Parametric oscillation in vertical triple microcavities

Optical parametric oscillation is a nonlinear process that enables coherent generation of 'signal' and 'idler' waves, shifted in frequency from the pump wave. Efficient parametric conversion is the paradigm for the generation of twin or entangled photons for quantum optics applications such as quantum cryptography, or for the generation of new frequencies in spectral domains not accessible by existing devices. Rapid development in the field of quantum information requires monolithic, alignment-free sources that enable efficient coupling into optical fibres and possibly electrical injection. During the past decade, much effort has been devoted to the development of integrated devices for quantum information and to the realization of all-semiconductor parametric oscillators. Nevertheless, at present optical parametric oscillators typically rely on nonlinear crystals placed into complex external cavities, and pumped by powerful external lasers. Long interaction lengths are typically required and the phase mismatch between the parametric waves propagating at different velocities results in poor parametric conversion efficiencies. Here we report the demonstration of parametric oscillation in a monolithic semiconductor triple microcavity with signal, pump and idler waves propagating along the vertical direction of the nanostructure. Alternatively, signal and idler beams can also be collected at finite angles, allowing the generation of entangled photon pairs. The pump threshold intensity is low enough to envisage the realization of an all-semiconductor electrically pumped micro-parametric oscillator.     

铁磁和反铁磁晶体中非线性电磁波的传播特性

本文对在铁磁和反铁磁晶体中传播的电磁波的下列非线性贡象作了简要论述：（１）非线性磁化效应引起的静磁波的频率转换，（２）周期皱纹波导中非线性静磁表面波的禁带频移，（３）静磁波激发的光波模耦合，（４）电磁波经反铁磁膜层透射的功率多稳效应．     

超导材料的超快光谱研究

电子、晶格、自旋和轨道微观自由度对超导材料的宏观特性起到至关重要的作用.在超导体系中,特别是非常规超导材料,这些自由度衍生出具有不同能量尺度的玻色激发和有序态.前者如声子、磁振子、电荷密度波、自旋密度波、自旋涨落、向列涨落等;后者如超导态、赝能隙态、向列相、反铁磁/铁磁等.前者与后者的形成密切相关.尤其是,不同的玻色激发在频域内纠缠在一起彼此相互作用,同时又与电子(或准粒子)耦合,构建出复杂而又丰富的平衡态和非平衡态物理过程.超快光谱技术的独特性在于具有宽能量范围和高时间分辨率的特点,利用光(电磁波)与超导材料相互作用中的线性和非线性响应,可以共振或非共振地探测与调控这类材料中的准平衡或非平衡态动力学属性.因为桌面超快光谱系统功能全面且具有很大的灵活性,它不仅被应用于超导体系,而且被广泛应用于其他各种无机和有机材料.由于非平衡态理论,特别是与关联电子体系相关的,目前还处在快速发展的阶段,所以本综述主要介绍了常用的桌面超快光谱技术和目前被广泛使用的相关分析理论,聚焦于讨论超导材料中超快光谱实验数据涌现出来的一些普适性趋势及进展.所涉及的超导材料包含了常规超导体、铜氧化物超导体、铁基超导体和重费米子超导体.     

3~5 μm AgGaS2光参量振荡器的优化分析

研究调Q Nd∶YAG(1.064 μm)激光器泵浦的AgGaS₂光学参量振荡器. 根据三波互作用的相位匹配原理, 分析AgGaS₂光学参量振荡器的Ⅰ类相位匹配角、 角度调谐曲线和有效非线性系数等动力学参数. 计算在小信号近似下, 允许角随输出波长和晶体长度的变化规律, 并讨论允许角对相位失配系数的影响. 在允许的相位失配范围内, 研究晶体长度对转换效率的影响.      

双轴晶体有效非线性系数精确表达式

考虑了晶体内基频光电位移矢量D.电场强度矢量E的离散及倍频光极化矢量P,电位移矢量D的离散,推出了双轴晶体有效非线性系数(d_(eff))的精确表达式,讨论了有效非线性系数绝对值的对称性并给出了双轴晶体TSCCC和dLAP的有效非线性系数的空间分布。     

空间光孤子之间相互作用的数值研究

从麦克斯韦方程组出发,考虑光波介质的各向同性,在慢变包络近似下,得到了一般情况下的（1＋1）维非线性薛定讶方程;研究了一维自聚焦介质中线性聚焦和散焦效应对空间孤子之间相互作用的影响;并讨论了不同条件下空间光孤子之间的相互作用．     

Colloidal ordering from phase separation in a liquid-crystalline continuous phase

Some binary mixtures exist as a single phase at high temperatures and as two phases at lower temperatures; rapid cooling therefore induces phase separation that proceeds through the initial formation of small particles and subsequent growth and coarsening. In solid and liquid media, this process leads to growing particles with a range of sizes, which eventually separate to form a macroscopically distinct phase. Such behaviour is of particular interest in systems composed of an isotropic fluid and a liquid crystal, where the random distribution of liquid-crystal droplets in an isotropic polymer matrix may give rise to interesting electro-optical properties. Here we report that a binary mixture consisting of an isotropic fluid and a liquid crystal forming the continuous phase does not fully separate into two phases, but self-organizes into highly ordered arrays of monodisperse colloidal droplet chains. We find that the size and spatial organization of the droplets are controlled by the orientational elasticity of the liquid-crystal phase and the defects caused by droplets exceeding a critical size. We expect that our approach to forming monodisperse, spatially ordered droplets in liquid crystals will allow the controlled design of ordered composites that may have useful rheological and optical properties.     

