Locking bandwidth and birefringence effects for polarized optical injection in vertical-cavity surface-emitting lasers

The aim of this paper is to investigate the effects of external optical injection taking account of polarization and electron spin properties in vertical-cavity surface-emitting lasers (VCSELs). Using external polarized injection we seek the locked phases and amplitudes of specific polarized fields in terms of injection level and frequency detuning, taking account of two kinds of distinguishable carrier density (spin-up and spin-down). For the conventional form of optical injection without taking account of spin-polarized fields there are three fundamental equations describing the carrier density, field amplitude and phase. However, by using the spin flip model (SFM), the combined effect of polarized fields along two perpendicular crystal axes and electron spin properties results in six equations. We analyse the conditions for stable locking and also the influence of birefringence effects on the stability map of detuning versus optical injection for both cases of injection polarized parallel and perpendicular to the lasing mode of the solitary VCSEL. For given values of pumping and spin relaxation rate there is a minimum birefringence rate for orthogonal injection. Above this value three regions of elliptical polarization are found in the stability map, namely “quasi-stability” (QS), “coupled limit cycle” (CLC) and “coupled chaos” (CC). The three regions of linear polarization, namely chaos, limit cycle and stability, are reduced in area compared to the case of parallel injection. For orthogonal injection it is found that increased birefringence or reduced spin relaxation rate causes the stable locking region to begin at higher injected power and frequency detuning.     

Dark and anti-dark vector solitons of the coupled modified nonlinear Schrödinger equations from the birefringent optical fibers

Coupled modified nonlinear Schr?dinger (CMNLS) equations describe the pulse propagation in the picosecond or femtosecond regime of the birefringent optical fibers. A new type of the Lax pair and another hierarchy of the infinitely many conservation laws are derived based on the Wadati-Konno-Ichikawa system. By means of the Hirota method, soliton solutions in the normal dispersion regime are obtained. Parametric regions for the existence of dark and anti-dark vector soliton solutions are given. Asymptotic analysis shows that the collision between two solitons (two anti-dark solitons, two dark solitons, or dark and anti-dark solitons) in each polarization direction is elastic. Moreover, there is no energy transfer between two polarization components of each vector soliton, whether dark or anti-dark vector soliton. In addition, dark and anti-dark solitons can coexist on the same background seen from the collision between the dark and anti-dark solitons in one polarization direction. Our graphical analysis shows that the parameters in the CMNLS equations not only determine the regions for the existence of dark and anti-dark soliton solutions but also control the phase and direction of the propagation of the solitons. Finally, through the linear stability analysis, the modulational instability condition is given.     

SU(2)非自治系统中的互补混沌——加速器中离子极化的稳定性

利用SU(2)代数动力学方程研究了加速器中带自旋离子的极化对磁场的含时无规扰动的稳定性问题,发现低度极化的系统对磁场无规扰动十分敏感,而高度极化的系统对磁场无规扰动比较稳定;自旋守恒导致自旋纵向分量的无规涨落和横向分量的无规涨落存在着互补性.这一结果表明,在产生离子束极化的实验中,在离子束低度极化的前期阶段,磁场应具有较高的稳定性,而在离子束极化度较高的后期阶段,磁场的稳定性要求可以放松;自旋纵向分量的无规涨落和横向分量的无规涨落的互补性有可能用来做成稳定离子极化的负反馈.     

巨介电常数氧化物CaCu3Ti4O12的介电和阻抗特性

采用固相烧结法合成了单相巨介电常数氧化物CaCu₃Ti₄O₁₂（CCTO）.用阻抗分析仪分析了10—420 K温度范围内的介电频谱和阻抗谱特性,并结合ZVIEW软件进行了模拟.结果表明：温度高于室温时,频谱出现两个明显的弛豫台阶,低频弛豫介电常数随温度升高而显著增大,表现出热离子极化特点;温度低于室温时,频谱表现出类德拜弛豫,且高、低平台介电常数值基本不随温度变化,表现出界面极化特点和较好的温度稳定性.频谱中依次出现的介电弛豫对应于阻抗谱中 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 介电频谱 阻抗谱 Cole-Cole半圆弧     

光源偏振度对光纤陀螺零漂影响的研究

以Y波导集成光学调制器保偏型干涉式光纤陀螺作为研究对象,根据各光学元器件的参数建立了各器件的琼斯矩阵以及光路传输模型,在此基础上进行了光路偏振误差的理论分析。通过推导,得到了保偏型干涉式光纤陀螺的偏振误差表达式,并首次分析了光源偏振度对光纤陀螺零漂的影响。借助光源尾纤输出的光谱,对由0%~3%之间呈线性变化的偏振度以及对经实验测试的光源偏振度的实际值引起的偏振模式耦合误差的零漂值进行了仿真计算。结果表明,当光路中其它参数不变时,由光源偏振度变化引起的零漂值为0.001°/h,满足了高精度光纤陀螺的精度要求。     

Metal contact effect on the persistent internal polarization in pure and doped polystyrene

Photo-electrets of pure and copperphthalocyanine doped polystrrene films (thickness 20 μm) were formed by UV- radiation in an electric field with Al, Cu, Ni, Zn, Cd and Pb as electrode materials. The depolarization current and the released charge show a strong dependence on the material of the electrode. Two distinct regions in the current decay characteristic indicate that the polarization consists of trapped holes and electrons. The amount of charge injected increases with decreasing work function of the contact metal. Doping increases the stability of the charge.     

