透镜的精确设计方法

根据光线在基板和衍射层中实际光路作者导出了衍射透镜的精确设计计算公式,基于这种公式设计出的微透镜的成象质量优于基于简化公式设计的衍射透镜.本文介绍这些严密的设计公式和设计过程,给出了工作波长λ=0.6328μm、直径2R=300μm、基板(折射率ns=1.51)厚1000μm、衍射层折射率nd=1.56的微透镜设计面形以及象点的能量分布.     

二元衍射光栅式偏光器件的设计

本文利用双折射晶体刻划成的二元衍射光栅的衍射偏振特性,设计了偏光器件(可分别对o光或e光起偏);偏光分束器件(包括非对称及对称偏振分束两类),并对有关参数对设计的影响进行了讨论.     

菲涅耳型衍射光学元件的研究

本文在衍射理论基础上,深入分析了菲涅耳型衍射光学元件的特性,针对连续及二元浮雕结构,建立了位相深度因子(M),波长匹配系数(α)与衍射效率的关系式,对影响衍射效率的因素进行了讨论.研究了设计与工艺的匹配问题,建立了数值孔径,最小特征尺寸与衍射效率的关系,为不同波段衍射光学元件的应用,及设计和评价衍射光学元件提供了有效的理论方法.本文最后举例分析了用于白光波前传感器中的小数值孔径微透镜列阵的性能,并对衍射效率及传递函数两个综合指标进行了测量.     

一种设计二元衍射元件的优化方法

基于菲涅耳衍射原理和Gerchberg-Saxton的迭代算法,提出一种孔径分区设计二元衍射元件的优化方法.采用此方法设计的二元衍射元件产生的目标光强于输入激光的模式是不敏感的.具体设计与研制了用于CO₂激光表面(火卒)火处理的二元衍射元件,该衍射元件使CO₂激光束变形成12mm×2mm的矩形光斑.试验结果表明,产生的目标光斑满足设计要求.     

偏振和衍射双重效应影响的Schmidt棱镜特性

一束偏振光经过Schmidt棱镜的两个不同路径,成为两个不同的偏振状态,使得出射光束的偏振态呈现非均匀分布.为了探索偏振态非均匀分布对Schmidt棱镜传光质量的影响机理,将两个路径对应的光波函数引入屋脊衍射积分方程,得到了偏振效应影响的屋脊衍射场强分布.场强分布的数字计算表明:在偏振效应和衍射效应的双重影响下,经Schmidt棱镜出射的光场分布出现了严重变形;对应同一入射线偏振光出现的P、S两分量位相差的差异,使得P、S分量的屋脊衍射光强分布I_P、I_S有很大差异,这种差异在入射线偏振光方位角为0°和90°时达到最大;而合光波的衍射光强I_P+I_S是分裂为有一定空间间距的多峰分布,但多峰分布随入射线偏振光方位角的变化比较小.实验拍摄了He-Ne激光经Schmidt棱镜衍射后出射光强分布图.实验结果和理论分析一致性表明:Schmidt棱镜中的偏振效应和屋脊衍射效应导致了一束入射线偏振光分裂为有一定空间间距的多峰光束,严重破坏了Schmidt棱镜的传光特性.     

抗癌药物铂络合物构效关系的物理方法研究

本文用X射线衍射、傅里叶变换红外光谱、差热分析等物理方法研究了抗癌药物铂络合物特性、结构以及构效关系。研究结果表明:cis-[Pt(NH₃)₂Cl₂]属简单斜方晶系,晶格常数a=0.9221nm,b=0.8771nm,c=0.6890nm.草酸二氨合铂的结构为斜方晶系,其晶格常数为:a₁=1.0721nm,a₂=0.6402nm,a₃=1.8570nm,并用傅里叶变换红外光谱、差热分析、元素分析等方法对它们理化特性进行了研究.     

