拉曼效应对低双折射光纤偏振特性的影响

在低双折射光纤中,利用线偏振光满足的包含拉曼效应的非线性耦合模传输方程,通过引入斯托克斯参量,导出了斯托克斯参量所满足的耦合模传输方程.利用庞加莱球图示法,描述了拉曼增益效应作用下光波偏振态的演化,研究分析了拉曼效应对低双折射光纤中光波偏振态演化规律的影响.结果表明,当输入功率与运动常量满足一定关系时,拉曼增益效应改变了光波传输时其偏振态演化周期和偏振态的椭圆率.     

基于非线性偏振旋转的全正色散锁模光纤激光器偏振特性的研究

基于耦合的Ginzburg-Landau方程和各器件的琼斯矩阵,建立了全正色散锁模光纤激光器的数值模型,计算了腔内各点脉冲不同部分的偏振态。计算结果表明,当线性双折射较强时,光纤中脉冲的偏振态近似以拍长为周期变化,一个拍长内的演化过程为右旋椭圆偏振光-线偏振光-左旋椭圆偏振光-线偏振光-右旋椭圆偏振光。与一般的饱和吸收体不同,非线性偏振旋转等效饱和吸收体的调制深度随波片角度变化。计算了波片方位角改变时,调制深度的变化情况。相比于偏振分束器之前的1/2波片及1/4波片,偏振分束器之后的波片对调制深度的影响更大。     

一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法

提出和论述了一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法。基本思想是设计和采用一种全光学偏振态转换器 ,理论上能将随机偏振态的输入信号光转换为固定偏振方向且功率基本不变的线偏振光 ,利用它控制信号光的偏振态能够克服四波混频过程所固有的偏振敏感性。将这种方法与正交偏振双抽运方法结合起来 ,能较简单地实现偏振不敏感且具有近似常数转换效率的宽带四波混频光波长转换     

基于LabVIEW的光偏振态转换及检测仿真设计

利用LabVIEW软件设计了光偏振态转换以及检测的仿真系统,该系统可实现线偏振光、圆偏振光、椭圆偏振光、非偏振光和部分偏振光的电场振动面的实时显示,并且能够准确仿真出半波片、1/4波片以及偏振片等偏振转换器件对光偏振状态的转换,最后还能实现偏振光的强度检测仿真.     

一各新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法

提出和论述了一种新颖的偏振不敏感的基于半导体光放大器的四波混频光波长转换方法，基本思想是设计和采用一种全光学偏振态转换器，理论上能将随机偏振态的输入信号光转换为固定偏振方向且功率基本不变的线偏振光，利用它控制信号光的偏振态能够克服四波混频过程所固有的偏振敏感性，将这种方法与正交偏振双轴运方法结合起来，能较简单地实现偏振不敏感且具有近似常数转换效率的宽带四波混频光波长转换。     

油雾扩散过程中浓度对偏振激光传输特性的影响

针对大气环境中粒子浓度对激光传输过程的影响问题,以油雾粒子为研究对象,利用油雾粒子在扩散过程中产生的非均匀环境,进行了偏振激光传输的半实物仿真实验。实验采用532 nm激光器,分别研究了水平线偏振光、45°线偏振光以及左旋圆偏振光在油雾扩散过程中偏振态的变化情况。利用粒度仪对扩散环境进行了量化标定。实验结果表明:在油雾扩散过程中,浓度越高,偏振度变化的随机性越大,圆偏振光的保偏性优于线偏振光。在相同浓度下,0°线偏振光对偏振态的保持性要优于45°线偏振光。在浓度极高的情况下,体积浓度为2 mg/L及其以上时,线偏振光与圆偏振光的保持性趋向一致。     

光的偏振性对Hanbury Brown-Twiss实验的影响

在理论和实验上研究了完全偏振光的不同偏振态和光的偏振度对Hanbury Brown-Twiss实验二阶关联函数g(2)的影响.实验中用线偏振光通过1/4波片获得椭圆偏振光,并通过旋转波片实现对完全偏振光偏振态的改变;用两柬振动方向相互垂直,传播方向相同且相位差随机的线偏振光合成部分偏振光,并通过调节一束光的光强实现对合成光偏振度的改变.结果表明:对于完全偏振光,其偏振态的改变对g(2)没有影响;对于不同偏振度P的光源,g(2)为P的二次函数.特殊地,自然光情况下P=0,g(2)的理论最大值为1.5;完全偏振光情况下P=1,g(2)的理论最大值为2.理论与实验符合得较好.     

拉曼效应对低双折射光纤偏振态的影响

在准连续情况下, 通过求解低双折射光纤中含有拉曼效应的右旋与左旋圆偏振光所满足的耦合非线性薛定谔方程,着重研究了低输入功率和高输入功率情形在加入拉曼效应前后, 有效偏振拍长和输入功率的变化关系. 结果表明: 无论入射光的偏振是沿着慢轴或沿着快轴, 拉曼效应均改变了入射光偏振态演变的周期, 同时改变了入射光的传输距离.     

拉曼效应对低双折射光纤偏振态的影响

在准连续情况下,通过求解低双折射光纤中含有拉曼效应的右旋与左旋圆偏振光所满足的耦合非线性薛定谔方程,着重研究了低输入功率和高输入功率情形在加入拉曼效应前后,有效偏振拍长和输入功率的变化关系.结果表明:无论入射光的偏振是沿着慢轴或沿着快轴,拉曼效应均改变了入射光偏振态演变的周期,同时改变了入射光的传输距离.     