Constraining the Kähler Moduli in the Heterotic Standard Model

Phenomenological implications of the volume of the Calabi-Yau threefolds on the hidden and observable M-theory boundaries, together with slope stability of their corresponding vector bundles, constrain the set of Kähler moduli which give rise to realistic compactifications of the strongly coupled heterotic string. When vector bundles are constructed using extensions, we provide simple rules to determine lower and upper bounds to the region of the Kähler moduli space where such compactifications can exist. We show how small these regions can be, working out in full detail the case of the recently proposed Heterotic Standard Model. More explicitly, we exhibit Kähler classes in these regions for which the visible vector bundle is stable. On the other hand, there is no polarization for which the hidden bundle is stable.     

Intensity and polarization self-pulsations in vertical-cavity surface-emitting lasers

We implement a dynamic model that describes the polarization behavior in vertical-cavity surface-emitting lasers that contain an absorbing region surrounding the active zone. We find four regions of qualitatively different behavior: stable linearly polarized operation, intensity pulsations of a linearly polarized component, pulsations of both total-intensity and polarization components, and polarization self-pulsation with constant total intensity. We characterize the four regions by computing the polarization-resolved optical and power spectra. The predicted behavior agrees with recent experimental results.     

Effect of scattering anisotropy and material optical anisotropy of oriented fiber layers on the transmitted light polarization

The effect of polarization-dependent attenuation and birefringence of media composed of oriented fibers on the transmitted light polarization has been experimentally investigated in the visible and IR regions using the polarimetric technique based on the rotational-invariant representation. A comparison of the experimental results obtained for structures composed of layers of oriented glass and 30-μm polypropylene fibers suggests that the contributions of the polarization-dependent attenuation and birefringence of the medium to the transmitted-light polarization parameters can be differentiated. For rat-skin tissue samples, the contribution of the polarization-dependent attenuation to the polarization parameters in the visible and near-IR spectral regions is negligible.     

通道调制型偏振成像系统的偏振参量重建

通道调制型偏振成像系统中,焦平面上获取的信息需要通过目标偏振参量的重建才能有效提取,因而重建是目标识别、材料分析、生物医疗等技术进一步应用的前提.为了实现在非理想情况下通道调制型偏振成像系统的偏振参量精确重建,需要解决成像系统中电荷耦合器件(CCD)采样频率与频谱位置偏移对重建的影响.本文首先详细分析了频谱不发生混叠的条件:CCD采样频率应至少为4倍基频;在偏振干涉频谱位置偏移时,使用最大频谱法确定各个偏振态的载波频率,通过频移、滤波和傅里叶变换获得目标的偏振重建二维图像;最后通过计算机模拟仿真与实验分析结合的方法验证该重建方案的可行性与有效性.模拟与实验结果表明:改进后的偏振重建法得到的偏振图像与原始输入图像的均方差在0.001以下,峰值信噪比有明显的提高,且结构相似度可达到0.9以上,表明该方法获得的二维偏振态重建图像精度高,与理论偏振解调法相比具有很大的优越性.该工作希望为后续偏振探测与分析进一步的研究提供参考.     

谐波锁模掺铒光纤激光器的稳定性研究

对谐波锁模掺铒光纤激光器的稳定性进行了实验研究.采用再生锁模技术控制腔长变化对稳定性的影响,提出了在腔内利用缠绕光纤法替代保偏光纤以获取偏振稳定机制的方案,并进行了相关实验.利用自相位调制＋频谱滤波抑制超模噪音,实验中当抽运功率在50 mW以上时就足可以抑制超模噪音.实验结果表明:采用以上三种措施能够较好地解决影响谐波锁模光纤激光器稳定的温漂、偏振起伏和超模噪音问题,从而大大提高了谐波锁模光纤激光器的稳定性.     

