Direct observation of whispering gallery mode polaritons and their dispersion in a ZnO tapered microcavity

We report direct observation of the strong exciton-photon coupling in a ZnO tapered whispering gallery (WG) microcavity at room temperature. By scanning excitations along the tapered arm of the ZnO tetrapod using a micro-photoluminescence spectrometer with different polarizations, we observed a transition from the pure WG optical modes in the weak interaction regime to the excitonic polariton in the strong coupling regime. The experimental observations are well described by using the plane wave model including the excitonic polariton dispersion relation. This provides a direct mapping of the polariton dispersion, and thus a comprehensive picture for coupling of different excitons with differently polarized WG modes.     

Effects of Strong Turbulence on the Spiral Plane Mode of Whittaker-Gaussian Beam through Terrene-Atmosphere

The analytic formulae of probability distribution of spiral plane modes for the Whittaker-Gaussian(WG) beams with orbital angular momentum(OAM) in strong turbulence regime are modeled based on the modified Rytov approximation.Numerical results show that the crosstalk range of OAM modes in the vicinity of signal mode increases with the increasing refractive-index construction parameter.However,effects of change of the width of the Gaussian envelope and the parameter Wo of WG beams on normalization energy weight of signal mode can be ignored.We find theoretically that signal spiral plane mode of WG beams at each OAM level approximatively has the same normalization energy weight,inaplying that the channels with WG(pseudo non-diffraction) beam have higher channel capacity than the channels with the Laguerre-Gaussian beam.     

一维金属光栅嵌入磁性介质纳米结构下的横向磁光克尔效应的增强

本文在一维金属光栅嵌入磁性介质的体系中实现了横向磁光克尔效应的增强.通过最优化金属光栅的嵌入深度来有效激发磁性介质中的波导模式与金属条带上的局域等离激元模式,从而使横向磁光克尔效应的响应得到巨大增强.本文提出了一种用于增强横向磁光克尔效应的新型等离激元微纳结构,这种结构可以应用于高性能磁光器件的设计.     

Amplification and saturation in a CO2 waveguide amplifier

An ir CO₂, dc current pumped, optical waveguide (WG) amplifier has been built, and its active medium optical parameters measured for several CO₂ emission lines, and their dependence from active medium total pressure, discharge current and temperature was investigated.High gain is found which, coupled with relatively high saturation power in the WG fundamental mode and ease of fabrication with this technology in long (up to 1.5 m) lengths, indicates promising use to efficiently amplify high spectral and spatial purity output of a short, highly tunable WG laser up to power levels suited for nonlinear spectroscopy and optical pumping. The dependence of the small signal gain coefficient and of the saturation parameter for individual rotational lines on the radiation intensity was computed using experimentally known parameters of the discharge plasma. The computation was carried out using the two mode rate equation approach for CO₂–N₂–He gas mixtures. A satisfactory agreement between theoretical and experimental results was obtained.Work supported by G.N.S.M.-C.N.R. and M.P.I.     

WG-Like Modes Selectivity in a Square Cavity with Posts

We investigate the characteristics of Whispering-Gallery（WG）-like modes in a square cavity with posts by employing the two-dimensional （2D） finite-difference time-domain （FDTD） technique combined with the effective index method. The results indicate that the posts can result in mode selection in the WG-like modes. The WG-like modes with odd mode numbers are not much sensitive to the sizes of the posts. However, the quality factor （i.e. Q-factor） of the WG-like modes with even mode numbers decreases sharply with the increasing size of the posts. The decreasing Q-factor is attributed to mode leakage and scattering loss due to the presence of the post. The mode selection increases the mode spacing of square cavity twice in an optimized structure.     

Optical modes in semiconductor microtube ring resonators

We demonstrate optical modes in InGaAs/GaAs microtubes acting as optical ring resonators. Self-supporting microtubes were fabricated by optical lithography and wet-etching processes utilizing the self-rolling mechanism of strained bilayers. The optical modes were probed by the photoluminescence of InAs quantum dots embedded in the tube's wall. In this novel microtube ring resonator we find a spectrum of sharp modes. They are in very good agreement with the theoretical results for a closed thin dielectric waveguide.     

