Very small oxide-confined vertical microcavity lasers withhigh-contrast AlGaAs-AlxOy mirrors

We report the photo-pumped lasing action from a very small oxide-confined 870-nm vertical microcavity lasers with high-contrast AlGaAs-Al_xO_y mirrors. The effective cavity length is as small as 0.37 μm, and the oxide aperture size is 0.73 μm, estimated from the blue-shift of lasing mode due to the lateral confinement. The observed blue-shift of the lasing mode is 13.4 nm, the largest one ever reported for vertical cavity lasers. The optical losses seem to be size-independent for these small microcavity lasers. Our results indicate the possibility of the ultimate microcavity of order of λ³     

An optical-fiber-based probe for photonic crystal microcavities

We review a novel method for characterizing both the spectral and spatial properties of resonant cavities within two- dimensional photonic crystals (PCs). An optical fiber taper serves as an external waveguide probe whose micron-scale field is used to source and couple light from the cavity modes, which appear as resonant features in the taper's wavelength-dependent transmission spectrum when it is placed within the cavity's near field. Studying the linewidth and depth of these resonances as a function of the taper's position with respect to the resonator produces quantitative measurements of the quality factor (Q) and modal volume (V/sub eff/) of the resonant cavity modes. Polarization information about the cavity modes can be obtained by studying their depths of coupling when the cavity is probed along different axes by the taper. This fiber-based technique has been used to measure Q/spl sim/40,000 and V/sub eff//spl sim/0.9 cubic wavelengths in a graded square lattice PC microcavity fabricated in silicon. The speed and versatility of this fiber-based probe is highlighted, and a discussion of its applicability to other wavelength-scale resonant elements is given.     

高品质因子氧化硅微腔的制备和光频梳产生(特邀)

基于超高品质因子（Q值）和非线性光学微腔产生的光学频率梳（微腔光频梳）在大容量光通信、光学数据中心、光子神经形态运算以及大规模并行激光雷达等方面有着重要的应用。回音壁模式（WGM）微腔是研究微腔光频梳技术的一个重要平台,具有创纪录的超高Q值和超高精细度（Finesse）,能够实现超窄线宽激光、窄线宽光学频率梳,合成超低噪声的光子微波;同时也是研究腔内孤子动力学的重要平台,对掌握孤子态的光学频率梳特性起到了重要的支撑作用。利用二氧化碳（CO₂）激光器熔融氧化硅（SiO₂）石英棒制备了高Q值的WGM微腔。其自由光谱范围（FSR）在10 GHz以上,Q值达到了108。对腔的谐振和耦合理想特性进行了表征,并在开放环境下观察到微腔受潮引起的Q值退化现象,通过二次退火实现了Q值的回升。在SiO₂微腔中验证了基于非线性克尔（Kerr）效应的光学频率梳产生,其主要状态为调整不稳定性主导的低相干频率梳。同时,实验中也观察到了对应于全相干耗散孤子态频率梳的“阶跃”信号,表明目前制备的SiO₂微腔具备实现低噪声孤子光频梳的能力,并具有微腔光频梳的应用潜力。     

Design and Optimization of TE011 Resonant Modes in Metallic-Dielectric Cavities

In this work, we present an innovative approach for designing small-scale microcavity resonators. By introducing a gold cladding around the structure, we may significantly reduce the mode volume and simultaneously increase the cavity's quality Q-factor. By making use of the TE₀₁₁ mode, as opposed to the more traditional HE₁₁₁ mode, we may further reduce the mode volume while taking advantage of decreased loss into the metal layer due to the optimal polarization choice. We demonstrate a means to design and optimize the cavity geometry to obtain desired spectral characteristics through the use of particle swarm optimization, and we present a cavity operating at 1.5 mum with a Q value exceeding 300 000 and a modal volume of less than 0.9(lambda/n)³.     

Resonance wavelength‐tunable microcavities

We describe a microcavity device structure which allows external control of the resonance wavelength of the cavity via alignment of a liquid crystal layer within the cavity. This also allows the study of the spectral and spatial distribution of emission from a single emitter within the microcavity. We have been able to shift the resonance modes of the microcavity by up to 56 nm. The tunability of the microcavity has been used to further investigate the coupling between an emitter and a microcavity. The potential technical applications for this type of device are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Cylindrical TE/sub 011/ /TM/sub 111/ Mode Control by Cavity Shaping

An appropriate modification of the shape of a cylindrical filter cavity has been used to separate the degenerate TM/sub 111/ (doublet) modes while at the same time providing a slight increase in the already high unloaded Q of the desired TE/sub 011/ mode. Experimental results of mode frequencies and unloaded Q's are tabulated for a family of shaped cavities. Two low-loss filters utilizing these cavities are discussed. The general correspondence between modes of spherical, cylindrical and rectangular cavities and waveguides is described in order to place the performance of intermediate shapes in perspective.     

