Phase-Controlled Transparent Superluminal Light Propagation in a Doppler-Broadened Four-Level N-Type System

The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence(SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self- and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature,the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.     

Role of anisotropy on the domain wall properties of ferromagnetic nanotubes

In this paper we investigate the role of magneto-crystalline anisotropy on the domain wall (DW) properties of tubular magnetic nanostructures. Based on a theoretical model and micromagnetic simulations, we show that either cubic or uniaxial magneto-crystalline anisotropies have some influence on the domain wall properties (wall size, propagation velocity and energy barrier) and then on the overall magnetization reversal mechanism. Besides the characterization of the transverse and vortex domain wall sizes for different anisotropies, we predict an anisotropy dependent transition between the occurrence of transverse and vortex domain walls in tubular nanowires. We also discuss the dynamics of the vortex DW propagation gradually increasing the uniaxial anisotropy constant and we found that the average velocity is considerably reduced. Our results show that different anisotropies can be considered in real samples in order to manipulate the domain wall behavior and the magnetization reversal process.     

水平极化光在单轴吸收晶体中的传播

根据光在各向同性吸收介质中传播的分析方法,引入了波法线矢量传播常量,讨论了水平极化光在单轴吸收晶体中的传播规律,得到了波法线折射率、光线折射率、吸收系数等描述吸收晶体性质和光传播性质的物理量的表达式,推导出透明晶体的相应公式.数值计算表明,由该法得到的晶体表面的反射和透射系数与用复折射率表示法得到的结论一致.     

天气对光散射传输影响的仿真分析

天气对光散射传输影响分析具有很好的实践指导意义。目前均用单次散射模型研究非视线光传输信道特性,但该方法在天气条件差或者传输距离较远时误差很大。利用蒙特卡罗方法进行了基于多次散射的非视线光传输模拟,对多种天气条件下(晴、阴、雨和雾等)不同距离光散射传输进行仿真。结果表明,中远距离散射传输时,大气衰减起主导作用,信号传输质量由晴、阴、雨、雾依次降低;近距离散射传输时,受到大气衰减和散射的共同作用,天气对光散射传输的影响较小。因此,大气光散射传输技术可作为短距离条件下实现全天候通信的一种新方式。     

强非局域介质中1+1维高斯型损耗空间双孤子的相互作用

研究了1+1维高斯型双光束在含小损耗的强非局域非线性介质中的传输特性。通过对该介质中光束传输遵循的非局域非线性薛定谔方程进行近似简化,得到了含小损耗强非局域非线性介质中1+1维高斯型双光束传输模型。在此基础上运用解析的方法研究了双光束传输的演化规律,得到了准双孤子解。经过进一步分析发现,在传输过程中两光束中心的轨迹为艾里函数;两光束会准周期性地碰撞、分离;随着传输距离的增大,两光束中心之间的最大距离会越来越大。另一方面,当损耗逐渐增大时,两光束的碰撞空间周期将变短,同时两光束中心之间的最大距离也越来越大。     

Manifestation of spin-orbital interaction of a photon

The review of the effects which can be considered as manifestation of spin-orbital interaction of a photon (mutual influence of light polarization and propagation) has been presented. The effect of polarization influence on propagation and the effect of the propagation influence on polarization under light propagation through locally isotropic inhomogeneous medium have been described. The notion of spin and angular momentum of a photon and their conversion into mechanical momentum have been discussed. The experimental conditions which are suitable for investigation of spin-orbital interaction under light propagation through optical fiber have been described.     

Slow light with cavity electromagnetically induced transparency

We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of approximately 200 ns was observed in the cavity and Rb EIT system, which is approximately 70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.     

Light Propagation in an Inhomogeneously Absorbing Medium: Near Field of GaAs-Light Emitting Diodes

The light propagation in media with inhomogeneous absorption is investigated by solving the wave equation in the approximation of very short wavelengths. The lowest order correction of the straight-on light propagation is given. In the approximation of light rays the near-field intensity of a light emitting diode (LED) is calculated by using a special absorption function within the region of light excitation.     

Absorption-free superluminal light propagation in a quantum-dot molecule

The propagation of a weak probe field in a three-level quantum-dot molecule is investigated by employing the tunnel coupling. It is shown that in the absence of tunnel coupling, the propagation of light pulse is superluminal, similar to a simple two-level system. A high-resolution dip appears in optical spectra due to the presence of tunnel coupling. We show that this narrow dip leads to the subluminal light propagation with doublet absorption, so the group velocity of a light pulse can be controlled by interdot tunnel coupling. It is also demonstrated that by applying an indirect incoherent pumping field to the probe transition, the absorption doublet switches to the gain doublet and then the absorption-free superluminal light propagation is appeared.     

