一种硅基金属狭缝表面等离子体波导的设计

设计了一种适用于光电子集成电路的表面等离子体波导结构.利用三维全矢量时域有限差分法对该波导结构进行了数值模拟,并分析了其在基模传输时的模式场分布与金属结构顶角的关系以及其能量限制性.研究了该波导结构在不同金属材料下的有效折射率和传播长度对芯层宽度的依赖关系,讨论了两个该波导结构之间的耦合长度、最大转移功率和彼此间的串扰.结果表明:光场被高度限制在芯层区域,在金属结构顶角为135°时,其能量限制因子更高;在金属材料确定的情况下,有效折射率随芯层宽度增大而减小,而传播长度增大;在芯层宽度一定的条件下,两个波导结构间的耦合长度随波导间距增大而增大,最大转移功率和串扰随波导间距增大而减小.     

Theoretical Analysis of Silicon-Based Integrated-Optic Mach-Zehnder Pressure Sensors

Silicon-based Mach–Zehnder integrated-optic pressure sensors are investigated in this article. Several structures proposed in the literature are examined and performance parameters such as power leakage towards the Si substrate, radiation loss as a function of the Y-junction aperture angle, and halfwave pressure are analyzed. Modeling of the material deformation characteristics and refractive index change as a function of the applied pressure is carried out by using the finite-difference technique. The sensor optical characteristics and waveguiding properties are computed by using the finite-difference beam-propagation method (FD-BPM) and the extended effective index method (EEIM). Guidelines for performance optimization are proposed.     

In‐band pumped Ti:Tm:LiNbO3 waveguide amplifier and low threshold laser

The fabrication by diffusion doping and a detailed optical investigation of a Ti:Tm:LiNbO₃ waveguide amplifier and of a Fabry‐Pérot type Ti:Tm:LiNbO₃ laser are reported. Both devices are in‐band pumped by a laser diode at 1650 nm. The wave‐guide amplifier shows broad‐band optical gain in the wavelength range 1750 nm < λ < 1900 nm. The laser emits at 1890 nm, the longest emission wavelength of a Tm:LiNbO₃ laser reported so far; also 1850 nm emission could be demonstrated. Laser threshold (1890 nm) is at 4 mW coupled pump power; the slope efficiency is ∼13.3%. Properties and potential of both devices are analyzed by extensive modeling.     

Oxygen bridged nitroanilines for quadratic nonlinear optics

Several nitro aromatic compounds bridged by an oxygen atom have been synthesized and their linear and nonlinear optical properties have been investigated. In one of the compounds (1), a powder SHG efficiency of 6.2 times of urea was observed while its absorption lies in the UV region. The highest molecular hyperpolarizability β, measured was 230×10⁻³⁰ for a compound (8f) with increased conjugation. Thermal stability of these compounds has been checked using differential scanning calorimetry and the decomposition temperature (T_d) was found to be high and lying between 266-298 °C. These molecules have potential importance as thermally stable, visible-transparent second order NLO materials.     

The Reactivity Ratios of Acrylonitrile Copolymerization

The reactivity ratios of acrylonitrile copolymerization published from 1971to 1982 are tabulated.     

Diffuse reflections and the symmetry of vesuvianite

Vesuvianite is a common rock-forming silicate mineral with the general chemical formula X₁₉Y₁₃Z₁₈T_0.5O₆₈W₁₀ , where X = Ca, Na, Ln, Pb, Sb; Y= Al, Mg, Fe, Ti, Mn, Cu, Zn; Z = Si; T= B; W= (O, OH, F). Vesuvianite is ideally tetragonal with space group P4/nnc, but many samples show physical properties that indicate deviations from this symmetry. Many vesuvianite samples are optically biaxial; a sector-zoned crystal from Quebec shows {100}, {010} and {001} sectors with low (0° to 5°), intermediate (approximately 36°) and high (approximately 60°) 2V values, respectively. X-ray precession photographs of fragments from each of the sectors show that the number and intensity of glide-violating reflections increase in the sequence {101} →{001} →{100}; in addition, deviations from 4/mmm Laue symmetry were also apparent. Diffuse streaking is associated with the violating reflections. A combination of the optical and X-ray evidence indicates that vesuvianite is monoclinic. However, attempts to refine the crystal structure in monoclinic space groups have been inconclusive.     

Suppression of first order stimulated Raman scattering in erbium-doped fiber laser based LIDAR transmitters through induced bending loss

A model is presented for suppression of first-order stimulated Raman scattering (SRS) in pulsed Er-doped fiber amplifiers with wavelength-selective induced bending loss. The model estimates the effectiveness of SRS suppression through fiber coiling in a pulsed amplifier, considering both the single- and dual-clad fiber cases. The basic approach is to fit analytical expressions to the evolution of a quasi-CW signal in the amplifier. Then, assuming that SRS does not deplete the signal, exact analytical expressions for the propagation of the Stokes wave are determined, from which the SRS threshold is estimated. Finally, example calculations are presented, and the model is used to determine a fiber geometry for the suppression of SRS through fiber coiling.     

Giant Mid-Infrared Second-Harmonic Generation Response in a Densely-Stacked Van Der Waals Transition-Metal Oxychloride

Second-harmonic generation (SHG) is a fundamental optical property of nonlinear optical (NLO) crystals. Thus far, it has proved difficult to engineer large SHG responses, particularly in the mid-infrared region, owing to the difficulty in simultaneously controlling the arrangement and density of functional NLO-active units. Herein, a new assembly strategy employing functional modules only, and aimed at maximizing the density and optimizing the spatial arrangement of highly efficient functional modules, has been applied to the preparation of NLO crystals, affording the van der Waals crystal MoO₂Cl₂. This exhibits the strongest powder SHG response (2.1×KTiOPO₄ (KTP) @ 2100 nm) for a transition-metal oxyhalide, a wide optical transparency window, and a sufficient birefringence. MoO₂Cl₂ is the first SHG-active transition-metal oxyhalide effective in the infrared region. Theoretical studies and crystal structure analysis suggest that the densely packed, optimally-aligned [MoO₄Cl₂] modules within the two-dimensional van der Waals layers are responsible for the giant SHG response.     

Fermat et le principe du moindre temps

The principle of least time was first conceived by mathematicians-physicists, such as Ibn al-Haytham (Alhazen), as the principle of the easiest way followed by the light ray. It was not until the invention of the maximum and minimum method by Pierre de Fermat that this principle, stated in the Book of Optics of Ibn al-Haytham, became the principle of least time. This article examines the history of this principle in ancient and classical optics.     

BEPC-Ⅱ同步光光学诊断系统研究

提出了用同步光进行BEPC-Ⅱ束流测量.分析了用同步光进行BEPC-Ⅱ光学诊断的可行性,并详细讨论了BEPC-Ⅱ同步光光学诊断系统实现方案.