体积全息衍射效率的分析

本文指出对于通过折射率变化来实现相位调制的全息图(无论是漂白后的银盐干版,或DCG版),在通常情况下其相位调制度都较小,不可能发生过调制现象,故拍摄参数选择范围相对较宽。要获得高衍射效率全息照片的关健应放在如何提高干涉项引起的相位调制折射率n₁上。本文还指出当反射全息处於弱布喇格衍射的情况下,再现图象的单色性下降,并存在透射象。     

LiBX2 (B=Ga, In; X= S, Se, Te)光学性质与力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了LiBX₂ (B= Ga, In; X= S,Se,Te) 晶体的光学性质与力学性质. 由禁带宽度推断出晶体抗激光损伤阈值的大小顺序为LiGaS₂ > LiInS₂ > LiGaSe₂ > LiInSe₂ > LiGaTe₂ > LiInTe₂. 六种晶体在常压下均满足机械力学稳定性要求, 且铟化合物可塑性及延展性强于镓化合物. 这些晶体的静态电介电常数 ε₁(0)、静态折射率n(0)和双折射率Δn 理论计算值与实验值相符. LiGaS₂, LiInS₂, LiGaSe₂, LiInSe₂和LiGaTe₂五种化合物双折射率较高, 并且它们的吸收谱与反射谱在中远红外区是透过的, 因此可推断出这五种化合物可以成为优异的中远红外非线性光学材料.     

基于等离子体增强化学气相沉积技术的光电子器件多层抗反膜的设计和制作

针对光电子器件端面抗反镀膜的要求,研究了基于等离子体增强化学气相沉积(PECVD)技术的多层抗反膜的设计和制作.首先,对影响SiN_x折射率的因素进行了实验研究,确定了具有大折射率差的SiO₂/SiN_x材料的PECVD沉积条件.根据理论计算分析,设计了四层SiO₂/SiN_x抗反膜结构,能够在70 nm的波长范围内实现低于10^-4的反射率     

Numerical analysis of plasmon polarition refractive index fiber sensors with hollow core and a long period grating

The main principle of this design is based on the efficient energy transfer between the waveguide mode (WM) and the co-directional SPP provided by a properly designed fiber long period grating (LPG). This LPG is imprinted into a waveguide fiber layer of a specially designed hollow core optical fiber. The simulations are based on the finite element method (FEM) algorithm in electromagnetics and coupled mode theory for gratings. Compared to the previous proposed structure using a fiber Bragg grating (FBG), this novel kind of sensor can greatly enhance the refractive index sensitivity, e.g., from 5.93 nm/RIU (with FBG) to 817 nm/RIU (with LPG) at the sensing refractive index of 1.40. The other advantage is that the working conditions can be performed for the well-developed telecom wavelength windows 1500-1600 nm.     

Investigation of Grating Growth Characteristics in Planar Lightwave Circuits for External Cavity Laser

We fabricated Bragg gratings in planar lightwave circuits and investigated their growth characteristics. The refractive index modulation of the gratings grew in the PLC with total fluence F by the power law δ n = AF^B with A = 8.6 ± 0.9 × 10^-8 and B = 1.47 ± 0.02. The PLC gratings as external reflectors for ECLs were controlled reasonably well by adjusting the writing conditions based on the power law and the coupled mode theory. The properties of fabricated PLC gratings were closely matched to the design parameters of the PLC grating. The single longitudinal mode oscillations of the ECLs were also demonstrated at 1309.5 nm and 1550.5 nm.     

Special Report: High-Speed Access Report—Third Quarter 2010

Abstract

We fabricated Bragg gratings in planar lightwave circuits and investigated their growth characteristics. The refractive index modulation of the gratings grew in the PLC with total fluence F by the power law δ n = AF ^B with A = 8.6 ± 0.9 × 10^?8 and B = 1.47 ± 0.02. The PLC gratings as external reflectors for ECLs were controlled reasonably well by adjusting the writing conditions based on the power law and the coupled mode theory. The properties of fabricated PLC gratings were closely matched to the design parameters of the PLC grating. The single longitudinal mode oscillations of the ECLs were also demonstrated at 1309.5 nm and 1550.5 nm.     

基于长周期光栅的有机聚合物高速电光调制器

结合长周期光栅的特性和有机聚合物的优点,首次提出了一种新型的基于长周期光栅的有机聚合物高速电光调制器结构。应用多层光波导理论,分析计算了聚合物折射系数变化与长周期光栅谐振波长的关系。在此基础上进行了模拟实验,结果表明理论分析与实验基本一致。     

Filtering characteristics of film-coated long-period fiber gratings operating at the phase-matching turning point

We present novel filtering characteristics of film-coated long-period fiber gratings (LPFGs) operating at phase-matching turning point (PMTP). The 3 dB bandwidth of a single broadband dip depends greatly on the film refractive index and thickness. A π-phase-shift in the grating center produces two band-rejection peaks between which the separation reaches 375 nm. This separation increases with the number M (M > 1) of π-phase-shifts that divide the LPFG uniformly. The central loss is constant at zero for odd M, whereas decreases with M for even M. Increasing film thickness and refractive index result in blue shifts of the dual peaks and enlarge the separations, which exhibits excellent tunabilities.     

