Tuning of exciton-photon coupling in a planar semiconductor microcavity by applying hydrostatic pressure

By means of hydrostatic pressure tuning, we have observed the strong-coupling exciton-polariton mode in a planar microcavity with an InGaAs/GaAs quantum well embedded in it, over a pressure range from 0.37 to 0.41 GPa. The experimental data can be fitted very well to a corresponding theoretical formula with a unique value of the vacuum Rabi splitting equal to 6.0 meV. A comparison between pressure tuning and other tuning methods is made as regards to what extent the intrinsic features of the exciton and cavity will be influenced during the tuning procedure.

Partially coherent tunneling through a series of barriers: Inelastic scattering versus pure dephasing

Within the Buttiker dephasing model, the backscattering in the dephasing process is eliminated by setting a proper boundary condition. Explicit expression is carried out for the effective total tunneling probability in the presence of multiple pure dephasing scatterers with partial coherence. The derived formula is illustrated analytically by various limiting cases, and numerically for its application in tunneling through multibarrier systems.

Simple method for estimating minimum bend radii of SOI single mode curved rib waveguides

A simple method based on the effective index method was used to estimate the minimum bend radii of curved SOI waveguides. An analytical formula was obtained to estimate the minimum radius of curvature at which the mode becomes cut off due to the side radiative loss.

Multiplicity factor and diffraction geometry factor for single crystal X-ray diffraction analysis and measurement of phase content in cubic GaN/GaAs(001) epilayers

On the basis of integrated intensity of rocking curves, the multiplicity factor and the diffraction geometry factor for single crystal X-ray diffraction (XRD) analysis were proposed and a general formula for calculating the content of mixed phases was obtained. With a multifunction four-circle X-ray double-crystal diffractometer, pole figures of cubic (002), {111} and hexagonal {1010} and reciprocal space mapping were measured to investigate the distributive character of mixed phases and to obtain their multiplicity factors and diffraction geometry factors. The contents of cubic twins and hexagonal inclusions were calculated by the integrated intensities of rocking curves of cubic (002), cubic twin {111}, hexagonal {1010} and {1011}.

Resonant frequencies and quality factors for optical equilateral triangle resonators calculated by FDTD technique and the Pade approximation

The mode wavelength and quality factor (Q-factor) for resonant modes in optical equilateral triangle resonators (ETR's) are calculated by the finite-difference time-domain (FDTD) technique and the Pade approximation, For an ETR with the side length of 3 mu m and the refractive index of 3.2, we get the mode wavelength interval of about 70 nm and the Q-factor of the fundamental mode over 10(3), The results show that the ETR is suitable to realize single-mode operation, and that the radiation loss in the corner regions of ETR is rather low, In addition, the numerical results of the mode wavelength agree very well with our analytical formula.

Optical-phonon modes and Frohlich potential in quantum dots

By extending the microscopic dipole model on optical-phonon modes as applied in quantum wells and quantum wires, to rectangular quantum dots (QD), optical phonon modes and their accompanying Frohlich potentials in QD are calculated and classified. When the bulk phonon dispersion is ignored, the optical phonon modes in QD can be clearly divided into the confined LO- and TO-bulk-like modes and the extended interface-like modes. Among the interface-like modes, a special attention is given to the corner modes, whose anisotropic behavior is depicted in the long wavelength limit. Based on the numerical results, a set of analytical formula are proposed to approximately describe the bulk-like modes, for which both the optical displacements and Frohlich potentials vanish at the interfaces. (C) 2000 Elsevier Science Ltd. All rights reserved.

Electron transport through a double-quantum-dot structure with intradot and interdot Coulomb interactions

Electron transport through a double-quantum-dot structure with intradot and interdot Coulomb interactions is studied by a Green's function (GF) approach. The conductance is calculated by a Landauer-Buttiker formula for the interacting systems derived using the nonequilibrium Keldysh formalism and the GF's are solved by the equation-of-motion method. It is shown that the interdot-coupling dependence of the conductance peak splitting matches the recent experimental observations. Also, the breaking of the electron-hole symmetry is numerically demonstrated by the presence of the interdot repulsion. [S0163-1829(99)01640-9].

