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First-principles study of electronic and optical properties in wurtzite Zn_(1-x)Cu_xO

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Chinese Physics B 2010年第5期19卷 427-433页

作者：赵龙芦鹏飞俞重远刘玉敏王东林叶寒 key laboratory of information photonics and optical communications(Beijing University of Posts and Telecommunications) Ministry of Education

We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1-xCuxO. The simulations are based upon the Perdew-Burke-Ernzerhof form of generalised gradient approximation within the density functional theory. Calculations are carried out in different concentrations. With increasing Cu concentration, the band gap of Znl-xCuxO decreases due to the shift of valence band. The imaginary part of the dielectric function indicates that the optical transition between O2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases. Besides, it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge. Meanwhile, the optical constants of pure ZnO and Zn0.75Cu0.250, such as loss function, refractive index and reflectivity, are discussed.

关键词： density functional theory Cu-doped ZnO electronic structure optical properties

Numerical investigation of slow solitons in Bragg gratings with a hyperbolic tangent apodization

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Chinese Physics B 2011年第3期20卷 268-273页

作者：王葵如程洁琳桑新柱陈功 key laboratory of information photonics and optical communications of ministry of education Beijing University of Posts and Telecommunications

This paper numerically and analytically investigates the formation and propagation motion of optical soliton in the Bragg grating. We choose the fibre Bragg grating with hyperbolic tangent apodization in the middle section in order to obtain slower solitons. optical fibre soliton but not Bragg grating soliton is used as input pulse in the discussion, which is much more approximate to the light source for the practical purpose. We discuss in detail the effects of the soliton＇s velocity with some parameters in the process of transmission. The results show that by choosing special parameters, one can make the soliton slow-down with a little distortion and energy decay and obtain tunable time-delay on a small scale.

关键词： fibre grating slow light soliton hyperbolic tangent apodization

The electronic and magnetic properties of (Mn,C)-codoped ZnO diluted magnetic semiconductor

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Chinese Physics B 2012年第9期21卷 430-435页

作者：赵龙芦鹏飞俞重远马世甲丁路刘建涛 key laboratory of information photonics and optical communications of ministry of education Beijing University of Posts and Telecommunications

The electronic and magnetic properties of （Mn,C）-codoped ZnO are studied in the Perdew Burke-Ernzerhof form of generalized gradient approximation of the density functional theory. By investigating five geometrical configurations, we find that Mn doped ZnO exhibits anti-ferromagnetic or spin-glass behaviour, and there are no carriers to mediate the long range ferromagnetic （FM） interaction without acceptor co-doping. We observe that the FM interaction for （Mn,C）-codoped ZnO is due to the hybridization between C 2p and Mn 3d states, which is strong enough to lead to hole-mediated ferromagnetism at room temperature. Meanwhile, we demonstrate that ZnO co-doped with Mn and C has a stable FM ground state and show that the （Mn,C）-codoped ZnO is FM semiconductor with super-high Curie temperature （Tc =5475 K）. These results are conducive to the design of dilute magnetic semiconductors with codopants for spintronics applications.

关键词： density functional theory electronic structure magnetism Curie temperature

The influence of strain-reducing layer on strain distribution and ground state energy levels of GaN/AlN quantum dot

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Chinese Physics B 2009年第10期18卷 4136-4142页

作者：刘玉敏俞重远任晓敏徐子欢 key laboratory of information photonics and optical communications (Beijing University of Posts and Telecommunications) Ministry of Education

This article deals with the strain distributions around GaN/AlN quantum dots by using the finite element method. Special attention is paid to the influence of Al0.2Ga0.8N strain-reducing layer on strain distribution and electronic structure. The numerical results show that the horizontal and the vertical strain components are reinforced in the GaN quantum dot due to the presence of the strain-reducing layer, but the hydrostatic strain in the quantum dot is not influenced. According to the deformation potential theory, we study the band edge modifications and the piezoelectric effects. The result demonstrates that with the increase of the strain reducing layer, the transition energy between the ground state electron and the heavy hole increases. This result is consistent with the emission wavelength blue shift phenomenon observed in the experiment and confirms that the wavelength shifts toward the short wavelength range is realizable by adjusting the structure-dependent parameters of GaN/AlN quantum dot.