Liquid crystal 'blue phases' with a wide temperature range

Liquid crystal 'blue phases' are highly fluid self-assembled three-dimensional cubic defect structures that exist over narrow temperature ranges in highly chiral liquid crystals. The characteristic period of these defects is of the order of the wavelength of visible light, and they give rise to vivid specular reflections that are controllable with external fields. Blue phases may be considered as examples of tuneable photonic crystals with many potential applications. The disadvantage of these materials, as predicted theoretically and proved experimentally, is that they have limited thermal stability: they exist over a small temperature range (0.5-2 degrees C) between isotropic and chiral nematic (N*) thermotropic phases, which limits their practical applicability. Here we report a generic family of liquid crystals that demonstrate an unusually broad body-centred cubic phase (BP I*) from 60 degrees C down to 16 degrees C. We prove this with optical texture analysis, selective reflection spectroscopy, K?ssel diagrams and differential scanning calorimetry, and show, using a simple polarizer-free electro-optic cell, that the reflected colour is switched reversibly in applied electric fields over a wide colour range in typically 10 ms. We propose that the unusual behaviour of these blue phase materials is due to their dimeric molecular structure and their very high flexoelectric coefficients. This in turn sets out new theoretical challenges and potentially opens up new photonic applications.     

光纤中的调制不稳定性分析

利用时间相关的变分法对光纤光学系统中平面波调制的不稳定性进行研究,在拉格朗日变分的框架下推导出相位与振幅的演化方程,进而对线性化扰动方程的解进行了数值模拟,得出调制不稳定性下扰动功率随传输距离的变化关系     

Optical isotropy and iridescence in a smectic 'blue phase'

When liquid crystal molecules are chiral, the twisted structure competes with spatially uniform liquid crystalline orders, resulting in a variety of modulated liquid crystal phases, such as the cholesteric blue phase, twist grain boundary and smectic blue phases. Here we report a liquid crystal smectic blue phase (SmBP(iso)), formed from a two-component mixture containing a chiral monomer and a 'twin' containing two repeat units of the first molecule connected by a linear hydrocarbon spacer. The phase exhibits the simultaneous presence of finite local-order parameters of helices and smectic layers, without any discontinuity on a mesoscopic length scale. The anomalous softening of elasticity due to a strong reduction in entropy caused by mixing the monomer and the twin permits the seamless coexistence of these two competing liquid crystal orders. The new phase spontaneously exhibits an optically isotropic but uniformly iridescent colour and automatically acquires spherical symmetry, so that the associated photonic band gap maintains the same symmetry despite the local liquid crystalline order. We expect a range of unusual optical transmission properties based on this three-dimensional isotropic structure, and complete tunability due to the intrinsic softness and responsiveness of the liquid crystalline order against external fields.     

智能材料及其应用

智能材料是一种能感知外界环境变化并自动改变自身特性以适应该变化的新型复合材料，具有广阔的应用前景。它由感知器、驱动器和信息处理器构成。其设计基础是材料复合的非线性效应，设计原理是相变过程中不同物理量之间的能量转换机制。目前已开发出了形状记忆、压电、电流变体及光纤等类型的智能材料。本文论述了智能材料的基本构成、设计原理、合成方法及其应用，探讨了该材料今后的发展方向。     

Microscopic study on stress-strain relation of granular materials

A biaxial shearing test on granular materials is numerically simulated by distinct element method （DEM）. The evolution of the microstructures of granular materials during isotropic compression and shearing is investigated, on which a yield function is derived. The new yield function has a similar form as the one used in the modified Cam-clay model and explains the yield characteristics of granular materials under the isotropic compression and shear process through the change of the contact distribution N（θ） defining the contacts at particle contact angle θ.     

