多孔阳极氧化铝薄膜光学常数的确定

根据多孔阳极氧化铝(AAO)薄膜的实验透射谱(200—2500nm)，采用极值包络线算法确定其光学常数，并由此较精确地计算出AAO薄膜样品在该波段的光学常数.结果表明，多孔氧化铝薄膜表现出直接带隙(能隙约4．5eV)半导体的光学特性，且其光学常数与制样中的重要工艺参数阳极氧化电压有显著的相关性，即随阳极氧化电压的增加，AAO薄膜的厚度、折射率和光学能隙变大，消光系数减小．同时，计算得到的薄膜厚度与实测值相吻合，则说明计算结果和实验值是自洽的. 关键词： 薄膜光学 光学常数 多孔阳极氧化铝 阳极氧化电压     

Anodized aluminum oxide membranes of tunable porosity with platinum nanoscale-coating for photonic application

We fabricate anodized aluminum oxide (AAO) membranes with platinum (Pt) coating of various thickness ranging from 0 nm to 12 nm. We also demonstrate the tunability of membrane porosity, to add a degree of freedom in addition to the Pt coating, for optical modulation that can be used in photonic application. The reflectance measurement and its analysis are provided based on Fabry–Perot etalon optics that takes into account spectral dependence of optical absorption and loss in the AAO membrane. It is revealed that the frequency-dependent optical finesse (color purity) enhances nonlinearly with the Pt thickness, by the quantitative estimation, while the effective refractive index is substantially governed by the membrane porosity. These features can allow for the AAO membrane to be used as a dye-free color displaying film with efficient tunability of both displaying color and its color purity. In particular, the strong dependence of an effective refractive index on porosity is demonstrated such that the AAO membrane can have the effective refractive index down to about 1.2, making it a possible candidate for a single layer anti-reflection coating material deposited on optical components including low-index glass. We also fabricate, by facile dipping method, an AAO membrane whose pore size changes gradually along a direction on its surface. This intra-membrane modulation of porosity allows it to find application in an optical grating or band-pass filter whose transmission wavelength varies with position on the device surface.     

The effect of mechanical drawing on optical and structural properties of nylon 6 fibres

The Pluta polarizing double-refracting interference microscope was attached to a mechanical drawing device to study the effect of cold drawing on the optical and structural properties of nylon 6 fibres. The microscope was used in its two positions for determining the refractive indices and birefringence of fibres. Different applied stresses and strain rates were obtained using the mechanical-drawing device. The effect of the applied stresses on the optical and physical parameters was investigated. The resulting optical parameters were utilized to investigate the polarizability per unit volume, the optical orientation factor, the orientation angle and the average work per chain. The refractive index and birefringence profiles were measured. Relationships between the average work per chain and optical parameters at different strains rates were determined. An empirical formula was deduced for these fibres. Micro-interferograms are given for illustration.     

Ag/AAO纳米有序阵列复合结构等效光学参量的确定

引入厚度偏差Δd, 修正了薄膜透射率表达式.基于Ag/AAO纳米有序阵列复合结构实验透射光谱(500—2700nm)的两条极值包络线, 定义了一个优化函数, 结合最优化数值算法尝试确定具有较强吸收的Ag/AAO纳米有序阵列复合结构的等效光学参量. 由此计算了该结构的等效折射率n、等效消光系数k、平均等效厚度d以及厚度偏差Δd. 该方法对Ag/AAO纳米复合结构平均等效厚度的相对计算误差仅为0.3%, 与实测厚度基本一致, 且Ag/AAO纳米复合结构的模拟透射谱与实验透射光谱在500—2700nm波段范围内相符. 这表明该计算方法可有效确定Ag/AAO纳米复合结构的等效光学参量, 并与实验结果是自洽的. 关键词： 薄膜光学 光学参量 纳米复合结构 最优化算法     

Automatic fringe analysis of the induced anisotropy of bent optical fibres

A new theoretical model considering the refraction of the incident light beam by the fibre is suggested to determine the refractive index profile of bent optical fibres. This new model (slabs model) considering the cross section of the bent optical fibre consists of large number of slabs. The slabs model bases on the refraction of the incident beam by the fibre. The refractive index profile of the optical fibre cladding before bending obtained using the automated Fizeau interferometer with the aid of suggested model is compared with other models such as, the homogenous model and the multilayer model to verify the ability of this slab model. The refractive index profile of the bent optical fibre cladding is investigated using this suggested model. In addition, the new model is used to obtain the induced birefringence and the guiding parameters. The bending radius is recommended to be greater than 7.1 mm for the used optical fibre. The consideration of the refraction increases the accuracy of the results.     

