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1.
采用麦克斯韦方程和速率方程相结合的模型和时域有限差分法,利用引入的有效增益分布因子概念研究了光子晶体中本征模的阈值特性。增益介质的大小以及在光子晶体中的位置直接影响光子晶体带边激光器的输出特性;有效增益分布因子描述了光子晶体中增益介质的空间分布特性。结果显示,带边本征模的激射阈值依赖于有效增益分布因子。不同的本征模具有不同的有效增益分布因子,那些有效增益分布因子较大的模式具有较低的阈值。通过调整增益介质的位置和长度,可以提高有效增益分布因子的值,从而降低激光器的阈值,这对于实现激光器的低阈值运行有指导作用。 相似文献
2.
The band structures of rectangular GaN/AlGaN quantum wires are modeled by using a parabolic effective-mass theory.The absorption coefficients are calculated in a contact-density matrix approach based on the band structure.The results obtained indicate that the peak absorption coefficients augment with the increase of the injected carrier density,and the optical gain caused by interband transition is polarization anisotropic.For the photon energy near 1.55 eV,we can obtain relatively large peak gain.The calculations support the previous results published in the recent literature. 相似文献
3.
该文的工作是设计和制作了一种具有陷波电路结构的P波段低温低噪声放大器。在低温75K环境下,工作频段为250-350MHz的范围内,该低温低噪声放大器具有优异的性能,噪声系数小于0.4dB,增益为14.4dB,增益平坦度小于0.05dB,输入反射损耗S11<-20dB,输出反射损耗S22<-20dB。同时在工作频段外的高温超导滤波器寄生通带内,该低温低噪声放大器成功实现了传输陷波响应,加强了系统对前端高温超导滤波器产生的寄生通带的衰减和抑制。 相似文献
4.
讨论了不同In组分对InGaAsSb/GaSb量子阱能带结构,即带隙及带边不连续性(带阶)的影响。给出了较为精准的InGaAsSb禁带宽度与In组分的关系。分析了In组分对InGaAsSb/GaSb导带、价带带阶的作用。研究表明,随In组分的增加,InGaAsSb禁带宽度减小,应力加大,能带漂移增大,InGaAsSb/GaSb导带、价带的带阶减小。同时,利用上述研究结果合理地解释了InGaAsSb/GaSb自发发射谱的增益、发射峰位及半峰宽与In组分关系。研究In组分对InGaAsSb/GaSb量子阱能带结构及自发发射谱的影响,可以定性地解释已有的实验报道。 相似文献
5.
在PTDS(Photonic Transmission Design Suite)仿真平台上,用3个泵浦源的RFA实现了S波段的增益平坦,同时对泵浦光与信号光,信号光与信号光,泵浦光与泵浦光之间的相互作用以及RFA的噪声特性进行了研究. 相似文献
6.
Analysis is performed for valence band structures and some characteristics of InGaAs/InGaAsP strain-compensated quantum well lasers lattice-matched to InP substrate. The computed results show that band offsets are functions of strain compensation instead of constants; strain compensation changes the band structures and the density of states, and hence affects the optical gain and the threshold current density. Under the condition of zero net strain, the values of the well width, cavity length and relative threshold carrier density and threshold current density are determined for realization of 1.55 m wavelength emission. 相似文献
7.
The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities. 相似文献
8.
1 Introduction Today,withthequickdevelopmentofthehighdensewavelengthdivisionmultiplexing,thelinkcapacitywillbegreatlyenhanced.Alternatively,theenhancementofthelinkcapacitydependsontherelativelyhighwavelengthresolutionofthewavelengthfiltersintherecei… 相似文献
9.
A simple yet generalized theory is developed to study inter band tunneling property of narrow band gap III–V compound semiconductors. The band structures of these low band gap semiconductors with sufficiently separated split-off valance band are usually described by the three energy band model of Kane, so this has been adopted here for the analysis of interband tunneling property in the case of InAs, InSb, and In 1-xGa xAs yP 1-y lattice matched to InP as representative direct band gap semiconductors having varied split-off valence band compared to their bulk state band gap energy. It has been found that the magnitude of tunneling rate from heavy hole decreases with increasing band nonparabolicity and the impact is more significant at high electric field in the three-band model of Kane than those with simple parabolic energy band approximations reflecting the direct influence of energy band parameters on inter band tunneling transitions. With proper consideration of band nonparabolicity, the results of the analysis of tunneling rate of these narrow gap materials show significant deviations from the results when simple parabolic band approximation is considered. The exact physical basis of the sources of deviation in the nonparabolic case from the corresponding parabolic band approximations is discussed in association to band coupling effect, transverse energy dependence, and the interplay between them. Moreover, under certain limiting conditions, our results reduce to the well-known results of parabolic band approximation and thus providing an indirect test to the accuracy of our generalized formulations. 相似文献
10.
Superconductivity has been observed in bilayer graphene [1, 2]. The main factor that determines the mechanism of the formation of this superconductivity is the “magic angle” of twist of two graphene layers, at which the electronic band structure becomes nearly flat. The specific role played by twist and by the band flattening has been earlier suggested for explanations of the signatures of room-temperature superconductivity observed in the highly oriented pyrolytic graphite (HOPG), when the quasi two-dimensional interfaces between the twisted domains are present. The interface contains the periodic array of misfit dislocations (analogs of the boundaries of the unit cell of the Moiré superlattice in bilayer graphene), which provide the possible source of the flat band. This demonstrates that it is high time for combination of the theoretical and experimental efforts in order to reach the reproducible room-temperature superconductivity in graphite or in similar real or artificial materials. 相似文献
11.