Electronic structure and optical gain saturation of InAs1-xNx/GaAs quantum dots

The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143025]

Electronic structures of wurtzite ZnO and ZnO/MgZnO quantum well

The band structures of wurtzite ZnO are calculated using the empirical pseudopotential method (EPM). The 8 parameters of the Zn and O atom pesudopotential form factors with Schluter's formula are obtained. The effective mass parameters are extracted by using k.p Hamiltonian to fit the EPM results. The calculated band edge energies (E-g, E-A, E-B, and E-C) at Gamma point are in good agreement with experimental results. The ordering of ZnO at the top of valence band is found to be A(Gamma(7))-B(Gamma(9))-C(Gamma(7)) due to a negative spin-orbit (SO) splitting. Based on the band parameters obtained, the valence hole subbands of wurzite ZnO/MgxZn1-xO tensile-strained quantum wells (QWs) with different well widths and Mg compositions are calculated using 6-band k.p method. (c) 2005 Elsevier B.V. All rights reserved.

Structural optimizations of SOI-based single-mode rib waveguide bends

Effects of structure parameters on bend loss of rib silicon-on-insulator (Sol) bend waveguides have been analyzed by means of effective index method (EIM) and 2D bend loss formula. The simulation results indicate that the bend loss decreases with the increase of bend radius and waveguide width, as well as with the decrease of the step factor of the rib waveguide. Moreover, the optional structure parameters have been found when bend waveguides are single-mode.

When is `partial' adequate? A logic-based proof technique using partial specifications

A technique is presented for ascertaining when a (finite-state) partial process specification is adequate, in the sense of being specified enough, for contexts in which it is to be used. The method relies on the automatic generation of a modal formula from the partial specification; if the remainder of the network satisfies this formula, then any process that meets the specification is guaranteed to ensure correct behavior of the overall system. Using the results, the authors develop compositional proof rules for establishing the correctness of networks of parallel processes and illustrate their use with several examples

mod 2n加运算与F2上异或运算差值的概率分布和递推公式

提出了一种计算单mod 2~n加运算与F_2上的异或运算的“异或差值”概率分布的有效算法，该算法的计算复杂度为O（（n-1）／2），与Maximov的结果相比计算复杂度更低．对于多mod 2~n加运算的情形，给出了多mod 2~n加运算与F_2上的异或（XOR）运算的“异或差值”的递推计算公式．

Unified theory for Goos-Hanchen and imbert-fedorov effects

A unified theory is advanced to describe both the lateral Goos-Hanchen (GH) effect and the transverse Imbert-Fedorov (IF) effect, through representing the vector angular spectrum of a three-dimensional light beam in terms of a two-form angular spectrum consisting of its two orthogonal polarized components. From this theory, the quantization characteristics of the GH and IF displacements are obtained, and the Artmann formula for the GH displacement is derived. It is found that the eigenstates of the GH displacement are the two orthogonal linear polarizations in this two-form representation, and the eigenstates of the IF displacement are the two orthogonal circular polarizations. The theoretical predictions are found to be in agreement with recent experimental results.

Philip公式确定吸渗率时间尺度研究

选用直径5 cm和10 cm的盘式吸渗仪,对杨凌土(粘土)和神木砂黄土(砂壤土)两种质地的土壤在1 cm、3 cm6、cm9、cm和12 cm水头5种负压下进行了室内盘式吸渗仪三维吸渗实验,选取Vandervaere公式作为参考模型,对Philip公式确定吸渗率的时间尺度选取进行了分析。结果表明,对两种质地的土壤,在相同盘径下,随着负压的降低,吸渗率随之减小;在相同负压下,盘径越小,吸渗率越大;质地较砂的砂黄土吸渗率明显大于质地较粘的土的吸渗率。从相对误差来看,两种质地土壤吸渗率均被高估;在同一盘径下,随着负压的减小,误差值逐渐降低;即在选取的时间范围内,负压越低,计算吸渗率的准确性越高。对土而言,5 cm盘径下-12 cm水头1、0 cm盘径下-9 cm水头和-12 cm水头时确定吸渗率的适宜时间分别为30~40 s和40~50 s;其余确定吸渗率的适宜时间均应小于30 s;对砂黄土而言,10 cm盘径下-9 cm水头和-12 cm水头时确定吸渗率的适宜时间分别为30~40 s和40~50 s,其余确定吸渗率的适宜时间也均应小于30 s。对于质地较砂的土壤推荐使用大盘径进行盘式吸渗仪实验。