Parity-time对称性对电注入半导体激光器的模式控制

非厄米的描述对于开放系统有重要意义,满足parity-time对称性的哈密顿量,其参数在一定范围内可以使能量具有实的本征值.本文通过模拟,研究了损耗大小以及结构对称性对条形波导中的parity-time对称性的影响,并通过实验发现了电注入条件下由parity-time对称破缺导致的脊条波导模式间隔加倍、模式数减半的现象.     

单负材料组成一维光子晶体双量子阱结构的共振模

通过传输矩阵方法, 计算模拟了两种单负材料组成一维光子晶体双量子阱结构的透射谱. 研究发现: 由于双量子阱结构双阱之间的相互耦合作用, 共振模发生双重劈裂, 共振峰之间的距离可以通过调节双阱之间的耦合强度控制, 共振模的品质因子可以通过调节外部障碍光子晶体的周期数控制. 并且, 共振模受入射角和光偏振模式的影响都比较小, 适合全方向滤波. 当考虑两种单负材料不同损耗的影响时, 研究结果表明, 电损耗对低频处的共振模影响大, 而磁损耗对高频和低频处的共振模影响都比较大.     

Soliton dynamical properties of Boseben Einstein condensates trapped in a double square well potential

We first present an analytical solution of the single and double solitions of Bose-Einstein condensates trapped in a double square well potential using the multiple-scale method. Then, we show by numerical calculation that a dark soliton can be transmitted through the square well potential. With increasing depth of the square well potential, the amplitude of the dark soliton becomes larger, and the soliton propagates faster. In particular, we treat the collision behaviour of the condensates trapped in either equal or different depths of the double square well potential. If we regard the double square well potential as the output source of the solitons, the collision locations (position and time) between two dark solitons can be controlled by its depth.     

Pseudospin symmetry and a double ring-shaped spherical harmonic oscillator potential

A new double ring-shaped spherical harmonic oscillator potential is presented. The pseudospin symmetry in this system is investigated by solving the Dirac equation with equal mixture of scalar and vector potentials with opposite signs. The normalized spinor wave function and energy equation are obtained and some particular cases are discussed.      

Intersubband transitions and refractive index changes in coupled double quantum well with different well shapes

In this study, both the linear intersubband transitions and the refractive index changes in coupled double quantum well (DQW) with different well shapes for different electric fields are theoretically calculated within framework of the effective mass approximation. Results obtained show that intersubband transitions and the energy levels in coupled DQW can importantly be modified and controlled by the electric field strength and direction. By considering the variation of the energy differences, it should point out that by varying electric field we can obtain a blue or red shift in the intersubband optical transitions. The modulation of the absorption coefficients and the refractive index changes which can be suitable for good performance optical modulators and various infrared optical device applications can be easy obtained by tuning applied electric field strength and direction.     

Resonant modes and inter-well coupling in photonic double quantum well structures with single-negative materials

We investigate the resonance tunneling modes of photonic double quantum well made of two photonic crystals with two different single-negative materials. It is found that these resonance modes split pairs, due to a coupling between two photonic wells. It is observed that when two photonic quantum wells are far away from each other, resonance modes appear as a single peak. And the quality factors of the transmittance resonance peaks can be greatly improved by increasing the period number of the outer barrier. The effects of the losses coming from ENG and MNG materials on the resonance modes are also specifically explored.     

Dispersive Properties of tunnelling—induced transparency in an asymmetric double quantum well

We have investigated the dispersive properties of tunnelling-induced transparency in asymmetric double quantum well structures where two excited states are coupled by resonant tunnelling through a thin barrier in a three-level system of electronic subbands. The intersubband transitions exhibit high dispersion at zero absorption, which leads to the slow light velocity in this medium as compared with that in vacuum (c=3×10⁸). The group velocity in a specific GaAs/AlGaAs sample is calculated to be v_g=c/4.30. This structure can be used to compensate for the dispersion and energy loss in fibre optical communications.     

Observation of arc modes in a magnetically rotating arc plasma generator

An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high‐temperature plasma zone, which indicates that the diffuse mode may be more useful in industry.     

Intersubband transitions in an asymmetric double quantum well

The intersubband optical absorption in an asymmetric double quantum well for different barrier widths and the right well widths are theoretically calculated within the framework of effective mass approximation. The results obtained show that the intersubband transitions and the energy levels in an asymmetric double quantum well can be importantly modified and controlled by the barrier width and the well width. The sensitivity to the barrier and well widths of the absorption coefficient can be used in various optical semiconductor device applications.