Controllable nanostructure and optical properties of ZrO2 thin films by glancing angle deposition

In this paper, nanostructured ZrO₂ films were prepared by electron beam evaporation with the glancing angle deposition (GLAD) technique. Columnar films with voids in between formed owing to the self-shadowing effect and the limited diffusion of deposited atoms. The microstructure evolves from slanted columnar structure to helical and pillar structures as the substrate rotational speed increases. The diameter of the columns is in the range of 30–50 nm. A higher rotational speed favors a larger nodule size and a greater surface roughness. Due to the porous structure, the refractive index n of GLAD ZrO₂ films varies from 1.75 to 1.80, lower than that of bulk material. A maximum value of birefringence (Δn=0.03) is obtained in a slanted columnar structure, and the relationship between birefringence and microstructure orientation is discussed. Our results demonstrate that glancing angle deposition is a feasible approach for designing the nanostructure and optical properties of thin films.     

Ellipsometric determination of the optical constants of glassy As2S3 thin films in the weak absorption region

The optical constants (the complex refractive index tensor and the geometrical thickness) of thin freshly prepared unannealed films from glassy chalcogenide As-S semiconductors with the stoichiometric formula As₂S₃ are calculated in the weak absorption region (λ = 0.6328 μm) based on multiangle ellipsometric measurements and taking into account the birefringence of optical waves in such films. The advantage of the approximation of an anisotropic uniaxial film is shown, the values of the ordinary and extraordinary refractive indices are determined, and the difference between them is found to be ∼5 × 10⁻³. Original Russian Text ? M.I. Kozak, V.N. Zhikharev, I.P. Studenyak, I.D. Seĭkovskĭ, 2006, published in Optika i Spektroskopiya, 2006, Vol. 101, No. 4, pp. 602–604.     

Laser biascope for surface stress measurement of tempered glasses

The introduction of gas lasers has greatly increased the number of biascope applications. It has been found that optical waveguide effects caused by the refractive index gradient affected the biascope pattern but, provided that stress birefringence was distinguished, by analyser rotation, from intrinsic refractive index differences between guided modes, and that the birefringence and refractive index values were dissimilar, surface stress determination was possible. Birefringence and refraction patterns were recorded and compared for a variety of glasses.     

A study on optical absorption and constants of doped poly(ethylene oxide)

Thin films of polymer electrolyte based on poly(ethylene oxide) doped with sodium iodide (NaI) were prepared using the solution cast method. The films obtained have average thickness of 70 μm and different NaI concentrations. Absorption and reflectance spectra of UV-radiation were studied in the wavelength range 300-800 nm. The optical results were analyzed in terms of absorption formula for non-crystalline materials.The optical energy gap and the basic optical constants, refractive index, and dielectric constants of the prepared films have been investigated and showed a clear dependence on the NaI concentration. The interpreted absorption mechanism is a direct electron transition.The observed optical energy gap for neat poly(ethylene oxide) is about 2.6 eV, and decreases to a value 2.36 eV for the film of 15 wt% NaI content. It was found that the calculated refractive index and the dielectric constants of the polymer electrolyte thin films increase with NaI content. Models were used to describe the dependences of the dielectric constant on the NaI concentration, and the refractive index on the incident photon energy.     