Analytic theory of a tapered gyrotron resonator

An analytic theory has been derived for determining the eigenfrequencies, RF-field distribution and Q of the TE_mpq modes of a gyrotron resonator consisting of a circular cylinder joined to a slowly tapered section. Explicit results are obtained for a linear taper. The cavity modes are found to have an RF-field distribution which is useful for prebunching the electron beam and enhancing efficiency. For high Q cavities, the cavity Q depends on axial mode number q as q^?2, which is important for mode discrimination. Proper selection of taper length is found to reduce the Q of high q modes, also aiding in mode discrimination. The present approach may be applied to other forms of weakly irregular cavities, such as cavities with nonlinear tapers.     

Optical modes in 2-D imperfect square and triangular microcavities

Transformation of the whispering-gallery (WG)-modes in imperfect two-dimensional square and triangular microcavities with various degrees of deformation is studied by means of the Muller boundary integral equation technique. Continuous transformation of a circular microcavity, which supports double-degenerate WG-modes, toward a square or a triangle removes the degeneracy of certain WG-modes. The spectrum of the modes that split depends on the symmetry of the emerging microcavity: WG/sub 2m,n/-modes in case of a C/sub 4v/ symmetry (square) or WG/sub 3m,n/-modes in the case of C/sub 3v/ symmetry (triangle). In both cases, the modes with the highest Q-factors are nondegenerate modes with antisymmetrical field patterns. We estimate mode frequencies, quality factors and field distributions of practically achievable rather than "ideal" square and triangular microcavities, and compare the effect of various types of fabrication imperfections (corner sharpness, sidewall curvature and surface roughness) on their characteristics. Accurate study of the modal spectra enables us to confirm and explain previous observations, such as: 1) co-existence of the WG-like and volume modes in square microcavities; 2) the separation of the high-Q WG-like modes being twice that determined by the cavity length; and 3) much lower Q-factors of realistic concave-wall triangular microcavities than those of their ideal counterparts.     

A Novel 3-D Microcavity Based on Bragg Fiber Dual-Tapers

In this paper, a novel 3-D microcavity based on Bragg fiber dual-tapers is proposed. The principle and characteristics of the Bragg fiber dual-taper are analyzed firstly, showing that the dual-taper can function as a fiber mirror. Its reflection and transmission can be adjusted by the design of taper structure parameters. Then, the structure of a 3-D microcavity composed by two Bragg fiber dual-tapers is investigated by the finite-difference time domain method. The relation between the cavity-mode wavelengths and the cavity lengths shows that it can be looked as a Fabry–PÉrot cavity, using the Bragg fiber dual-tapers as the mirrors. By proper design, a cavity-mode Q factor up to $4.0093times 10^{6}$ can be realized in this cavity. Its characteristics as narrowband filters are investigated, showing that its transmission spectrum has the shape of Lorenz curve and a finesse up to $10^{5}$ can be realized if cavity mode with a high Q factor is used. The analysis shows that high-quality 3-D light confinement can be realized in the proposed Bragg fiber dual-taper microcavity, which has great potential in high-efficiency light-emitting devices and small fiber components.      

光泵浦Si衬底GaN基回音壁模式微盘谐振腔激光器

氮化镓基微盘结构光学谐振腔具有波长选择范围宽、模式体积小和激射阈值低等特点,其在腔量子电动力学、低阈值激光器、生物传感器等方面具有重要的研究价值.通过优化制备微盘的干法刻蚀工艺及选择性湿法腐蚀技术,制备出侧壁陡峭且光滑的高Q值Si衬底GaN基回音壁模式微盘谐振腔,该微盘谐振腔的制备工艺简单、表面损伤小.在室温、266 nm短波长激光泵浦条件下,微盘谐振腔激光器实现了激射,阈值为2.85 MW/cm2,Q值达到2161.     