关键词： quantum dot strain distribution electronic structure

Electronic and optical properties of GaN/AlN quantum dots with adjacent threading dislocations

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Chinese Physics B 2010年第4期19卷 375-380页

作者：叶寒芦鹏飞俞重远姚文杰陈智辉贾博雍刘玉敏 key laboratory of information photonics and optical communications Ministry of EducationBeijing University of Posts and Telecommunications

We present a theory to simulate a coherent GaN QD with an adjacent pure edge threading dislocation by using a finite element method. The piezoelectric effects and the strain modified band edges are investigated in the framework of multi-band κ · p theory to calculate the electron and the heavy hole energy levels. The linear optical absorption coefficients corresponding to the interband ground state transition are obtained via the density matrix approach and perturbation expansion method. The results indicate that the strain distribution of the threading dislocation affects the electronic structure. Moreover, the ground state transition behaviour is also influenced by the position of the adjacent threading dislocation.

关键词： quantum dot threading dislocation electronic structure absorption efficiency

Optimized optical phase conjugation conf iguration for f iber nonlinearity compensation in CO-OFDM systems

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Chinese Optics Letters 2011年第6期9卷 31-35页

作者：李炉焦乔耀军纪越峰 key laboratory of information photonics and optical communications Ministry of Education Beijing University of Posts and Telecommunications

The optimized optical phase conjugation （OPC） configuration is proposed for the 40-Gb/s CO-OFDM system. The proposed configuration for nonlinear cancellation is systematically depicted in transmission links with lumped amplification. Numerical simulations are performed to demonstrate effectiveness. Simulation results show that mid-span spectral inversion （MSSI） can partially compensate for nonlinear distortions. Moreover, its optimized configuration can further improve system performances and increase nonlinear compensation effectiveness. Compared with MSSI, the maximal Q factor, nonlinear threshold, and transmission distance of optimized OPC configuration increase by over 1.6 dB, 2 dB, and 2 times, respectively.

关键词： optical phase conjugation Optimization Telecommunication systems

Stacking-faults-free zinc blende GaAs/AlGaAs axial heterostructure nanowires during vapor-liquid-solid growth

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Chinese Optics Letters 2011年第4期9卷 71-74页

作者：郭经纬黄辉任晓敏颜鑫蔡世伟黄永清王琦张霞王伟 key laboratory of information photonics and optical communications Ministry of EducationBeijing University of Posts and Telecommunications

Pure zinc blende structure GaAs/AlGaAs axial heterostructure nanowires （NWs） are grown by metal organic chemical vapor deposition on GaAs（111） B substrates using Au-catalyzed vapor-liquid-solid mechanism. Al adatom enhances the influence of diameters on NWs growth rate. NWs are grown mainly through the contributions from the direct impingement of the precursors onto the alloy droplets and not so much from adatom diffusion. The results indicate that the droplet acts as a catalyst rather than an adatom collector.

关键词： Adatoms Drops Gallium alloys Gold coatings Liquids Metallorganic chemical vapor deposition Nanowires Organic chemicals Organometallics Stacking faults Zinc

Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field

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Chinese Physics B 2011年第6期20卷 392-396页

作者：贾博雍俞重远刘玉敏韩利红姚文杰冯昊叶寒 key laboratory of information photonics and optical communications (ministry of education) Beijing University of Posts and Telecommunications

The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.

关键词： quantum ring electron state donor impurity uniform magnetic field

Design and analysis of flexible colorless remote node using RSOA-assisted Michelson interferometer

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Chinese Optics Letters 2011年第2期9卷 23-26页

作者：刘磊张民刘明涛张小频叶培大 key laboratory of information photonics and optical communications Ministry of EducationBeijing University of Posts and Telecommunications

A scheme of flexible colorless remote note with reflective semiconductor optical amplifier （RSOA） assisted Michelson interferometer is proposed. This is capable of generating an optical carrier suppressed signal at a specific radio frequency to suppress the penalty brought about by Rayleigh backscattering and reflection in a full-duplex single fiber transmission network. Simulations are conducted, and the validation of the proposal is discussed by observing the penalty eye opening factor. The results are useful for designing cost-effective multi-wavelength passive optical network （PON） or radio-over-fiber （RoF） systems.

关键词： Fiber optic networks Michelson interferometers optical instruments Radio broadcasting Radio transmission Semiconductor optical amplifiers