Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.     

Imaging single quantum dots in three-dimensional photonic crystals

Performing fluorescence wide-field microscopy we have imaged single semiconductor quantum dots deep inside a 3-dimensional photonic crystal prepared from colloidal polymer beads. Exploring the emission diffraction patterns in defocused images of quantum dots we demonstrate that the direction-dependent photonic stop band imprints an anisotropy to the angular emission of a single quantum dot. Hence a single, quasi-point-like emitter is manipulated to radiate its photons only to certain well-defined directions by means of the anisotropic light propagation in photonic crystals. The experiments thus provide new routes to evaluate local, frequency selective optical properties in 3-dimensional photonic crystals employing single emitters.     

Enhanced optical nonlinearity near the photonic bandgap edges of a cholesteric liquid crystal

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.     

Structure of polarization-resolved conoscopic patterns of planar oriented liquid crystal cells

The geometry of distributions of the polarization of light in conoscopic patterns of planar oriented nematic and cholesteric liquid crystal (LC) cells is described in terms of the polarization singularities including C-points (points of circular polarization) and L lines (lines of linear polarization). Conditions for the formation of polarization singularities (C-points) in an ensemble of conoscopic patterns parametrized by the polarization azimuth and ellipticity of the incident light wave have been studied. A characteristic feature of these conditions is selectivity with respect to the polarization parameters of the incident light wave. The polarization azimuth and ellipticity are determining parameters for nematic and cholesteric LC cells, respectively.     

Polarization dependent guiding in liquid crystal filled photonic crystal fibers

A theoretical study of nematic liquid crystal filled photonic crystal fibers (LCPCFs) is presented. Detailed investigations including the polarization dependent bandgap formation and the modal properties are given for LCPCFs, in which alignment of the molecules could be controlled by external static electric field. The polarization dependent bandgap splitting caused by the high index difference between the ordinary and the extraordinary dielectric index of nematic liquid crystals provides the possibility of single-mode single-polarization guiding. A polarization operation diagram is proposed to describe the guiding behavior of LCPCFs. The influence of rotation angle ? of the director of liquid crystals on the modal properties is investigated. It is shown that the polarization axis of the guided mode is determined by the rotation angle ?, which could be controlled by external electric field.     

Temperature tuning of polarization mode dispersion in single-core and two-core photonic liquid crystal fibers

In this paper we present numerical and experimental results of propagation and polarization properties of the photonic liquid crystal fibers (PLCFs) in which only selected micro holes were filled with nematic liquid crystal (LC) guest materials. As a host photonic crystal fiber (PCF) structure, we used a commercially available highly birefringent PCF (Blazephotonics, UK). A tunable laser operated at infrared has powered the PLCFs under investigation infiltrated by the 1550 nematic LC synthesized at the Military University of Technology. Temperature induced changes of the polarization mode dispersion (PMD) as well switching between fundamental and higher order modes and also single-core and two-core propagation were successfully demonstrated.     

Polarization-universal bandgap in periodically twisted nematics

Cholesteric liquid crystals are known to possess bandgap and exhibit strong reflection for one of two circular polarizations of light. We suggest a periodically twisted nematic liquid crystal as a medium, which possesses bandgap and exhibits strong reflection for any polarization of normally incident light. Two possible structures are considered: a sinusoidal modulation profile and a rectangular modulation profile. In both cases, the maximum bandgap of a periodically twisted structure is approximately twice as narrow as that of cholesterics. However, the polarization properties of these structures may make them more advantageous than cholesterics in a variety of applications.     

