Analysis of radiation-pressure induced mechanical oscillation of an optical microcavity

The theoretical work of Braginsky predicted that radiation pressure can couple the mechanical, mirror eigenmodes of a Fabry-Pérot resonator to its optical modes, leading to a parametric oscillation instability. This regime is characterized by regenerative mechanical oscillation of the mechanical mirror eigenmodes. We have recently observed the excitation of mechanical modes in an ultrahigh Q optical microcavity. Here, we present a detailed experimental analysis of this effect and demonstrate that radiation pressure is the excitation mechanism of the observed mechanical oscillations.     

Y模型四能级原子辅助光力学系统的多稳现象

本文对Y模型四能级原子辅助光力学系统的稳态特性进行了研究.结果发现,构成复合光力学系统的振动腔镜和被束缚在腔内的原子系综将随着弹簧劲度系数的减小,由单稳态过渡到多稳态.在劲度系数很大时,振动腔镜对整个光力学系统几乎无作用,光力学系统和处在腔中的原子系综都将出现一个稳态解.而当劲度系数足够小时,振动腔镜的稳态位移出现了多稳现象,随之对处于光力学腔中的原子系综的稳态行为也产生了影响,不但使得原子系综的极化率呈现出多个稳态解,同时使得腔中的原子系综对探测光的吸收和色散也发生了相应的变化.同时发现,通过调节劲度系数的取值可以控制整个系统稳态解的个数.这些研究结果在精密测量或量子信息处理等方面具有潜在应用价值.     

Acoustic waves of GaN nitride nanowires

Acoustic waves of GaN nanowires are studied. The materials have a wurtzite structure and thus the elastic anisotropy is included. We use the xyz-algorithm originally employed in the analysis of resonant ultrasound spectroscopy results. We have considered hexagonal cross-section nanowires as those experimentally grown. We have studied also circular cross-section nanowires (nanotubes) for comparison. It was found that the lower frequency modes have a very similar dispersion relation both in shape and frequency value, but higher frequency modes exhibit more important differences. The nanowires are solid or hollow and the influence of the thickness on the dispersion relation and the elastic displacement pattern is considered. Nanowires with a zinc-blende structure have also been considered because of theoretical studies allowing for their existence. We have studied also the squared displacement vectors to see the spatial distribution of the different modes in the nanowires. It was found that there are many modes whose elastic displacement components concentrate around the borders of the nanowire and they do not penetrate almost in the inner part of the nanowire.     

Normal incidence Raman scattering enhancement in double-cavity microresonators

We report on the observation of huge enhancements of the Raman scattering efficiency at quasi-backscattering due to double optical resonances in a microcavity. The structure, based on a double-cavity configuration separated by a central mirror, was specifically designed and grown by molecular beam epitaxy to achieve a large splitting, close to the energy of the LO phonon of GaAs, between the two confined photon modes.     

Spatial distribution of spin-wave modes in cylindrical nanowires of finite aspect ratio

The spin-wave modes of cylindrical nanowires of moderate diameter-to-length ratios are investigated in this paper. Based on three-dimensional simulations and analytical calculations we determine the spatial structures of the modes. We show that standing spin waves and localized edge modes form the discrete spectrum of the nanowires. Using a simple analytical model we infer an extended dispersion relation for spin waves in cylinders. Considering the variation of the demagnetizing (internal) field we show that the localized dipole-exchange modes at the edges are always present.     

共轴环光子晶体的缺陷微腔特性

 采用数值计算方法,模拟了共轴环光子晶体缺陷微腔的谐振模式场分布,计算了此微腔的品质因数和功率损耗,并分析其几何参数对谐振特性的影响。以此缺陷微腔为基础构建周期性慢波系统,讨论了该系统的色散特性。结果表明,微腔中能够存在单一的谐振模式,微腔的纵向长度和介质环介电常数对谐振特性影响较大。所构建的慢波系统有较宽的慢波频域,且慢波比曲线较为平坦。增大电子注开孔半径和减小周期长度对于提高工作频率及增加带宽较为有效。     

Terahertz plasmon and surface-plasmon modes in cylindrical metallic nanowires

We present a theoretical study on collective excitation modes associated with plasmon and surface-plasmon oscilla- tions in cylindrical metallic nanowires. Based on a two-subband model, the dynamical dielectric function matrix is derived under the random-phase approximation. An optic-like branch and an acoustic-like branch, which are free of Landau damp- ing, are observed for both plasmon and surface-plasmon modes. Interestingly, for surface-plasmon modes, we find that two branches of the dispersion relation curves converge at a wavevector qz = qrnax beyond which no surface-plasmon mode exists. Moreover, we examine the dependence of these excitation modes on sample parameters such as the radius of the nanowires. It is found that in metallic nanowires realized by state-of-the-art nanotechnology the intra- and inter-subband plasmon and surface-plasmon frequencies are in the terahertz bandwidth. The frequency of the optic-like modes decreases with increasing radius of the nanowires, whereas that of the acoustic-like modes is not sensitive to the variation of the radius. This study is pertinent to the application of metallic nanowires as frequency-tunable terahertz plasmonic devices.     