Highly efficient design of spectrally engineered whispering-gallery-mode microlaser resonators

We present an accurate, reliable and versatile method for studying the effect of deformations on the characteristics of the high-Q whispering gallery (WG) modes supported by two-dimensional dielectric resonators (DR). An eigenvalue problem is formulated in terms of contour integral equations and further discretised with the method of analytical regularisation. Such a procedure significantly reduces the number of unknowns whilst providing high and controllable accuracy. Natural frequencies, Q-factors and field patterns of elliptical, flower- and egg-shaped DRs are calculated. Methods to enhance the Q-factors, provide directional light output, and parasitic mode suppression are discussed. The identification of WG modes is simplified by the symmetrical/asymmetrical mode separation included into the formulation of the problem and solution algorithm.     

Acoustic field excited by a pulsed laser line source in a cylinder

The excitation and propagation of the acoustic waves in an elastic cylinder are studied by laser ultrasonics both theoretically and experimentally. The theoretical analysis of the two-dimensional acoustic field excited by a pulsed laser line source impacting on the generatrix of an elastic cylinder is presented. The dispersive properties for both cylindrical Rayleigh wave and the higher modes--whispering gallery (WG) modes are analyzed in detail. The numerical transient displacement waveforms for a detecting point located another terminal of the cylinder diameter opposite the source are calculated. The experimental excitation and detection of the acoustic waves in an aluminum cylinder are carried out on a laser ultrasonic system, which mainly consists of a Q-switched Nd:YAG laser and a laser interferometer. The wave components of bulk waves and surface waves (cylindrical Rayleigh waves and WG modes) are analyzed by comparing the numerical and experimental waveforms. The results are in good agreement.     

Mathematical study of the two-dimensional lasing problem for the whispering-gallery modes in a circular dielectric microcavity

Microdisk lasers are investigated for their thresholds characteristics. We present a novel approach for studying the threshold gains of the whispering-gallery (WG) and other modes based on solving the boundary value problem for the Maxwell's equations. The novelty is that we consider the real-value pairs of frequencies and material gains as eigenvalues. In the two-dimensional (2D) approximation this problem is reduced to the set of independent transcendental equations. A Newton's method is further used to calculate the thresholds and natural frequencies numerically.     

Photoluminescence from site-selected coupling between quantum dots and microtoroid cavities

By using CdSe/ZnS quantum dots （QDs）, we study the effect of cavity quantum electrodynamics on the coupling of the microtoroid cavity. When with whispering gallery （WG） modes, the microtoroid cavity demonstrates high quality factor and small mode volume at visible wavelengths. Accordingly, fiber tapers allow QDs to adhere into the cavity and further permit the control of site-selected coupling. From the luminescence spectra, QDs are modulated effectively by cavity modes, Variable modulations are observed by changing QD coupling conditions. Therefore, based on experimental and theoretical research, strong and tunable Purcell enhancement can be realized by this system.     

Optomechanical coupling in a two-dimensional photonic crystal defect cavity

Periodically structured materials can sustain both optical and mechanical modes. Here we investigate and observe experimentally the optomechanical properties of a conventional two-dimensional suspended photonic crystal defect cavity with a mode volume of ~3(λ/n)3. Two families of mechanical modes are observed: flexural modes, associated to the motion of the whole suspended membrane, and localized modes with frequencies in the GHz regime corresponding to localized phonons in the optical defect cavity of diffraction-limited size. We demonstrate direct measurements of the optomechanical vacuum coupling rate using a frequency calibration technique. The highest measured values exceed 80 kHz, demonstrating high coupling of optical and mechanical modes in such structures.     

The optical nonreciprocal response based on a four-mode optomechanical system

We propose a scheme for realizing the optical nonreciprocal response based a four-mode optomechanical system,consisting of two charged mechanical modes and two linearly coupled optical modes. Two charged mechanical modes are coupled by Coulomb interaction, and two optical modes are coupled to one of mechanical modes by radiation pressure. We numerically evaluate the transmission probability of the probe field to obtain the optimum optical nonreciprocal response parameters. Also, we show that the optical nonreciprocal response is caused by the quantum interference between the optomechanical couplings and the linearly coupled interaction that breaks the time-reversal symmetry.     

Electron-phonon interaction in hemispherical quantum dot

Within the framework of the dielectric continuum (DC) model, the optical phonon modes and electron-optical-phonon interaction in hemispherical quantum dot are investigated. The proper eigenfunctions for longitudinal optical (LO) and interface optical (IO) phonon modes are constructed. After having quantized the eigenmodes, we derive the Hamiltonian operators describing the LO and IO phonon modes as well as the corresponding Fröhlich electron-phonon interaction. The dispersion relation of IO phonon modes is size independent. The potential applications of these results are also discussed.     

