Optimization of the structure of an optical fiber polarizer with a metal film at a wavelength of 980 nm

The dependence of the extinction ratio of a 980-nm fiber polarizer with an Al film on the thickness of magnesium fluoride buffer layer has been experimentally and theoretically investigated. At the optimal thickness of the buffer layer, h _b = 0.078 (normalized to the wavelength), extinction ratios of 23 and 41 dB were obtained for polarizers having fiber shell residual layers of 2.01 and 1.607 μm, respectively. The optimal thin-film structure is determined, which will make it possible to design polarizers with extinction ratios up to 100 dB.     

高量级光衰减时对线偏振片组衰光系数的研究

利用琼斯矢量法推导实际偏振片的琼斯矩阵和两片偏振片组的透射光强表达式和衰光系数表达式.通过计算说明,在高量级光衰减时用马吕斯定律计算偏振片的衰光率存在一定误差.因此,该衰光系数表达式可作为马吕斯定律实际运用时的修正式.依据该理论推导得出两偏振片组的最大衰光率为2ε2,并得到三偏振片组的关于θ2的透射光强表达式.该式以及相应实验表明在θ1,θ2=90°,135°和90°,315°时最大衰光率可达到2ε4.     

Quasi-Resonant Enhancement of the Extinction Ratio in the Amorphous Silicon Nanowire Grid Polarizer

Spectral characteristics of thin-film nanowire grid polarizers based on amorphous silicon are numerically investigated. The extinction ratio, transmission coefficients, and reflection coefficients are calculated using the MC Grating code based on the rigorous coupled-wave analysis. It is found out that at particular structure parameters of the nanowire grid polarizer the extinction ratio increases to 10⁶ at the optical radiation wavelength of about 380 nm, which is characterized as a quasi-resonance effect. A dissipative-interference qualitative interpretation of this effect within the waveguide model is proposed. This interpretation is confirmed by the calculated field distribution patterns in the vicinity of the quasiresonance.     

Fabrication of a mid-IR wire-grid polarizer by direct imprinting on chalcogenide glass

A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.5-11 μm wavelengths. This polarizer with a high extinction ratio can be fabricated more simply and less expensively than conventional IR polarizers.     

High extinction ratio metal-insulator-semiconductor waveguide surface plasmon polariton polarizer

The attenuation characteristics of a multilayer metal clad GaAs-AlGaAs optical waveguide polarizer are theoretically investigated. The dispersion relations and field distribution of the multilayer structures are calculated for different geometrical parameters and material properties. The polarizer studied consists of a single mode finite/infinite metal clad GaAs-AlGaAs waveguide with a dielectric (SiO₂/Si₃N₄) buffer layer inserted between the metal and the waveguide.Conventionally, the TM polarized waves are found to exhibit an absorption peak at a particular buffer thickness (called critical buffer thickness).We shall show that the maximum TM absorption can be improved by a multiple factor up to 7 by choosing a buffer layer thicker than its critical value. This corresponds to an extinction ratio of 1470 dB for a polarizer length of 1 mm. Further, thicker buffers reduce the insertion losses and values as low as 0.1 dB can be obtained. The strong TM absorption in these structures is interpreted as resonant coupling of the guided mode to the lossy surface plasmon polariton supported by the thin metal film. Thicker buffer also reduces the TE losses (insertion losses) and hence increases the extinction ratio (ratio of TM to TE losses).This can be achieved by optimizing the buffer and the metal thicknesses. Another equally efficient polarizer can be designed by positioning a dielectric (same as buffer) layer (superstrate layer) above the metal film and then optimizing the buffer, metal and the superstrate thicknesses. We also show that the proposed polarizer with the superstrate layer is highly stable even when exposed to the extreme atmospheric changes.     