结构的三维非线性界面元分析

评价了用于含软弱夹层岩体弹塑性分析时常用的Ｇｏｏｄｍａｎ单元及其变形形式的单元。结合界面元法的特点，在单元交界面上引入了能模拟材料弹性及塑性变形的弹簧及滑块元件，使界面元法很好地解决了材料的弹塑性分析而无需另设置任何形式的夹层单元。文中导出了反映层状岩体横观各向同性材料的界面应力公式和非线性界面元的计算公式，并制了相应的计算程序。数值考题表明，将界面元法用于材料的非线性分析，尤其对含有各种节理面的     

High-frequency characterization of an optical phase modulator with phase modulation-to-intensity modulation conversion in dispersive fibers

We propose a new method for characterizing optical phase modulators based on phase modulation-to-intensity modulation (PM-to-IM) conversion in dispersive fibers.The fiber dispersion spectrally alters the relative phasing of the phase-modulated signal and leads to the PM-to-IM conversion,which is extended to measure the modulation efficiency of optical phase modulators.In the demonstration,the frequency-dependent modulation index and half-wave voltage are experimentally measured for a commercial phase modulator.Compared with conventional methods,the proposed method works without the restriction of small-signal operations,and allows swept-frequency measurement with high resolution and accuracy by using a vector network analyzer.     

PZTS凝胶玻璃的结构及光学非线性特性

采用溶胶凝胶工艺，在低温下合成了大量含有铁电相和玻璃相各种组元的ＰＺＴＳ凝胶玻璃．利用Ｘ射线衍射和红外吸收光谱分析手段研究了凝胶玻璃的结构、相变和析晶过程．揭示了低含量凝胶玻璃中的ＺｒＯ２相变的纳米小尺寸效应．最后采用简并四波混频技术研究了透明ＰＺＴＳ凝胶玻璃的三阶非线性光学特性．结果表明，此类材料具有良好的非线性光学特性     

基于非线性波导四波混频的波长变换技术

对光纤四波混频(FWM)效应的机理及相位匹配条件进行了分析,讨论了两种利用FWM进行波长变换的方案：在零色散波长附近利用相位匹配实现波长变换和利用泵浦光强度的非线性效应来实现宽带波长变换．探讨了此项技术目前存在的问题：入射光与泵浦光的偏振态不匹配;信号和泵浦之间的相干程度．提出采用短的高非线性光纤是一种有效的解决方法．     

紫外非线性光学晶体K2Al2B2O7混频特性分析

研究了新型紫外非线性光学晶体K2Al2B2O7(KABO)的频率变换特性,从理论上分析了KABO晶体混频相位匹配角、有效非线性系数、光波走离角、允许角和允许波长等参量与光波长参数之间的关系.这对新型KABO晶体用于产生紫外激光的实验研究提供了理论依据.     

Shock wave on materials

Shock wave is associated with dynamic loading that can result in phase transition（PT）, optical and mechanical property changing, and chemical reaction on materials. Here, we report recent progress about shockinduced PT of polycrystalline iron, the underlying mechanism of the optical emission from sapphire, and the synthesis from single-phase Ru Si in the National Key Laboratory of Shock Wave and Detonation Physics.Results indicated that grain boundary（GB） could affect the PT pressure threshold and rate of iron, the pressure threshold decreases with decreasing GB defects, and the PT rate shows a variation with increasing GB size; wavelength-dependent optical emissivity（non-gray-body emission） would be generated that was not revealed previously for shocked sapphire, and the observed luminescence was from the shock-induced shear bands, but without superheating phenomenon; shock compression could be an effective way to synthesis Ru-Si nanocrystals, when the shock pressure was appropriate; and Ru-Si powder could completely transform to fine-grain structure Cs Cl-type RuSi at 40.4 GPa.     

横观各向同性介质中弹性波的交错格式差分解法

基于应力、速度混合变量弹性波方程及广义胡克定律，给出了一种横观各向同性介质中弹性波计算的高精度交错格式差分解法；本方法可适用于高泊松比材料，数值稳定性较好．均匀和非均匀横观各向同性介质中弹性波传播的数值模拟表明，本文方法计算耗时少、精度高，可有效地模拟复杂各向异性介质中弹性波的传播     

Sensitivity gains in chemosensing by lasing action in organic polymers

Societal needs for greater security require dramatic improvements in the sensitivity of chemical and biological sensors. To meet this challenge, increasing emphasis in analytical science has been directed towards materials and devices having highly nonlinear characteristics; semiconducting organic polymers (SOPs), with their facile excited state (exciton) transport, are prime examples of amplifying materials. SOPs have also been recognized as promising lasing materials, although the susceptibility of these materials to optical damage has thus far limited applications. Here we report that attenuated lasing in optically pumped SOP thin films displays a sensitivity to vapours of explosives more than 30 times higher than is observed from spontaneous emission. Critical to this achievement was the development of a transducing polymer with high thin-film quantum yield, a high optical damage threshold in ambient atmosphere and a record low lasing threshold. Trace vapours of the explosives 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) introduce non-radiative deactivation pathways that compete with stimulated emission. We demonstrate that the induced cessation of the lasing action, and associated sensitivity enhancement, is most pronounced when films are pumped at intensities near their lasing threshold. The combined gains from amplifying materials and lasing promise to deliver sensors that can detect explosives with unparalleled sensitivity.