Self-consistent calculation of lasing modes in a planar microcavity

The self-consistent calculation of lasing modes in a microcavity with infinite plane mirrors is presented. The semiclassical theory is used, with rigorous boundary conditions included for Maxwell's equations to describe both the emitter distribution and the cavity reflectors. The concept of gain-guided versus index-guided modes in such structures can be removed within the semiclassical model, as rigorous boundary conditions for both the radiation source and passive cavity can be handled exactly. We present calculated curves showing the angular dependence of various lasing modes on mirror reflectivity and the threshold gain susceptibility dependence on mirror reflectivity and active diameter. The linewidth dependence on the transverse lasing mode is also considered. Limitations of the semiclassical approach as compared to a fully quantum mechanical approach is emphasized     

Steady-state and transient characteristics of microcavitysurface-emitting lasers with compressively strained quantum-well activeregions

In conventional semiconductor lasers, the dimensions of the optical cavity greatly exceed the photon wavelength, and the photon density of states forms a continuum since it is essentially that of a bulk system. On the other hand, in an ideal laser, one would like to have a single optical mode coincident with the maximum in the gain spectrum of the active medium. We show that substantial density-of-states quantization and enhancement of the fraction of photons spontaneously emitted into the lasing mode can be obtained by reducing the lateral width of the surface-emitting laser. For emission at λ=0.954 μm, the threshold current density can be drastically reduced by increasing the coupling factor to a few percent. For a cavity structure width of 0.3 μm, the threshold current density is 50 A/cm², compared with 250 A/cm² for the 0.6-μm cavity. At lower still lateral widths, the cavity loses its vertical character, and confinement of the lateral optical mode rapidly deteriorates. The large-signal response of microcavity lasers is slightly improved primarily due to elimination of mode competition in intrinsically single-mode microcavities, with relaxation times close to 1 ns. The enhancement of the spontaneous emission coupling factor results in an increase of the relaxation oscillation frequency and improvement in the standard small-signal response of microcavity lasers. For J=10J_th, the -3 dB modulation frequency exceeds 40 GHz. Since low threshold current densities may be achieved in microcavity lasers, the gains in small-signal performance are primarily extrinsic, i.e., higher modulation bandwidths ace accessible for the same injection     

Mode-coupling Characteristics and efficiency of quantum-dot electrically injected photonic Crystal waveguide-coupled light-emitting diodes

We have studied the transverse coupling of optical modes between a quantum-dot photonic crystal microcavity light-emitting diode and a photonic crystal missing-defect waveguide. From the emission spectra, it is evident that higher order anticrossings participate in the output coupling process. A 3% coupling efficiency between cavity and waveguide modes is estimated.     

Impact of planar microcavity effects on light extraction-Part I:basic concepts and analytical trends

We address the long-standing issue of extracting light as efficiently as possible from a high-index material, n⩾2, where as little as 2%-10% of light not suffering total internal reflection is extracted at standard plane faces due to the small critical angle ~1/n. Using a planar microcavity to redirect spontaneous emission toward the surface, constructive interferences can bring 15%-50% of the light out, enhancing brightness and efficiency. In this first of two papers, an approximate approach is used showing the importance of small cavity order m_c and of the m_c/n² ratio. We define a condition for microcavity regime as m_c<2n² . It is shown that most of light extraction is usually attained for moderate mirror reflectivities ~1-m_c/n² typically below 90%, and without strong directionality. Balance between emission directionality, radiance (brightness), and spectral narrowing is discussed. We define a brightness enhancement factor B given by Bm _cΔΩ=4π where ΔΩ is the largest internal solid angle of either the cavity mode or that deduced from the material emission linewidth. Design rules are applied to distributed dielectric mirrors yielding an optimal number of periods. The underlying physical competition between emission into guided modes, Fabry-Perot modes and the so-called “leaky modes” is analyzed     

Bloch-wave engineering for high-Q, small-V microcavities

The overall decay rate of the mode in an optical microcavity formed by a defect surrounded by two Bragg mirrors in a monomode waveguide is driven by two mechanisms, the desired coupling to a guided mode and the detrimental coupling to radiation modes. We propose two approaches fully compatible with planar fabrication, which allow to increase the cavity Q's by several orders of magnitude while keeping constant the mode volume V of the cavity. The first approach consists of engineering the mirror to taper the guided mode into the mirror Bloch mode, thus decreasing losses. The second approach is less intuitive and relies on a recycling mechanism of the radiation losses. The study is supported by computational results obtained for two-dimensional silicon-on-insulator geometries, but the results apply as well to other related geometries like three-dimensional photonic-wire cavities.     