Isotropic photonic bandgap in Penrose textured metallic mircocavity

Photonic microcavity has modified photonic modes that have intense localized electric field, which can couple strongly with the embedded emission centers. In this work, we fabricated 2D photonic microcavities with Penrose quasicrystal pattern with 10-fold symmetry. Organic luminescence material tris(8-hydroxyquinoline) aluminum (Alq₃) was embedded into the microcavity and the angle resolved transmission (ART) and photoluminescence (ARPL) spectra of the microcavity were measured. The results showed that the normal Gaussian photoluminescence spectrum of Alq₃ has been strongly modified by the microcavity dispersion characteristic. In addition, omni-directional photonic band gap exists in the microcavity. The higher symmetry of Penrose quasicrystal pattern means that there was minimal difference in the directional dispersion characteristics.     

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.     

Single-frequency coupled asymmetric microcavity laser

Single-mode lasing from a coupled asymmetric microcavity is achieved. By coupling two size mismatched circular microrings to form a coupled asymmetric microcavity, multi-whispering-gallery modes are successfully suppressed and single-frequency laser emission is robustly obtained. Moreover, the laser emits in four directions, and each beam has a divergence of only 6.6 degrees . It is demonstrated further that this single-frequency coupled microcavity laser can be easily integrated with planar lightwave circuits. We provide an easily accessible approach to achieve a single-frequency laser from microcavity lasers operating on whispering-gallery modes.     

Standing optical phonons in finite semiconductor superlattices studied by resonant Raman scattering in a double microcavity

We report optical double resonant enhancement of Raman scattering in a new double microcavity geometry. The design allows almost backscattering geometries, providing easy access to the excitations' in-plane dispersion. The cavity is used to study the phonon spectra of a finite GaAs/AlAs superlattice. A new type of "standing optical vibration" is demonstrated involving the GaAs confined phonons with a standing wave envelope determined by the superlattice thickness. A strong dispersion of the first order standing wave mode is observed, as well as its anticrossing with higher order confined modes of the same symmetry.     

Growth, modulation and photoresponse characteristics of vertically aligned ZnO nanowires

Vertically aligned, c-axis oriented zinc oxide (ZnO) nanowires were grown on Si substrate by metal organic chemical vapor deposition (MOCVD) technique, where sputtered aluminum nitride (AlN) film was used as an intermediate layer and thermally evaporated barium fluoride (BaF₂) film as a sacrificial layer. The aspect ratio and density of the nanowires were also varied using only Si microcavity without any interfacial or sacrificial layer. The UV detectors inside the microcavity have shown the higher on-off current ratio and fast photoresponse characteristics. The photoresponse characteristics were significantly varied with the aspect ratio and the density of nanowires.     

Subpicosecond pulse generation from a 1.56 μm mode-locked VECSEL

Near-transform-limited subpicosecond pulses at 1.56 μm were generated from an optically pumped InP-based vertical-external-cavity surface-emitting laser (VECSEL) passively mode-locked at 2 GHz repetition rate with a fast InGaAsNSb/GaAs semiconductor saturable absorber mirror (SESAM). The SESAM microcavity resonance was adjusted via a selective etching of phase layers specifically designed to control the magnitude of both the modulation depth and the intracavity group delay dispersion of the SESAM. Using the same VECSEL chip, we observed that the mode-locked pulse duration could be reduced from several picoseconds to less than 1 ps with a detuned resonant SESAM.     

