Intense directional lasing from a deformed square-shaped organic-inorganic hybrid glass microring cavity

Intense directional light emission from a deformed square-shaped organic light-emitting microring cavity was observed. The ring cavity was a dye-doped organic-inorganic hybrid glass film coated upon a square-shaped fiber. From the near-field and far-field emission patterns and their emission spectra we found, for the first time to our knowledge, the simultaneous existence of chaotic whispering-gallery modes and four-bounce reflection modes. The two types of mode have different emission directions, different lasing thresholds, and different spectral linewidths. High-contrast angle-modulated light emission was also observed. We could control modulation and angular spread of emission by controlling the deformation of the cavity.     

Classical phase space revealed by coherent light

We study the far-field characteristics of oval-resonator laser diodes made of an GaAs/Al(x)Ga(1-x)As quantum well. The resonator shapes are various oval geometries, thereby probing chaotic and mixed classical dynamics. The far-field pattern shows a pronounced fine structure that strongly depends on the cavity shape. Comparing the experimental data with ray-model simulations for a Fresnel billiard yields convincing agreement for all geometries and reveals the importance of the underlying classical phase space for the lasing characteristics.     

Influence of cavity de-tuning in semiconductor microcavity LEDs

Data are presented showing the precise role of the cavity de-tuning on the emission properties of semiconductor microcavity light emitting diodes (MC-LEDs). Enhanced output power and narrow line width emission have been observed over a wide range of cavity de-tunings, with a power reduction of less than −1 dB observed for ±12 nm de-tuned devices. For a resonantly de-tuned MC-LED, the slope efficiency extracted from the power output versus current characteristics decreases monotonically with increasing temperature. However, for a MC-LED de-tuned +5.6 nm to long wavelength with respect to the room temperature quantum well (QW) peak, the extracted slope efficiencies vary by less than ±0.5 dB over a temperature range of greater than 65°C. Compared to a conventional LED, narrower beam divergence is observed for MC-LEDs de-tuned to short wavelength with respect to the bare QW peak. For positively de-tuned MC-LEDs the beam divergence broadens, and the far-field emission profiles exhibit a double-lobed pattern that is sensitive to pump level.     

Uncertainty-limited turnstile transport in deformed microcavities

We present both experimental and theoretical evidence for uncertainty-limited turnstile transport in deformed microcavities. As the degree of cavity deformation was increased, a secondary peak gradually emerged in the far-field emission patterns to form a double-peak structure. Our observation can be explained in terms of the interplay between turnstile transport and its suppression by the quantum mechanical uncertainty principle.     

Control of spontaneous emission by complex nanostructures

Spontaneous emission in the presence of complex nanostructures is discussed by use of a calculational scheme that permits us to deal with interfaces of arbitrary shape. Control over the field associated with the emission is shown to be attainable. In particular, decay rates are offered for geometries that lead to focusing and collimation of near- and far-field distributions. Emission from axially symmetric gratings is shown to lead to narrow angular distributions of emission, and focusing at the foci of dielectric ellipsoids is achieved for dimensions comparable with the wavelength. In the latter case the total emission rate for two atoms in an ellipsoidal cavity is shown to be enhanced in a way that deviates from the predictions of the Dicke effect by means of intermediate- and far-field contributions.     

Fresnel filtering in lasing emission from scarred modes of wave-chaotic optical resonators

We study lasing emission from asymmetric resonant cavity GaN microlasers. By comparing far-field intensity patterns with images of the microlaser we find that the lasing modes are concentrated on three-bounce unstable periodic ray orbits; i.e., the modes are scarred. The high-intensity emission directions of these scarred modes are completely different from those predicted by applying Snell's law to the ray orbit. This effect is due to the process of "Fresnel filtering" which occurs when a beam of finite angular spread is incident at the critical angle for total internal reflection.     

90% pump depletion and good beam quality in a pulse-injection-seeded nanosecond optical parametric oscillator

We measured 90% pump depletion in a singly resonant image-rotating nanosecond optical parametric oscillator that was pulse-injection seeded by a self-generated signal pulse. The oscillator was pumped by an 8 ns duration single-frequency 532 nm pulse from an injection-seeded Q-switched Nd:YAG laser and resonated an 803 nm signal. The pump and pulsed-seed beams had flat-topped spatial fluence profiles with diameters of approximately 6 mm, giving a cavity Fresnel number at 803 nm approaching 400. The beam cleanup effects of the image-rotating cavity produce a far-field signal spatial fluence profile with approximately 60% of its energy falling within the diffraction-limited spot size.     