Absorption-free superluminal light propagation in a quantum-dot molecule

The propagation of a weak probe field in a three-level quantum-dot molecule is investigated by employing the tunnel coupling. It is shown that in the absence of tunnel coupling, the propagation of light pulse is superluminal, similar to a simple two-level system. A high-resolution dip appears in optical spectra due to the presence of tunnel coupling. We show that this narrow dip leads to the subluminal light propagation with doublet absorption, so the group velocity of a light pulse can be controlled by interdot tunnel coupling. It is also demonstrated that by applying an indirect incoherent pumping field to the probe transition, the absorption doublet switches to the gain doublet and then the absorption-free superluminal light propagation is appeared.     

Electromagnetic field in a slab of photonic crystal by BPM

The finite-difference vector beam propagation method is used to simulate propagation of Gaussian light beam in a finite slab of photonic crystal. A possibility to control light flow by the change of symmetry and polarisation of the incident light beam is demonstrated.     

蔗糖溶液折射率与浓度关系的理论和实验探究

光在介质中的传播遵循费马原理.在均匀介质中光沿直线传播,非均匀介质中,光的传播轨迹比较复杂.本文以蔗糖溶液为研究对象,设计了光在非均匀介质中传播实验,建立了相关模型,理论分析了溶液折射率随深度(浓度)变化的关系.进行了数据拟合,得出溶液折射率随液体深度变化的表达式.     

Group velocity manipulation in active fibers using mutually modulated cross-gain modulation: from ultraslow to superluminal propagation

We propose and experimentally demonstrate the propagation of slow/fast light in an erbium-doped fiber (EDF) using mutually modulated cross-gain modulation. The group velocity of the light signal can be manipulated by the effect of gain cross-saturation modulation by a saturating light at an arbitrary wavelength in the gain bandwidth of the EDF. The ultraslow propagation with a small group velocity of 5.6 × 10?3c (c is the light speed in free space) and superluminal propagation with a negative group velocity of -1.1 × 10?3c has been observed under different modulation phases.     

The effect of grana and inter-grana components of chloroplasts on green light transmission: A preliminary study

In this paper we simulate for the first time the propagation of green light through grana and inter-grana components of chloroplasts. Those components are nano-metric structures and thus regular estimation of the propagation of light cannot be exact without taking into account diffraction effects. The numerical investigation presented in this paper solves Maxwell wave equation using the finite-difference time-domain (FDTD) numerical approach to analyze the propagation of light through a chloroplast model.     

Slow light propagation via quantum coherence in a semiconductor quantum well

With the Schrödinger equations, we investigate the low-intensity light pulse propagation through a semiconductor quantum wells. Through studying the dispersion and absorption properties of the weak probe field, it is shown that slow light propagation is observed in this system. From the view point of practical purpose, it is more advantageous than its corresponding atomic system. Such investigation of slow light propagation may lead to important practical applications in semiconductor quantum information.     

Quantum gravitational optics

In quantum theory, the curved spacetime of Einstein's general theory of relativity acts as a dispersive optical medium for the propagation of light. Gravitational rainbows and birefringence replace the classical picture of light rays mapping out the null geodesics of curved spacetime. Even more remarkably, superluminal propagation becomes a real possibility, raising the question of whether it is possible to send signals into the past. In this article, we review recent developments in the quantum theory of light propagation in general relativity and discuss whether superluminal light is compatible with causality.     

On some manifestations of similarity in multiple scattering of coherent light

The similarity of the decay tendencies of statistical moments of optical fields and their combinations (the mean intensity, the temporal correlation function of the field fluctuations and the degree of polarization) due to coherent light propagation in the disordered media has been considered by using a simple phenomenological model with exponential relaxation. A theoretical consideration has been carried out for the case of light propagation through a disordered slab using the diffusion approximation. The validity of the concept of similarity has been demonstrated in experiments with water suspensions of polystyrene spheres for the light transmission mode even in the case of non-diffusion regimes of light propagation through a scattering substance.     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论,对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式,并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关. 关键词： 部分相干平顶光束 偏振特性 相干-偏振矩阵 正多边形光阑 光阑衍射     

部分相干平顶光束经光阑衍射的偏振特性

根据光束的相干-偏振矩阵和传输理论，对部分相干平顶光束经正多边形光阑衍射的偏振特性进行了系统的研究.给出了部分相干平顶光束偏振度传输公式，并将高斯-谢尔模型光束以及部分相干平顶光束在自由空间传输的偏振度作为特例统一于一般表达式中.研究表明：部分相干平顶光束经光阑衍射的偏振特性与光阑截断参数、光束的空间相干性、衍射角、传输距离、平顶光束的阶数有关.     

用信息熵描述非线性光传输的研究

结合光束传输的薛定谔形式理论，基于量子机制的信息熵被用来描述非线性光传输，理论推导和数值模拟结果表明：信息熵及其对光传输方向的变化率可以表征光脉冲的压缩或展宽或光束的聚焦与发散，用信息熵表征非线性光传输优于对用脉（束）宽，二阶矩表征。