二维光子晶体量子阱的光谱特性研究

研究了二维光子晶体量子阱的光谱特性,该量子阱结构由二维正方晶格圆柱晶胞光子晶体通过移去中间位置的介质圆柱层形成。由于光子晶体中的光子禁带充当了光子运动的势垒,类似于半导体量子阱中电子的行为,在光子晶体量子阱结构中会出现量子化的光子能态。文章利用平面波展开法计算了所用光子晶体的能带结构,利用传输矩阵方法计算了量子阱结构的透射光谱。计算结果表明,在光子禁带中出现了离散的透射峰,透射峰的强度随着势垒宽度的增加而减弱,个数随着势阱宽度的增加而增加,通过计算得到了其定量关系,并且讨论了透射峰频率与势阱宽度的关系。     

Creation of tunable absolute bandgaps in a two-dimensional anisotropic photonic crystal modulated by a nematic liquid crystal

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable absolute bandgap in a two-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic-dielectric cylinder in the liquid crystal medium is studied by solving Maxwell's equations using the plane wave expansion method. The photonic band structures are found to exhibit absolute bandgaps for the square and triangular lattices. Numerical simulations show that the absolute bandgaps can be continuously tuned in the square and triangular lattices consisting of anisotropic-dielectric cylinders by infiltrating nematic liquid crystals. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits.     

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.     

偶极子位置及偏振对激发光子晶体H1微腔的影响

光子晶体微腔和量子点的集成是实现量子信息处理非常具有潜力的平台之一,利用微腔和量子点的耦合可以制备纠缠光子对,实现对量子态的操控.因为光子晶体微腔具有品质因子高、模场体积小等优点,可以极大地增强光与物质之间的相互作用,从而易于实现量子态在不同物理体系之间的转换.通过单量子点和光子晶体H1微腔的耦合可以产生纠缠光子对,因为H1微腔具有简并的、模式偏振正交的基态模式.通常微腔模式的激发随着量子点在微腔中的位置变化而改变,本文用时域有限差分方法研究了偶极子光源的位置及偏振对激发光子晶体H1微腔模式的影响.结果表明:通过改变偶极子光源位置可以选择性地激发H1微腔简并模式中的一个;具有某一偏振的偶极子光源只能激发相应偏振的微腔模式;模式激发强度的大小也是由偶极子光源在微腔中的位置决定的.鉴于目前量子点在微腔中的位置尚不能精确控制,所以微腔模式受激发光源位置的影响的研究具有重要意义.     

染料掺杂聚合物分散胆甾相液晶薄膜激光特性研究

采用激光染料DCM、向列相液晶TEB30A、手性剂S-811、聚乙烯醇(PVA), 通过微胶囊法制备了聚合物分散胆甾相液晶薄膜, 测量激光辐射谱, 研究了其激光辐射机理和温度调谐特性. 利用正交偏光显微镜观察器件织构, 看到液晶微滴分散均匀, 尺寸较大, 约为80 μm, 并且微滴中液晶分子呈现平面态排列织构. 以532 nm的Nd:YAG固体激光器作为抽运源, 测得在634.5 nm和680.2 nm波长处出现了尖锐的激光辐射峰, 线宽分别约为0.25 nm, 0.29 nm. 并与染料掺杂胆甾相液晶激光器件进行比较. 升高器件温度, 其输出激光波长蓝移, 获得666.7 nm至643.9 nm共22.8 nm的调谐范围. 由实验结果分析得出, 激光辐射机理为光子禁带末端激光, 出射波长分别对应光子禁带的两个边沿.     

Defect mode emission of a dye doped cholesteric polymer network

We have observed enhanced fluorescence and laser emission due to a photonic defect mode in a dye doped cholesteric polymer network. The defect is caused by a phase jump of the cholesteric helix at the interface of two stacked layers of a cholesteric polymer film. Fluorescence spectra show an additional resonant mode inside the photonic stop band. Pulsed excitation gives rise to laser emission of the defect mode, with an exceptionally low lasing threshold. The defect mode emission has a circular polarization whose sense of rotation is opposite to that of the cholesteric helix.     