光学玻璃应力双折射叠加

为解决在光学玻璃应力双折射测量中遇到的双折射叠加问题,利用光学等效原理,使用一个线性双折射模型和一个旋转器来代替叠加模型。对叠加的情况做了分析和计算,得到了叠加后的特征延迟、主应力方向和旋转角随两个应力模型主应力方向夹角变化的曲线。理论分析表明,应力双折射叠加不是应力双折射的简单相加,而是与叠加模型各自的应力双折射值和主应力方向的夹角有关。实验结果与理论计算相吻合。应力双折射叠加对实际光学玻璃测试造成不良影响,使测量精度降低,特别是有透光支撑机构或折射液容器的情况下,应力双折射叠加的影响不可忽略。     

射频磁控反应溅射氮氧化硅薄膜的研究

利用SiOxNy薄膜光学常数随化学计量比连续变化的特性,给出了制备折射率连续可调的SiOxNy薄膜的实验条件。用磁控反应溅射法制备了不同氮氧比的SiOxNy薄膜。研究了不同气流比率条件下薄膜光学常数、化学成分及溅射速率等的变化。用UV-VIS光谱仪测试了透射率曲线,利用改进的单纯型法拟合透射率曲线计算得到了折射率和消光系数。测试了红外傅立叶光谱(FTIR)曲线和X光光电子能谱(XPS)分析了薄膜成分的变化。实验表明薄膜特性与N2／O2流量比率密切相关,通过控制总压和改变气体流量比可控制SiOxNy薄膜的折射率n从1．92到1．46连续变化,应用Wemple-DiDomenico模型计算出光子带隙在6．5eV到5eV之间单调变化。     

退火温度对GdBO3∶Eu3+/AAO薄膜形貌和发光性质的影响

利用水热反应和高温退火,在100 nm孔径的多孔氧化铝(AAO)模板表面制备了GdBO3∶Eu3+/AAO发光薄膜。通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)和光致发光(PL)等手段表征了GdBO3∶Eu3+/AAO薄膜的结构、形貌和发光性质。SEM显示GdBO3∶Eu3+/AAO的形貌可通过调节退火温度控制。XRD和PL的结果表明,在AAO模板的表面所组装的GdBO3∶Eu3+为六方碳钙石型(Vaterite-type)结构。PL的结果表明:5D0→7F2和5D0→7F1的相对发射强度与退火温度有关,5D0→7F2红色发射与5D0→7F1橙色发射之比值随退火温度的降低而增加,降低退火温度可使GdBO3∶Eu3+/AAO样品的色纯度得到改善。     

Analysis of codeposited Gd2O3/SiO2 composite thin films by phase modulated spectroscopic ellipsometric technique

Tailoring of the refractive index of optical thin films has been a very fascinating as well as challenging topic for developing new generation optical coatings. In the present work a novel Gd₂O₃/SiO₂ composite system has been experimented and probed for its superior optical properties through phase modulated spectroscopic ellipsometry, spectrophotometry and atomic force microscopy. The optical parameters of the composite films have been evaluated using Tauc-Lorentz (TL) formulations. In order to derive the growth dependent refractive index profiles, each sample film has been modeled as an appropriate multilayer structure where each sub-layer was treated with the above TL parameterizations. All codeposited films demonstrated superiority with respect to the band gap and morphological measurements. At lower silica mixing compositions such as in 10-20% level, the composite films depicted superior spectral refractive index profile, band gap as well as the morphology. This aspect highlighted the fact that microstructural densifications in composite films can override the chemical compositions while deciding the refractive index and optical properties in such thin films.     

Optical properties of amorphous HF–In–Zn–O thin films estimated from transmission spectra

Amorphous and flat (<1 nm roughness) Hf–In–Zn–O thin films were prepared by radio frequency (rf) magnetron sputtering method at room temperature (RT) and at 300 °C substrate temperature. The crystal structure and surface morphology were investigated by high resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM), respectively. Optical properties of these films were obtained from the UV–VIS–NIR transmission spectra, at normal incidence, over the 200–2000 nm spectral range. Swanepoel's method was used to calculate the thickness and the refractive index of the films. The dispersion of refractive index was obtained in terms of the single-oscillator Wemple–DiDomenico model. The optical absorption edge was described using the direct transition model proposed by Tauc. The film deposited at higher substrate temperature had lower optical band gap, higher refractive index, higher oscillator strength and energy of the effective dispersion oscillator. Optical characterization shows that films become more stable, relaxed and rigid at higher substrate temperature.     