Spectral response and far-field pattern of a dipole nano-antenna on metamaterial substrates having near-zero and negative indices of refraction

In this work the resonance, frequency response, and far-field patterns of an optical nano-antenna placed on an interface between air and a metamaterial substrate is obtained through finite element calculations. The metamaterial is characterized by an effective, macroscopic index of refraction which can take negative and near-zero values, or by published values of the effective permittivity and permeability for metamaterials. The results show that the resonant wavelength and response can be fitted to analytical functions that are even functions of the index of refraction, this is consistent with the knowledge that negative indices of refraction allows for wave propagation in the same magnitude but opposite direction observed with positive indices of refraction. The simulations also show that substrates with near-zero index of refraction will enhance the antenna response by 62% compared to substrates with n > 1. Lossy metamaterials are also considered in the simulations. The far-field pattern of the antenna, obtained through a near-field to far-field transformation, behaves the same independently of the sign of the index of refraction, also the far-field pattern for the emission towards near-zero substrates is nearly constant and independent of the angle for the evaluated angular range.     

Linear and non-linear behavior of cavity polaritons

We report on the linear and non-linear emission of cavity-polaritons under resonant excitation. At low excitation density, in addition to polariton photoluminescence, strong Rayleigh scattering is observed. At higher excitation densities, a sudden transition to a highly emissive state is observed, accompanied by spatial patterning. We attribute such phenomena to a combination of nonlinear cavity-polariton relaxation mechanism and nonlinear response of the cavity, leading to transverse pattern formation. A careful analysis of near- and far-field emission patterns with spatial filtering as well as reflectivity shows that an inhomogeneous situation develops, the center of the excited region undergoing a strong to weak coupling transition while the periphery is still in strong coupling. Despite the complex non-linear behavior we observe no signatures of Bose–Einstein condensation or Boser action.     

Photon bunching and anti-bunching with two dipole-coupled atoms in an optical cavity

We investigate the effect of the dipole–dipole interaction(DDI) on the photon statistics with two atoms trapped in an optical cavity driven by a laser field and subjected to cooperative emission. By means of the quantum trajectory analysis and the second-order correlation functions, we show that the photon statistics of the cavity transmission can be flexibly modulated by the DDI while the incoming coherent laser selectively excites the atom–cavity system's nonlinear Jaynes–Cummings ladder of excited states. Finally, we find that the effect of the cooperatively atomic emission can also be revealed by the numerical simulations and can be explained with a simplified picture. The DDI induced nonlinearity gives rise to highly nonclassical photon emission from the cavity that is significant for quantum information processing and quantum communication.     

The role of refocusing in dynamic X-wave formation during femtosecond laser filamentation in water

<正>With the evolution of a laser pulse in water,the formation of a nonlinear X wave during femtosecond filamentation is investigated based on numerical simulations.In particular,we analyze the far-field angularly resolved spectra obtained for different temporal portions of the ultrashort pulse during its propagation. Our result shows that the refocusing of ultrashort pulse leads to the formation of dynamic X wave which essentially manifests itself as conical emission.     

Controlling the spontaneous emission rate of single quantum dots in a two-dimensional photonic crystal

We observe large spontaneous emission rate modification of individual InAs quantum dots (QDs) in a 2D photonic crystal with a modified, high-Q single-defect cavity. Compared to QDs in a bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase of up to a factor of 8. In contrast, off-resonant QDs indicate up to fivefold rate quenching as the local density of optical states is diminished in the photonic crystal. In both cases, we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with a pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using finite difference time domain simulations and find good agreement with experiment.     

External Cavity Tuning of Coherent Quantum Cascade Laser Array Emitting at ～7.6μm

An external cavity quantum cascade laser(QCL)array with a wide tuning range and high output power is presented.The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration.Taking advantage of the single-lobed fundamental supermode far-field pattern,the tuning capability of 30.6 cm~(-1)is achieved with a fixed injected current of 3.5 A at room temperature.Single-mode emission can be observed in the entire process.The maximum single-mode output power of the external cavity setup is as high as 25 mW and is essential in real applications.     