Continuous wave mirrorless lasing in cholesteric liquid crystals with a pitch gradient across the cell gap

Despite numerous efforts, continuous wave (CW) lasing in dye doped, one-dimensional (1D) photonic bandgap cholesteric liquid crystal (CLC) structures has not been previously reported, to our knowledge. Here we report on the observation of lasing in such structures under both coherent (laser) and incoherent (LED) CW light excitation. To achieve this effect, we used a 1D-photonic bandgap structure made of a polymer stabilized CLC with a pitch gradient across the cell thickness. A spectral reflectivity profile of such a CLC structure reveals local minima in the area within a photonic stopband and close to it. The realization of lasing pumped by low power CW light sources opens the possibility of all-organic, compact, tunable CW lasers for display and medical applications.     

Fast path and polarization manipulation of telecom wavelength single photons in lithium niobate waveguide devices

We demonstrate fast polarization and path control of photons at 1550?nm in lithium niobate waveguide devices using the electro-optic effect. We show heralded single photon state engineering, quantum interference, fast state preparation of two entangled photons, and feedback control of quantum interference. These results point the way to a single platform that will enable the integration of nonlinear single photon sources and fast reconfigurable circuits for future photonic quantum information science and technology.     

Linearly polarized, single-mode spontaneous emission in a photonic nanowire

We introduce dielectric elliptical photonic nanowires to funnel efficiently the spontaneous emission of an embedded emitter into a single optical mode. Inside a wire with a moderate lateral aspect ratio, the electromagnetic environment is largely dominated by a single guided mode, with a linear polarization oriented along the ellipse major axis. The resulting monomode spontaneous emission is maintained over a broad wavelength range, a key asset of this 1D photonic structure. Our theoretical analysis is completed by an experimental study of GaAs elliptical photonic wires with embedded InAs quantum dots. In particular, the fraction of collected photons with the desired linear polarization can exceed 95%.     

Single-photon emitters in van der Waals materials

Solid-state sources of single-photon emitters are highly desired for scalable quantum photonic applications, such as quantum communication, optical quantum information processing, and metrology. In the past year, great strides have been made in the characterization of single defects in wide-bandgap materials, such as silicon carbide and diamond, as well as single molecules, quantum dots, and carbon nanotubes. More recently, single-photon emitters in layered van der Waals materials attracted tremendous attention, because the two-dimensional(2 D)lattice allows for high photon extraction efficiency and easy integration into photonic circuits. In this review, we discuss recent advances in mastering single-photon emitters in 2 D materials, electrical generation pathways,detuning, and resonator coupling towards use as quantum light sources. Finally, we discuss the remaining challenges and the outlooks for layered material-based quantum photonic sources.     

基于矩阵理论的螺旋液晶透射光偏振态研究

将螺旋型液品看作是N层双折射材料晶片叠合而成,而每层光轴相对于相邻的晶片有一个小的旋转.本文基于矩阵理论,研究了光在螺旋液晶中传输时偏振态的变化.经过详细的数学推导,理论研究表明.线性偏振光经过螺旋液晶后偏振态会发生改变.当满足一定的条件时,线偏振光的偏振方向旋转90°,左旋圆偏振光经过左旋螺旋液晶后转变为右旋圆偏振光.     

向列相液晶缺陷光子晶体透射光谱偏振敏感特性研究

研究了向列相液晶缺陷TiO2和SiO2交替的光学多层膜一维光子晶体透射谱偏振敏感特性。外电压下透射光谱测试和模拟结果显示,对于平行取向的向列相液晶,当自然光垂直入射时,禁带中两处出现e(TE模式)光和o光(TM模式)透射峰,具有偏振敏感性。随着电压增大,e光透射峰蓝移与o光透射峰合二为一,光谱可调谐范围分别为31和34nm;而对于取向混乱的向列相液晶,禁带中两处出现独立的透射峰,无偏振敏感性。随着电压增大峰位也蓝移,光谱可调谐范围分别为64和15nm。通过混乱取向液晶分子,可以使o光和e光有效折射率值相等,获得偏振不敏感特性。     

Angular tuning of defect modes spectrum in the one-dimensional photonic crystal with liquid-crystal layer

A one-dimensional ZrO₂/SiO₂ photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal were shown to split into four polarized components T_ij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths, while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal. The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are in good agreement with the experimental data.