OCT图像法测量折射率

基于光程匹配原理提出了一种用光学相干断层成像(OCT)系统获得的图像测量样品折射率的方法。通过分析光程匹配原理,给出用OCT图像法测量样品折射率的原理及过程。以玻璃载波片和黄瓜组织为样品进行实验。实验结果表明,用OCT图像法获得的载玻片和黄瓜组织的折射率测量值分别为1.499和1.353,与发表或已知的折射率结果相吻合,测试结果的随机误差可小于0.01。另外,使用OCT图像法通过短时间所采集的两幅图像可对横向扫描任意位置的折射率同时进行测量。该方法进一步简化了基于光程匹配原理的折射率测量法的过程,缩短了测量时间,是一种快速测量样品折射率的实用方法。     

Novel high-quality Fano resonance based on metal-insulator-metal waveguide with L-shaped resonators

Developing a convenient method that can be routinely applied for ascertaining proportions of different vegetable oils employed in commercial blended edible oils remains a significant challenge. We address this issue by proposing a novel method for detecting volume fraction of different oils based on the fact that these oils are optically transparent and have slightly different indices of refraction at a given temperature and wavelength. Accordingly, we develop a highly sensitive sensor for measuring the index of refraction of oil blends based on Fano resonance spectra obtained using a metal-insulatormetal(MIM) waveguide structure comprising a gapped straight waveguide coupled with two L-shaped resonators. The index of refraction sensitivity and figure of merit of the structure are calculated based on modeling using the finite element method, and the waveguide structure is accordingly optimized by adjusting the different geometric parameters to achieve a high-quality Fano resonance spectrum. The optimized structure achieves an ultra-high refractive index sensitivity of 770 nm/RIU in terms of a refractive index unit(RIU) of 1. Moreover, a highly stable linear relationship is obtained between the refractive index of mixed edible oils and the resonance wavelength. Experimental results demonstrate that the proposed structure can detect slight changes in the volume fractions of the components in blended oils.     

Deposition of coatings on long-period fiber gratings: tunnel effect analogy

The sensitivity of Long-period fiber gratings (LPFGs), coated with high-refractive-index thin film overlays, to the refractive index and the thickness of the overlay, and to the ambient refractive index, can be enhanced with a design based on a two-overlay coating of an LPFG. The first overlay of lower refractive index than the cladding affects the guidance of a cladding mode in the second overlay of higher refractive index than the cladding. This causes a more abrupt cladding modal redistribution than with the deposition of a unique high-refractive-index overlay. The phenomenon is analyzed with a method based on a vectorial analysis of modes and the application of coupled mode theory.     

应用于低折射率样品检测的SERS活性液芯光纤

用纳米组装方法在空心光纤内壁修饰SERS活性基底构成内壁具有表面增强拉曼光谱活性层的液芯光纤。激发光由光纤壁横截面入射,并在光纤壁中传播。由于光纤壁的折射率大于检测样品溶液的折射率,使得激发光在光纤壁中发生全反射,并在消逝场下穿透修饰层,激发样品拉曼散射。本方法融合了表面增强拉曼光谱技术与液芯光纤技术的优势,可成为应用于低折射样品溶液体系检测的又一手段。     

A method for the evaluation of the grating envelope in volume holographic media

A novel method for measuring the three-dimensional spatial distribution of gratings in a volume holographic medium is described. In this method, the diffraction of a uniform probe light wave is measured as a function of the deviation (either in angle or wavelength) from the Bragg condition. The envelope function of the grating is obtained by solving the coupled wave equations inversely. Not only the amplitude but also the phase of the envelope function is obtained. This method allows for the depletion of the probe light wave in the hologram and is applicable to both dielectric (refractive index) and absorption gratings. The resolution and the maximum measurable depth in this method are discussed.