基于组合模理论设计的激光二极管阵列外腔

针对激光二极管阵列提出了"组合模"概念,计算了组合模的远场分布.每个组合模在远场的空间分布呈双瓣结构.基于激光二极管阵列组合模的远场分布特征,设计了离轴外腔反馈的激光二极管阵列.运用此装置所获得激光二极管阵列的远场分布有了明显变化.与自由运转的激光二极管阵列相比,离轴外腔反馈的激光二极管阵列远场宽度减少了4.3倍.在抽运电流为16 A时,测得输出激光的功率1.82 W,这相当于相同电流下自由运转激光器输出功率的79%.组合模理论不仅可以用来指导设计一维离轴外腔反馈激光二极管阵列,而且也可以用于设计二维离轴外腔反馈激光二极管阵列.二维离轴外腔反馈激光二极管阵列可以产生高功率,高光束质量输出的激光.     

Vacuum-stimulated raman scattering based on adiabatic passage in a high-finesse optical cavity

We report on the first observation of stimulated Raman scattering from a Lambda-type three-level atom, where the stimulation is realized by the vacuum field of a high-finesse optical cavity. The scheme produces one intracavity photon by means of an adiabatic passage technique based on a counterintuitive interaction sequence between pump laser and cavity field. This photon leaves the cavity through the less-reflecting mirror. The emission rate shows a characteristic dependence on the cavity and pump detuning, and the observed spectra have a subnatural linewidth. The results are in excellent agreement with numerical simulations.     

Multiple beam interference in a quadrupolar glass fiber

Motivated by the recent observation of periodic filter characteristics of an oval-shaped microcavity, we study the possible interference of multiple beams in the far field of a laser-illuminated quadrupolar glass fiber. From numerical ray-tracing simulations we obtain the interference-relevant length-difference spectrum and compare it with data extracted from the experimental filter results. Our analysis reveals that different polygonal cavity modes that are refractively output coupled in the high-curvature region of the fiber contribute to the observed far-field interference.     

Surface-structure-assisted chaotic mode lasing in vertical cavity surface emitting lasers

We demonstrate chaotic mode lasing in vertical cavity surface emitting lasers at room temperature, with an open cavity confined laterally by the native oxide layer. Instead of introducing any defect mode, we show that suppression of lower-order cavity modes can be achieved by destroying vertical reflectors with a surface microstructure. Lasing on chaotic modes is observed directly through collecting near-field radiation patterns. Various vertical emission transverse modes are identified by the spectrum in experiments as well as numerical simulations in real and phase spaces.     

Ring and axis mode lasing in quasi-stadium laser diodes with concentric end mirrors

We fabricated quasi-stadium laser diodes whose resonators consist of two concentric curved end mirrors and two straight sidewall mirrors. We observed two lasing modes that correspond to different beam propagations along the cavity axis and along a ring trajectory, and different far-field patterns with wide angular separation. The modes can be selected by control of an electrode pattern. We also show that the far-field patterns numerically obtained by the extended Fox-Li mode calculation method are in good agreement with the experimental results.     

V-shaped metal–dielectric multilayers for far-field subdiffraction imaging

We propose a kind of v-shaped planar silver and dielectric multilayers for far-field subdiffraction imaging. Finite difference time domain simulations reveal that two linear sources with a separation far below the diffraction limit can be magnified by the systems to the extent that conventional far-field optical microscopy can be further manipulated. PACS  78.67.Pt; 07.60.Pb; 42.79.-e; 78.20.-e     

Observation of the wave function of a quantum billiard from the transverse patterns of vertical cavity surface emitting lasers

We demonstrate experimentally that the near-field and far-field transverse patterns of a large aperture vertical cavity surface emitting laser (VCSEL) can be successfully interpreted as a two-dimensional (2D) billiard system. It is found that the near-field and far-field transverse patterns of a large aperture VCSEL evidently represent the coordinate-space and momentum-space wave functions of a 2D quantum billiard, respectively. The result of this paper suggests that large aperture VCSELs are potentially appropriate physical systems for the wave-function study in quantum problems.