Lagrangian approach for analysis of radiation pressure induced parametric instability in micro-resonators

We introduce a new scheme for determining radiation pressure coupling to microresonator devices. It is shown that for the input pump powers there exists a threshold value for instability behavior. Radiation pressure can couple mechanical modes of a cavity to it's optical modes, leading to parametric oscillation instability. Here we present an approximate analysis of such nonlinear effect with Hamilton's least action principle. Our Lagrangian includes no interaction term, but interaction between optical and mechanical modes has been taken into account through integration limit.     

Leaky Modes in Ag Nanowire over Substrate Configuration

By launching surface plasmons propagating along the Ag nanowire deposited on a substrate, we clearly observe three leaky modes using the Fourier imaging method. The effective refractive indexes, propagation lengths and electric field distributions of the modes are investigated, which indicate that the energy of the mode with a lowest effective refractive index is mainly distributed in the air, while for the other two modes, it is mainly distributed in the substrate and in the gap between the Ag nanowire and the substrate. These modes enable such a configuration to be used as a multichannel waveguide or highly directional optical antenna, which is of fundamental importance for optical device miniaturizations and photonic circuit integrations.     

Brillouin propagation modes in optical lattices: interpretation in terms of nonconventional stochastic resonance

We report the first direct observation of Brillouin-like propagation modes in a dissipative periodic optical lattice. This has been done by observing a resonant behavior of the spatial diffusion coefficient in the direction corresponding to the propagation mode with the phase velocity of the moving intensity modulation used to excite these propagation modes. Furthermore, we show theoretically that the amplitude of the Brillouin mode is a nonmonotonic function of the strength of the noise corresponding to the optical pumping, and discuss this behavior in terms of nonconventional stochastic resonance.     

Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides

We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton(SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding.With Maxwell's equations and Maxwell stress tensor,we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides.The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters.Importantly,an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation.These special optical properties will open the door for potential optomechanical applications,such as optical tweezers and actuators.     

Quantum fluctuations of a vortex in an optical lattice

Using a variational ansatz for the wave function of the Bose-Einstein condensate, we develop a quantum theory of vortices and quadrupole modes in a one-dimensional optical lattice. We study the coupling between the quadrupole modes and Kelvin modes, which turns out to be formally analogous to the theory of parametric processes in quantum optics. This leads to the possibility of squeezing vortices. We solve the quantum multimode problem for the Kelvin modes and quadrupole modes numerically and find properties that cannot be explained with a simple linear-response theory.     

Gilbert damping in the layered antiferromagnet CrCl3

We theoretically and experimentally studied the Gilbert damping evolution of both acoustic and optical magnetic resonance modes in the layered flake Cr Cl;with an external magnetic field H applied in plane.Based on a Lagrangian equation and a Rayleigh dissipation function,we predicted that the resonance linewidth△H as a function of microwave frequencyωis nonlinear for both acoustic and optical modes in the Cr Cl;flake,which is significantly different from the linear relationship of△H-ωin ferromagnets.Measuring the microwave transmission through the Cr Cl;flake,we obtained theω–H dispersion and damping evolution△H–ωfor both acoustic and optical modes.Combining both our theoretical prediction and experimental observations,we concluded that the nonlinear damping evolution△H–ωis a consequence of the interlayer interaction during the antiferromagnetic resonance,and the interlayer Gilbert dissipation plays an important role in the nonlinear damping evolution because of the asymmetry of the non-collinear magnetizaiton between layers.     

三机械薄膜腔光力系统相互作用的研究

本文主要研究了利用传输矩阵理论和共振透射条件详细地推导光腔中均匀放置三个机械薄膜构成的腔光力系统中系统本征模式随机械运动的色散关系.计算结果发现系统的光学本征模式由一组四个的本征能级构成,且不同的能级随不同的机械运动模式的变化曲线各不相同,进而导致不同光学模式与不同机械运动模式之间的耦合也不相同.此外,利用微扰理论求解了当机械运动振幅远小于腔模波长、机械振子处于平衡位置附近时,各种光学模式与不同机械振动模式间相互作用耦合强度的解析表达式.研究结果能够为理论和实验上研究多模腔光力系统提供一定的参考.