Stress effects in prism coupling measurements of thin polymer films

Due to the increasingly important role of some polymers in optical waveguide technologies, precise measurement of their optical properties has become important. Typically, prism coupling to slab waveguides made of materials of interest is used to measure the relevant optical parameters. However, such measurements are often complicated by the softness of the polymer films when stress is applied to the prism to couple light into the waveguides. In this work, we have investigated the optical properties of three different polymers, polystyrene (PS), polymethyl-methacrylate (PMMA), and benzocyclobutane (BCB). For the first time, the dependence of the refractive index, film thickness, and birefringence on applied stress in these thin polymer films was determined by means of the prism coupling technique. Both symmetric trapezoid shaped and right-angle prisms were used to couple the light into the waveguides. It was found that trapezoid shaped prism coupling gives better results in these thin polymer films. The refractive index of PMMA was found to be in the range of 1.4869 up to 1.4876 for both TE and TM polarizations under the applied force, which causes a small decrease in the film thickness of up to 0.06 m. PMMA waveguide films were found not to be birefringent. In contrast, both BCB and PS films exhibit birefringence albeit of opposing signs. PACS 42.82.Et; 78.20.Ci; 78.20.Fm     

Optical Elements with Subwavelength Structured Surfaces

Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive element regime, and fabrication methods of the elements are explained.     

Optical properties of a liquid crystal with small ordinary and extraordinary refractive indices and small optical anisotropy

Optical properties of a nematic liquid crystal with small refractive index and small birefringence were studied. The ordinary and extraordinary refractive indices and birefringence were measured as functions of temperature by using an Abbe refractometer and wedge nematic cells. From values of these indices the nematic orientational order parameter was calculated by using several methods and corresponding mathematical models. Kuczyński et al. method was found to be suitable for determining the order parameter also for materials featuring small ordinary refractive index, with unknown density.     

Effects of high-energy ion-beam irradiation on structural and optical properties of (Mg0.95Co0.05)TiO3 thin films

We report the structural and optical properties of high-energy ion-beam irradiated Co-doped magnesium titanate thin films. (Mg_0.95Co_0.05)TiO₃ (MCT) thin films were deposited on quartz substrates using radio frequency magnetron sputtering. Subsequently, the films were annealed for crystallinity and were irradiated with 100?MeV Ag ions by varying the ion fluence. The X-ray diffraction patterns of the films before and after the irradiation were refined using the Rietveld refinement and the variations in the lattice parameters were correlated with the ion fluence. Although, annealing of thin films results in an enhancement in refractive index and optical bandgap, the ion fluence induces significant changes in the refractive index and optical bandgap. Atomic force microscopy is employed to study the surface morphology of the films. The impact of ion fluence on structural and optical properties of MCT thin films has been investigated.     

长周期光纤光栅气敏薄膜传感器结构优化

基于三包层长周期光纤光栅模型,研究了包层表面涂覆一层溶胶凝胶气敏薄膜的长周期光纤光栅化学传感器的灵敏度Sn与薄膜光学参量(折射率n3和厚度h3)和光纤光栅结构参量(光栅周期、折变量和光栅长度)之间的关系。采用最优化数值方法,找到了获得高灵敏度所需的最佳膜层光学参量和光栅结构参量。理论计算表明,该类型传感器对膜层折射率的测量分辨率高达10-8。实验上制作了对乙醇气体敏感的传感器,并证实了传感器结构优化的必要性。     

聚甲基丙烯酸甲酯和聚碳酸酯各向异性光学性质理论研究

作为重要的光学薄膜材料,聚甲基丙烯酸甲酯(PMMA)和聚碳酸酯(PC)在诸多工业领域已得到广泛应用.本文利用密度泛函理论结合分子动力学方法深入系统地研究了这两种聚合物的各向异性光学性质,并对比分析了不同分子链长度和微观结构对其各向异性光学性质的影响.计算结果表明PMMA和PC都具有较高的本征双折射率,且分子链长度对本征折射率的影响显著.在可见光范围内,单体单元PMMA本征双折射率在10%以上,而三单元结构本征折射率则不到4%.对于体相结构多聚体,从立方结构拉伸到厚度仅有6?的过程中,PC不同方向折射率最大差异高达6%,而同样情况下PMMA不同方向折射率差异仅有1.3%.此项研究有助于理解PMMA和PC聚合物各向异性光学特征产生的原因和影响因素,从而进一步指导和促进其在更多领域的发展与应用.