基于矩阵理论的螺旋液晶透射光偏振态研究

将螺旋型液品看作是N层双折射材料晶片叠合而成,而每层光轴相对于相邻的晶片有一个小的旋转.本文基于矩阵理论,研究了光在螺旋液晶中传输时偏振态的变化.经过详细的数学推导,理论研究表明.线性偏振光经过螺旋液晶后偏振态会发生改变.当满足一定的条件时,线偏振光的偏振方向旋转90°,左旋圆偏振光经过左旋螺旋液晶后转变为右旋圆偏振光.     

Optical Bloch equations with dual photon excitation explain the polarization dependence of four wave mixing quantum beats

We explain the polarization dependence of four wave mixing (FWM) quantum beats for semiconductors as essentially due to the spin phase correlations of photo-excited electrons, rather than to Coulomb interaction between the electrons. A theoretical analysis is given within the framework of optical Bloch equations for the light–semiconductor interactions and the Luttinger–Kohn model for the band structure. Residual Coulomb interactions between charge carriers are ignored. The results suggest that the polarization dependence of FWM quantum beats is a purely coherent effect of dual photon excitations, rather than, e.g., exciton–exciton Coulomb interaction. We show that the coherence transfer between the excited states is responsible for the FWM in a configuration with orthogonally polarized pump and probe.     

Monopolar optical orientation of electron spins in bulk semiconductors and heterostructures

It is shown that intraband absorption of circularly polarized light leads to spin polarization of the electron gas. A theory of this monopolar optical spin orientation is developed for indirect intraband transitions in bulk semiconductors and for indirect intrasubband and direct intersubband transitions in quantum wells.     

Valley selection by linear optical pumping in PbTe

Due to the anisotropy of optical matrix elements, selective population of valleys is possible in multivalley semiconductors under linearly polarized light excitation. We observe this effect by measuring the linear polarization ratio of recombination light of a PbTe sample at low temperature.     

Ultrafast light-induced magnetization dynamics of ferromagnetic semiconductors

We develop a theory of ultrafast light-induced magnetization dynamics in ferromagnetic semiconductors. We demonstrate magnetization control during femtosecond time scales via the interplay between nonlinear circularly polarized optical excitation, hole-spin damping, polarization dephasing, and Mn-hole-spin interactions. Our results show magnetization relaxation and precession for the duration of the optical pulse governed by the nonlinear optical polarizations and populations.     

Measurement of electron spin lifetime and optical orientation efficiency in germanium using electrical detection of radio frequency modulated spin polarization

We propose and demonstrate a technique for electrical detection of polarized spins in semiconductors in zero applied magnetic fields. Spin polarization is generated by optical injection using circularly polarized light which is modulated rapidly using an electro-optic cell. The modulated spin polarization generates a weak time-varying magnetic field which is detected by a sensitive radio-frequency coil. Using a calibrated pickup coil and amplification electronics, clear signals were obtained for bulk GaAs and Ge samples from which an optical spin orientation efficiency of 4.8% could be determined for Ge at 1342 nm excitation wavelength. In the presence of a small external magnetic field, the signal decayed according to the Hanle effect, from which a spin lifetime of 4.6±1.0 ns for electrons in bulk Ge at 127 K was extracted.     

Effect of Carrier Differences on Spin Polarized Injection into Organic and Inorganic Semiconductors

Spin polarized injection into organic and inorganic semiconductors are studied theoretically from the spin diffusion theory and Ohm＇s law, and the emphases are placed on the effect of the carrier differences on the current spin polarization. The mobility and the spin-flip time of carriers in organic and inorganic semiconductors are different. From the calculation, it is found that current spin polarization at a ferromagnetic/organic interface is higher than that at a ferromagnetic/inorganic interface because of different carriers in them. Effects of the conductivity matching, the spin dependent interracial resistances, and the bulk spin polarization of the ferromagnetic layer on the spin polarized injection are also discussed.     

Four-photon polarization spectroscopy of induced plasma oscillations in a skin layer of semiconductors

Probe-beam scattering spectra have been obtained for four-wave mixing of laser waves in the skin layer of intrinsic semiconductors. The spectra were recorded using the frequency dispersion of orthogonally polarized radiation, which arises as a result of nonlinear optical interaction with conduction-band electrons. The mixing of two counterpropagating light waves in a semiconductor, implemented under nonlinear excitation of longitudinal density oscillations in the plasma electron subsystem of the semiconductor, is theoretically considered. This mixing is shown to lead to the rotation of the probe-beam polarization vector. The results obtained are of interest, e.g., for studying optical metamaterials based on thin-film structures.     

Current-induced spin polarization in strained semiconductors

The polarization of conduction electron spins due to an electrical current is observed in strained nonmagnetic semiconductors using static and time-resolved Faraday rotation. The density, lifetime, and orientation rate of the electrically polarized spins are characterized by a combination of optical and electrical methods. In addition, the dynamics of the current-induced spins are investigated by utilizing electrical pulses generated from a photoconductive switch. These results demonstrate the possibility of a spin source for semiconductor spintronic devices without the use of magnetic materials.     

单模光纤中线偏振皮秒脉冲光的光致多脉冲现象的新解释

结合单模光纤的本征线性双折射与非线性双折射效应，利用二偏振分量的耦合方程对单模光纤中线偏振皮秒脉冲光的光致多脉冲现象作出了解释，得到的计算结果与实验符合得很好。