Fabrication of Microcavity Light-Emitting Diodes Using Highly Reflective AlN–GaN and Ta2O 5–SiO2 Distributed Bragg Mirrors

We report the fabrication of microcavity light-emitting diodes (MCLEDs) with high reflectivity and crack-free AlN-GaN distributed Bragg reflector (DBR). The 5lambda microcavity structure consists of an n-type GaN, ten pairs InGaN-GaN multiple quantum wells and p-type GaN sandwiched between the hybrid cavity mode of an AlN-GaN and a Ta₂O₅-SiO₂ DBR. The AlN-GaN DBR has 29 periods with insertion of six AlN-GaN superlattice layers showing a crack-free surface morphology and a high peak reflectivity of 99.4% with a stopband of 21 nm. The output power of MCLED is about 11 W at an injection current of 7 mA. The electroluminescence has a polarization property with a degree of polarization of about 51%.     

A new type of waveguide ring cavity for resonator and filterapplications

A new type of rectangular waveguide ring cavity has been developed for applications to resonators, filters, and multiplexers. The circuits have advantages of high Q and high power handling capability. H-plane and E-plane waveguide ring cavities have been investigated thoroughly in single-mode and dual-mode operations. For single-mode operation, regular resonant modes, split resonant modes, and forced resonant modes were explained by resonant mode charts of E-field points. Mechanically tuned and electronically tuned resonators built by adjusting the resonant modes between regular resonant modes and forced resonant modes have been demonstrated. For dual-mode operation, a dual-mode filter using a single H-plane ring cavity has been built with a bandwidth of 0.77%, a stopband attenuation of more than 40 dB, and a sharp gain slope transition. Another dual-mode filter which was formed by cascading two E-plane ring cavities has also been fabricated with a bandwidth of 1.12%, a stopband attenuation of 70 dB, a mode purity of 2 GHz at the center frequency of 26.82 GHz, and a sharp gain slope transition     

Analysis of microcavity VCSEL lasing modes using a full-vectorweighted index method

Presents a semi-analytic full-vector method for calculating the spatial profile, optical confinement factor resonant frequency, absorption loss, and mirror loss of lasing modes in cylindrically symmetric microcavity vertical-cavity surface-emitting lasers (VCSEL's). It can be shown that this method gives the best separable approximation for the electric and magnetic vector potentials. Our technique can model the entire VCSEL structure and can treat complex media. We apply the method to etched-post and oxide-apertured VCSEL's designed for 980-nm emission and find a blueshift in cavity resonance as the cavity radius shrinks. We also find a minimum optical cavity radius below which radially bound lasing modes cannot be supported. This radius depends on the device geometry and lies between 0.5 and 1 μm for the devices studied. Once this model is augmented to include diffraction losses-the dominant loss mechanism for conventional small aperture lasers-it will provide a complete picture of lasing eigenmodes in microcavity VCSEL's     

波导耦合多层结构光学微球腔性能分析

利用时域有限差分(FDTD)法模拟了均匀结构、双层结构和三层结构光学微球腔,得到了各自的能量密度分布,通过对比发现多层结构具有更高的最大能量密度与存储能量和较小的模式体积。波导与多层微球腔之间存在一个最佳间隙,模拟结构的最佳间隙在60～120nm。改变高折射层的厚度和折射率,在特定波长的入射光下可以获得具有较高最大能量密度(大于360)或者较小模式体积的(小于0.03)的微球腔,确定了优化的厚度和折射率。分析高斯光激励的带有导出波导的微球腔,导出波导与微球腔中的光具有相似的激发频谱,表明多层微球腔可以对入射光实现选频并导出。结果显示,多层微球腔具有更好的性能,为光学微球腔后续的结构设计和实际应用提供了一个新的优化思路。     

三维半导体GaAs量子阱微腔中的腔极化激元

半导体微腔中腔模和激子模耦合形成腔极化激元,三维微腔中由于横向限定腔模和激子模形成离散化的本征模式.本文计算了远离截止近似下,三维半导体微腔中空腔腔模的能量与微腔半径的关系;及腔模和激子模耦合后,三维半导体柱型微腔中具有相同角量子数和径向量子数的两个低阶腔模、重空穴激子模、轻空穴激子模耦合形成的腔极化激元能量随微腔半径变化的情况.结果表明随着微腔半径的减小腔模能量蓝移,腔模与相应的重空穴激子模、轻空穴激子模耦合形成的腔极化激元的三支随着微腔半径的减小存在明显的反交叉行为.随着微腔半径的变化,极化激元的三支所体现的模