Deterministic and replaceable transfer of silver flakes for microcavities

How to fabricate high-quality microcavities simply and at low cost without causing damage to environmentally sensitive active layers such as perovskites are crucial for the studies of exciton−polaritons, however, it remains challenging in the field of microcavity fabrication. Usually, once the top mirror is deposited, the detuning of the microcavity is fixed and there is no easy way to tune it. Here, we have developed a method for deterministically transferring silver mirrors, which is relatively simple and guarantees the active layer from damaging of high temperature, particle bombardment, etc., during the deposition of the top mirror. Furthermore, with the help of a glass probe, we demonstrate a replaceable silver transfer method to tune the detuning of the microcavity, thereby changing the coupling of photons and excitons therein. The developed deterministic and replaceable silver mirror transfer methods will provide the capability to fabricate high-quality and tunable microcavities and play an active role in the development of the exciton−polariton field.     

Stability of second harmonic minority heating in magnetic mirror systems

A dispersion relation has been derived to study the stability of ion cyclotron (IC) propagation at the second harmonic of the minority component deuterium in a mirror confined plasma that has hydrogen as the majority species. We have worked in the frame of the majority ions; our dispersion relation can thus be used to study IC propagation in a single ion plasma also. Analysis of the dispersion relation yields two modes — one below and the other above the ion gyro-frequency Θ_H of hydrogen. The expression for the growth rate is used to explicitly show that an instability can arise in the plasma when the loss-cone indexj⩾3; this instability being a result of the coalescing of the two modes supported by the plasma. Unfortunately, the minority component deuterium does not decrease this instability and thus the proposed scheme of IC heating at the second harmonic of the minority component seems unsuited to mirror devices.     

Exciton polaritons confined in a ZnO nanowire cavity

Semiconductor nanowires of high purity and crystallinity hold promise as building blocks for miniaturized optoelectrical devices. Using scanning-excitation single-wire emission spectroscopy, with either a laser or an electron beam as a spatially resolved excitation source, we observe standing-wave exciton polaritons in ZnO nanowires at room temperature. The Rabi splitting between the polariton branches is more than 100 meV. The dispersion curve of the modes in the nanowire is substantially modified due to light-matter interaction. This finding forms a key aspect in understanding subwavelength guiding in these nanowires.     

Optimization of microcavity OLED by varying the thickness of multi-layered mirror

We optimized the emission efficiency from a microcavity OLEDs consisting of widely used organic materials, N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq₃) as emitting and electron transporting layer. LiF/Al was used as a cathode, while metallic Ag was used as an anode material. A LiF/NPB bi-layer or NPB layer on top of the cathode was considered to alter the optical properties of the top mirror. The electroluminescence emission spectra, electric field distribution inside the device, carrier density, recombination rate and exciton density were calculated as a function of the position of the emission layer. The results show that for optimal capping layers thicknesses, light output is enhanced as a result of the increase in both the reflectance and transmittance of the top mirror. Once the optimum structure has been determined, the microcavity OLED devices were fabricated and characterized. The experimental results have been compared to the simulations and the influence of the thickness of the mirror layers, emission region width and position on the performance of microcavity OLEDs was discussed.     

Unidirectional high intensity narrow-linewidth lasing from a planar random microcavity laser

Lasing was achieved in a new type of random laser: the planar random microcavity laser. The laser consists of a planar microcavity with a random gain layer. Optical confinement by the two-dimensional random cavity and the one-dimensional planar microcavity drastically reduces the number of resonant modes. As a result, the laser output is highly directional (the divergence angle is 1.68 degrees) with an extremely narrow-linewidth and ultralow threshold. All these phenomena are explained in terms of the coupling of random cavity modes and planar microcavity modes. The results demonstrate an important step towards applications of random lasers.     

Motional narrowing in semiconductor microcavities

We describe experiments on a semiconductor microcavity which provide the first demonstration of motional narrowing in semiconductor inter-subband optical transitions. Significant narrowing occurs because of the small mass of the polaritons in a microcavity. The demonstration is made possible by the control provided in a microcavity of the mixing between photon and exciton states, and hence the dispersion of the polariton.     

电致发光色纯性增强的硅基有机微腔

报道了硅基有机微腔的电致发光（EL）.该微腔由上半透明金属膜、中心有源多层膜和多孔硅分布Bragg反射镜（PS DBR）组成.半透明金属膜由Ag（２０nm）构成，充当发光器件的负电极和微腔的上反射镜.有源多层膜由Al (1 nm) / LiF(05 nm) /Alq3/Alq3:DCJTB/NPB/CuPc/ITO/SiO2组成，其中的Al/LiF为电子注入层，ITO为正电极，SiO2为使正、负电极电隔离的介质层.该PS DBR是采用设备简单、成本低廉且非常省时的电化学腐蚀法用单晶Si来制备的；该PS 关键词： 电化学腐蚀 电致发光 窄峰发射 硅基有机微腔