The g-factors of the positive parity rotational states up to spin I = 8^+ for the ground state band in even-even nuclei S2Sr have been measured by a transient-magnetic-field ion implantation perturbed angular distribution method. The experimentally measured 9-factors increase with the increasing spin along the band and show that the g9/2 proton aligns only and the alignment starts from I =6^+. The measured g-factors also indicate that the nuclei ^82Sr gain their spins by the quasi-proton alignment at higher spin. 相似文献
12.
It is shown that certain ensembles of random matrices with entries that vanish outside a band around the diagonal satisfy
a localization condition on the resolvent which guarantees that eigenvectors have strong overlap with a vanishing fraction
of standard basis vectors, provided the band width W raised to a power μ remains smaller than the matrix size N. For a Gaussian band ensemble, with matrix elements given by i.i.d. centered Gaussians within a band of width W, the estimate μ ≤ 8 holds. 相似文献
13.
A new type of ultra-wide band(UWB) conical antennas ridged by a novel taper finline radiator(TFR) used as radiation and receiving of the short pulse are developed. In which, a new UWB feed structure of a coplanar waveguide to finline and a TFR ridge are used initially. The experiment results show the characteristics of high fidelity, high efficiency, and high gain compared with some common broad-band antennas such as the biconical antennas, V-conical antennas, logarithm periodic antennas, and the other TEM horns. 相似文献
14.
In the general case of the confined one-dimensional photonic crystal (PC), the properties of transparency windows near the band gap, in which the field amplitude significantly increases, are studied using the perturbation theory. Expressions for the dependences of the maximum gain of the field amplitude, positions and widths of transparency windows on crystal thickness H and window number n are obtained; in this case, the knowledge of particular types of fields are not required. Expressions for the field in the crystal and the intensities of reflected and transmitted light, which are defined by the fields at the quasimomentum q0 corresponding to the band edge, are obtained. 相似文献
15.
The flat bands in a square kagome lattice containing square and triangle plaquettes, are respectively investigated, and the origin of the doubly degenerated completely flat bands and the corresponding compact localized states are elucidated. It is found that the introduction of external magnetic flux enriches the modulation parameters, making the system present many interesting results. In the case that the magnetic flux penetrates through each square plaquette, the tunable completely flat band has one more tunable parameter. And when the external magnetic flux penetrates through each triangle plaquette, excepting a completely flat band, the band dispersions of the system present the topological nearly flat band, which is very useful to realize the interesting fractional quantum Hall physics. The average density of states is also calculated to corroborate the completely FB generated by the highly localized eigenstates. Furthermore, the implementation of the square kagome lattice system based on the current photonic waveguide network technology is demonstrated. The scheme opens up a way to generate the tunable completely flat band and topological nearly flat band in square kagome lattice under multi-parameter variable conditions. 相似文献
16.
High spin states of 118Xe have been investigated by means of γ ray spectroscopy using the 92Mo( 29Si,2pn) at a bombarding energy of 110 MeV. Several new side bands as well as the yrast band were established. A band crossing between the ground state and super bands was observed at ?ω c = 0.39 MeV. A negative parity band with two quasi particle excitation, and a quasi γ band were also identified. 相似文献
17.
A self-consistent calculation of the band structure of copper has been performed using a basis of gaussian orbitals and a local exchange-correlation potential. Results are also presented for the optical conductivity and the Compton profile. 相似文献
18.
Band structures of 76Se and 78Se have been studied with the 74,76Ge(, 2nγ) 76,78Se reactions by using a variety of in-beam γ-techniques : γ-ray singles spectra, γ-ray excitation functions, γ-γ- t coincidences, γ-ray angular distributions and γ-ray linear polarizations. Spins and parities have been assigned uniquely for many new levels in 76Se and 78Se and four bands have been identified in both nuclei: (i) the ground-state band, (ii) a positive-parity ΔJ = 1 band built on the second 2+ state (γ-vibrational band), (iii) a negative-parity Δ J = 2 band built on the 3− state (octupole band) and (iv) a ΔJ = 2 band built on the high-lying J = 4 state. In addition, the second 8 + and 10+ states, which are possibly the lowest members of a band, have been found in both nuclei. Systematics of the band structures obtained are discussed. Level energies of the band members and B(E2) ratios for some of the inter-band transitions between γ- and ground-state bands have been calculated with the proton-neutron interacting boson model IBM-2 and a reasonable agreement with the present data has been obtained. 相似文献
19.
The band structure of a two-dimensional superconducting photonic crystal is investigated. This crystal is considered a periodic system of nonoverlapping cylinders that have a circular cross section and are infinite in length. The results are obtained using the method of plane wave expansion of eigenfunctions. The photonic band structure is analyzed for two temperatures, namely, in the vicinity of the superconducting transition point and far from it. The two-dimensional superconducting photonic crystal is found to have complete and incomplete band gaps at low temperatures. As the temperature increases, these band gaps shift toward the short-wavelength range. 相似文献
20.
The energy band structure of wurtzite-structure semiconductive InN is predicted using empirical nearest-neighbor tight-binding theory. The tight-binding parameters are extrapolated from those of zincblende InP, InAs, and InSb by using empirical rules for the dependences of the parameters on bond length and on row of the Periodic Table. The predicted band gap is direct and agrees well with the data for this potential orange light-emitter. It is suggested that zincblende InN, if it can be grown, also will have a band-gap near 2 eV. 相似文献
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