可调谐型金属线栅偏振器的特性研究

金属线栅偏振器是一种新兴的基于微纳结构的光学偏振器件, 体积小、性能高、易集成.但在紫外和可见光波段, 通过缩小线栅的特征尺寸来提高消光比的方法已经受到纳米制作工艺的限制, 因此需要新的结构来提高其偏振特性.双层金属线栅结构仅在特定波段上提高 器件的偏振特性. 在此基础上, 提出一种间距可调谐的金属线栅偏振器结构, 通过调谐两层金属线栅之间的距离来确保偏振器极高的消光比和很强的透过率. 利用VirtualLab软件的傅里叶模式方法, 计算了可调谐型金属线栅偏振的透过率和消光比. 数值仿真结果表明, 双层可调谐型金属线栅结构在整个紫外、 可见光波段极大地提高了透射光的消光比和透过率. 关键词： 线栅偏振器 可调谐结构 消光比 压电陶瓷     

Polarization and transverse-mode dynamics of gain-guided vertical-cavity surface-emitting lasers

Transverse-mode competition and polarization selection in gain-guided vertical-cavity surface-emitting lasers are studied by use of a transverse continuous model that incorporates basic physical mechanisms of polarization dynamics. Polarization stability and polarization switching within the fundamental Gaussian mode are described. The first-order transverse mode always starts lasing orthogonally polarized to the fundamental one. At larger currents polarization coexists with several active transverse modes. These results are shown to be sensitive to the carrier spin-flip relaxation rate.     

Self-focusing dynamics of polarization vortices in Kerr media

We investigate numerically and experimentally the spatial collapse dynamics and polarization stability of radially and azimuthally polarized vortex beams in pure Kerr medium. These beams are unstable to azimuthal modulation instabilities and break up into distinct collapsing filaments. The polarization of the filaments is primarily linear with weak circular components at the filaments' boundaries. This unique hybrid linear-circular polarization collapse pattern persists to advanced stages of collapse and appears to be a general feature of beams with spatially variant linear polarization.     

Properties unique in nuclei far from β stability line

Nucleons with very small binding energies present in nuclei far from the β stability line produce a unique shell structure, which leads to the disappearance of traditional magic numbers or to the creation of new magic numbers and new deformation regions. We study the shell structure in terms of the variation of two important ingredients, the kinetic energy and the spin-orbit splitting, as a function of the orbital angular momentum ℓ, when binding energies of neutrons decrease towards zero. It is also shown that for low-lying threshold strength, a negative sign is possible for the polarization charge coming from the coupling of one-particle to isoscalar shape oscillations. Received: 1 May 2001 / Accepted: 4 December 2001     

Properties of laser gain of Li:CdZnO/ZnMgO quantum well

The many-body optical gain in Li:CdZnO/MgZnO quantum well (QW) structures with spontaneous polarization and piezoelectric polarization, and ferroelectric dipole moment is investigated by using the non-Markovian gain model with many-body effects. The CdZnO/MgZnO QW structure with high Cd composition is found to have smaller optical gain because the strain-induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd. The internal field is reduced due to the additional polarization by Li in the CdZnO/MgZnO QW structure. These results show that Li:CdZnO-based QW lasers are promising candidates for optoelectric applications in visible and UV regions.     

Discontinuous Galerkin methods for dispersive and lossy Maxwell's equations and PML boundary conditions

In this paper, we will present a unified formulation of discontinuous Galerkin method (DGM) for Maxwell's equations in linear dispersive and lossy materials of Debye type and in the artificial perfectly matched layer (PML) regions. An auxiliary differential equation (ADE) method is used to handle the frequency-dependent constitutive relations with the help of auxiliary polarization currents in the computational and PML regions. The numerical flux for the dispersive lossy Maxwell's equations with the auxiliary polarization current variables is derived. Various numerical results are provided to validate the proposed formulation.     

全光纤量子通信系统中的高速偏振控制方案

偏振控制在光通信中是至关重要的技术, 关系着通信系统的稳定性和误码率. 本文提出一种基于双向Sagnac环工作方式的全光纤高速偏振控制方案, 通过调节环中一个光纤电光相位调制器的相位差而精确控制光场偏振方向, 并且实现了单个端口输出各种偏振态, 无需后续耦合操作. 相位控制精度为10^-3 rad, 最大消光比可达30 dB, 工作速率可达2 GHz. 由于本方案的精度、调制速度和稳定性都很高, 并采用了器件简单、成本低廉的全光纤光路, 易于集成, 在量子保密通信等光通信领域中有很好的应用前景. 关键词： 光纤偏振控制器 Sagnac环 量子通信     

Enhancement of optical gain in Li:CdZnO/ZnMgO quantum well lasers

The CdZnO/ZnMgO QW structure with high Cd composition is found to have smaller optical gain because the strain-induced piezoelectric polarization and the spontaneous polarization in the well increase with the inclusion of Cd. The internal field is reduced due to the additional polarization of opposite direction by Li in the CdZnO/ZnMgO QW structure. These results show that Li:CdZnO-based QW lasers are promising candidates for optoelectric applications in visible and UV regions.     

Output polarization states of a corner cube reflector irradiated at non-normal incidence

A method has been developed for determining the polarization state of the retro-reflected beam from a corner cube irradiated with an input beam of arbitrary polarization state and of arbitrary tilt angle to the cube. Experimentally, the output beam consists of six distinct beamlets of different polarization states that are focused into six non-overlapping regions in the active area of the detector. The overall polarization state of the beam as measured by the photodetector can thus be represented by the incoherent superposition of the polarization states of the six beamlets. Experiments have been performed that verify the theory for a linearly polarized input beam irradiating the corner cube.