Design of Metal-clad Ti: LiNbO_3 Polarizer

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Subwavelength gratings fabricated on semiconductor substrates via E-beam lithography and lift-off method

We present results of the fabrication and measurements on reflective polarizers consisting of stacked bi-layer subwavelength metal gratings prepared on GaAs (100) substrates. These linear gratings were fabricated using electron-beam direct-writing lithography and the lift-off method with periods less than the wavelength of light used for measurements. At normal incidence, the polarizer reflects the light polarized perpendicular to the grating lines (transverse magnetic polarization, TM polarized) but absorbs parallel-polarized light (transverse electric polarization, TE polarized). By optimizing structural parameters, the polarization extinction ratio close to 20 has been experimentally achieved at wavelength of 650 nm.     

Strange axial-vector mesons mixing angle

The masses of K ₁(³ P ₁) and K ₁(¹ P ₁) are considered in a nonrelativistic constituent quark model, and the absolute value of the K ₁(³ P ₁)- K ₁(¹ P ₁) mixing angle is determined to be about 59.29^°. The comparison of the theoretical predictions on the strong decay widths of K ₁(1270) and K ₁(1400) in the ³ P ₀ decay model as well as the production ratio of these two states in the τ decay between the available experimental data strongly favors that the K ₁(³ P ₁)- K ₁(¹ P ₁) mixing angle is about +59.29^°.     

Testing of linear polarizer using photorefractive effect

A new method is developed to test linear polarizers using two-wave mixing in photorefractive Bi₁₂TiO₂₀ (Bismuth Titanium Oxide, BTO). The extinction ratios obtained from this method was comparable with the literature values and the method is also useful for qualitative analysis of linear polarizers. Detailed theoretical and experimental analysis is given in the paper.     

基于多层膜偏振元件的软X射线磁光Faraday偏转测量

在北京同步辐射装置(BSRF)的3W1B软X射线光束线上利用自行研制的同步辐射软X射线综合偏振测量装置对Ni的M_2,3边附近(60—70 eV)进行了软X射线磁光(magneto-optical)法拉第效应(Faraday effect)的偏转测量,实验装置主要由起偏器,检偏器,样品架,圆形钕铁硼永磁铁和MCP探测器组成,偏振元件(起偏元件和检偏元件)均采用反射式非周期性Mo/Si宽带多层膜.实验采用反射起偏和反射检偏的模式,得到一系列能量范围在60—70 eV间的法拉第偏转角结果, 关键词： 软X射线 磁光Faraday效应 综合偏振测量装置 宽带多层膜     

Co1-xNixSb3-ySey热电输运中晶界和点缺陷的耦合散射效应

结合机械合金化与放电等离子烧结工艺制备了Ni和Se共掺的细晶方钴矿化合物Co_1-xNi_xSb_3-ySe_y,研究了晶界和点缺陷的耦合散射效应对CoSb₃热电输运特性的影响.通过Ni掺杂优化载流子浓度提高功率因子.在x=0.1时,功率因子达到最大值1750μWm^-1K^-2(450℃),是没有掺Ni试样的两倍.晶界和点缺陷的耦合散射机理使晶格热导率急剧下降,其中Co_0.9Ni_0.1Sb_2.85Se_0.15的室温晶格热导率降低至1.67Wm^-1K^-1,接近目前单填充效应所能达到的最低值1.6Wm^-1K^-1,其热电优值ZT在450℃时达到最大值0.53.将Callaway-Von Baeyer点缺陷散射模型嵌入到Nan-Birringer有效介质理论模型,对晶界散射和点缺陷散射的耦合效应对热导率的影响进行了定量分析,模型计算与实验结果符合.理论模型计算表明,当晶粒尺寸下降到50nm同时掺杂引入点缺陷散射后,Co_0.9Ni_0.1Sb_2.85Se_0.15的晶格热导率下降到0.8Wm^-1K^-1. 关键词： 3')" href="#">CoSb₃ Ni和Se掺杂 热电性能 耦合散射效应     

Effects of the polarizer parameters upon the performance of an optical current sensor

Extinction ratio is an important parameter of a polarizer, and the bias angle of the polarizer used in optical current sensing systems is also an important adjustable parameter. Both of them can certainly affect the performance of the sensing systems. In this paper, the effects of the extinction ratio and bias angle error of polarizers upon the output characteristics of an optical current sensor are investigated theoretically and experimentally; some useful results are given for the optical current sensor researchers and designers.     

ConC3-/0和ConC4-/0(n=1~4)团簇的结构和电子特性:尺寸选择的负离子光电子能谱和密度泛函理论研究

We investigated the structural evolution and electronic properties of Co_nC₃^-/0 and Co_nC₄^-/0 (n=1-4) clusters by using mass-selected photoelectron spectroscopy and density functional theory calculations. The adiabatic and vertical detachment energies of Co_1-4C₃^- and Co_1-4C₄^- were obtained from their photoelectron spectra. By comparing the theoretical results with the experimental data, the global minimum structures were determined. The results indicate that the carbon atoms of Co_nC₃^-/0 and Co_nC₄^-/0 (n=1-4) are separated from each other gradually with increasing number of cobalt atoms but a C₂ unit still remains at n=4. It is interesting that the Co₂C₃^- and Co₂C₄^- anions have planar structures whereas the neutral Co₂C₃ and Co₂C₄ have linear structures with the Co atoms at two ends. The Co₃C₃^- anion has a planar structure with a Co₂C₂ four-membered ring and a Co₃C four-membered ring sharing a Co-Co bond, while the neutral Co₃C₃ is a three-dimensional structure with a C₂ unit and a C atom connecting to two faces of the Co₃ triangle.     

Observation of forbidden transitions in the ν4 band of NH3: corrections to the ground state ΔK = 3 intervals

This paper presents a preliminary evaluation of the C rotational constant and coefficients of the operators P_z ²ⁿ up to n = 4 for NH₃ in the ground state. These constants are evaluated on the basis of the determination of 14 different ΔK = 3 ground state intervals obtained from measurement of many Δ(K - l) = 3 transitions observed in the ν₄ vibration rotation band. Corrections to the ground state term values for NH₃ are given as a function of K, thus permitting ΔK = 3 transitions to be determined with accuracies comparable to those of normal allowed transitions. The perturbation which gives rise to the observed transitions is large, but has not been treated in previous analyses of the ν₄-2ν₂ bands.     

White light interferometry test and analysis of LiNbO3 polarizer

White light interferometer can be used to measure the amplitude extinction ratio (ER) of polarizer and coupling distribution in fiber. A LiNbO₃ polarizer coupled with a polarization maintaining fiber and a silica planar waveguide at the two ends was measured using white light interferometer. According to the principles of optical coherence domain polarimeter (OCDP) technique, the test scheme is analyzed and presented to measure the ER of LiNbO₃ polarizer with its apparatus proposed correspondingly. By analyzing the interference intensity, both the ER of LiNbO₃ polarizer and its coupling crosstalk with optical fiber and waveguide are obtained. The results illustrate that the ER of a 5 mm-long LiNbO₃ polarizer is 71 dB and the crosstalk of the coupling points are around 40 dB. The results have good agreement with analysis.     

High-Resolution Infrared and Millimeter-Wave Study of the v(3) = 1 State of HSiF(3) and DSiF(3)

Millimeter-wave spectra of HSiF₃ and DSiF₃ in the v₃ = 1 excited state have been measured from 100 to 490 GHz. Infrared spectra have been recorded in the ν₃ regions, ν₀ 424.0301 and 420.9320 cm⁻¹ in HSiF₃ and DSiF₃, respectively, with a resolution of 2.4 × 10⁻³ cm⁻¹. Since in both species the parameters α^B₃ and α^C₃ have very similar values, no K structure could be resolved in the ^QP and ^QR clusters for low-to-medium K values. For high J the effect of the ground state D_JK term more and more dominates and spreads the J clusters into opposite directions such that medium-to-high K components, particularly those with K = 3p, are resolved. Rotational and infrared data have been fitted together using a model up to sextic centrifugal distortion constants. No perturbations were indicated. Hot bands (ν₃ + nν₆)–nν₆ with n = 1, 2, and 3 have been detected and analyzed.     

Improvement of polarization extinction in silicon waveguide devices

The SOI based waveguide devices are found to be highly polarization sensitive. Unwanted polarization excitations can be attenuated by integrating a TE- or TM-pass polarizer. A large attenuation of TM-polarized light has been observed when a thin film of metal is coated on the top of silicon rib waveguide, while TE-polarized light remains almost unaffected. The attenuation of TM-polarized light is attributed to the plasmonic absorption of the evanescent field in the metal cladding. Typically, with an Al cladding of thickness ～ 100 nm and a length of 1 mm on top of a single-mode (λ ～ 1550 nm) SOI rib waveguide structure, TE vs TM extinction ratio of ～ 15 dB has been obtained. Integrating such waveguide polarizers in a directional coupler and MZI based DWDM channel interleaver, we have also achieved an improvement in polarization extinction by ～ 15 dB.     

Temperature‐dependent Raman spectroscopic studies of microstructure present in dipotassium molybdate crystals and their melts

Temperature‐dependent Raman spectra of K₂Mo_nO_3n+1 (n = 1, 2, 3) crystals up to and above their melting points were recorded, and their vibration modes in solid and molten states were assigned. Basic structural units and the corresponding cluster forms in molten dipotassium monomolybdates, dimolybdates, and trimolybdates were studied by in situ high‐temperature Raman spectroscopic studies together with theoretical calculations, including density functional theory and quantum chemistry ab initio calculation. Anion units of [MoO₄]²⁻, [Mo₂O₇]²⁻, and [Mo₃O₁₀]²⁻ were shown to principally exist in molten K₂MoO₄, K₂Mo₂O₇, and K₂Mo₃O₁₀, respectively. The mechanisms of the microstructural evolution of K₂Mo_nO_3n+1 (n = 1, 2, 3) crystals while being melted are schematically illustrated. Copyright © 2016 John Wiley & Sons, Ltd.     

Time-dependent self-consistent perturbation theory and applications to molecules

The two most intense bands of the 370 nm electronic band system of tropolone have been rotationally analysed. They are separated by 18·93 cm^-1 and it has been shown that the high wavenumber band is the 0^--0^- (H₁ ¹) transition in what is almost certainly the internal hydrogen-bonding vibration v _H : the low wavenumber band is the 0⁺-0⁺ (0₀ ⁰) transition. A rotational contour analysis of both bands shows that there is an intensity alternation in K _a″ such that the ratio K _a″ even : odd is 10 : 6 in the 0⁺-0⁺ band and 6 : 10 in the 0^--0^- band. The intensity alternation, the nearly equal intensities of the 0⁺-0⁺ and 0^--0^- bands, the separation of these two bands and the anharmonic behaviour of v _H show that the separation of the 0⁺ and 0^- levels is small in the ground electronic state (probably less than 50 cm^-1) and is 18·93 cm^-1 larger in the excited electronic state.

The 0⁺-0⁺ and 0^--0^- bands are both type B showing that the electronic transition is à ¹ B ₂-X ¹ A ₁ and therefore π*-π rather than π*-n. The π*-n transition is probably shifted to high wavenumber by the internal hydrogen-bonding.     

Lidar measurements of atmospheric aerosol as a function of relative humidity

Hänel and Frankenberger have related the extinction coefficient and standard visibility to the relative humidity. It has been assumed that these relations also apply to the backscatter coefficient. Lidar measurements of atmospheric backscatter have confirmed that the assumption is reasonable and provide a means of distinguishing between air masses with different aerosol contents.Notation _k extinction coefficient of sample - V _k volume of sample - N _k number of particles in sample - r _j equivalent radius of particle - K _j extinction efficiency factor for particle - r _k characteristic radius of particle in sample - K _k characteristic extinction efficiency factor - S _k total extinction efficiency factor - f relative humidity - solid angle - _k() scattering coefficient at angle - _j ^* scattering phase shift parameter of particle - m _j complex refractive index of particle - wavelength - Q ratio of particle cross-section areas [4] - exponent in Kasten's relation - R ratio of backscatter coefficients