Spin noise spectroscopy of rubidium atomic gas under resonant and non-resonant conditions

The spin fluctuation in rubidium atom gas is studied via all-optical spin noise spectroscopy(SNS).Experimental results show that the integrated SNS signal and its full width at half maximum(FWHM) strongly depend on the frequency detuning of the probe light under resonant and non-resonant conditions.The total integrated SNS signal can be well fitted with a single squared Faraday rotation spectrum and the FWHM dependence may be related to the absorption profile of the sample.     

Continuous weak measurement and nonlinear dynamics in a cold spin ensemble

A weak continuous quantum measurement of an atomic spin ensemble can be implemented via Faraday rotation of an off-resonance probe beam, and may be used to create and probe nonclassical spin states and dynamics. We show that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement window. Removing the nonlinearity allows a nonperturbing measurement on the much longer time scale set by decoherence. The nonlinear spin Hamiltonian is of interest for studies of quantum chaos and real-time quantum state estimation.     

Polarization mode dispersion of spun fibers: an analytical solution

A simple analytical solution is derived from coupled-mode theory to describe the evolution of polarization mode dispersion (PMD) in spun fibers. For practical fibers with a beat length greater than a few meters, the solution is valid for a whole category of periodic spin profiles. We find that the PMD change factor is independent of the intrinsic birefringence of the fiber and the fiber PMD scales linearly with the fiber length in the short length regime. This solution allows us to determine phase-matching conditions for spun fibers, in which the PMD evolves periodically along the fiber. An example of determining the phase-matching conditions of sinusoidal-type spin profiles is given.     

Study of fiber-optic current sensing based on degree of polarization measurement

A novel fiber-optic current sensing scheme is proposed by converting the Faraday rotation to the optical signal's degree of polarization (DOP) change. In this scheme, the lightwave passes through a fiber resonant cavity multiply and experiences Faraday rotation simultaneously. Its main merit is immunity from the environment disturbance to the fiber used in ordinary Faraday rotation sensor. Brief theoretical analysis and simulation are given to show its basic characteristics. Experimental results are demonstrated and the feasibility of the proposed method is also shown.     

载流子复合对时间分辨法拉第旋转光谱的影响

利用二能级体系速率方程,推导了半导体中探测光探测到的法拉第旋转光谱的理论模型,发现电子-空穴对的复合对法拉第旋转信号随时间的衰减有重要影响,并利用该模型对GaAs量子阱中实验测得的法拉第旋转光谱进行拟合,得到GaAs量子阱材料中的电子自旋弛豫时间为73.5 ps,而直接利用单指数进行拟合得到的电子自旋弛豫时间仅为51.3 ps. 因此,直接利用单指数对法拉第旋转光谱进行拟合得到电子自旋弛豫时间的传统做法是不准确的. 关键词： 自旋弛豫时间 时间分辨法拉第旋转光谱 GaAs量子阱     

Fiber spin-profile designs for producing fibers with low polarization mode dispersion

Using coupled-mode theory, we develop a theoretical model to analyze the effects of fiber spin profiles on polarization mode dispersion (PMD). Constant, sinusoidal, and frequency-modulated spin profiles are examined, and phase-matching conditions are analyzed. Our analysis shows that PMD can be reduced effectively by use of frequency-modulated spin profiles.     

Temperature dependence of the intrinsic Faraday rotation of ErFeO3

The Faraday rotation of ErFeO₃ as a function of temperature was measured from ambient down to the spin reorientation region (90 to 100°K) at a wavelength of 6070 Å. The intrinsic Faraday rotation increases gradually with decreasing temperature and then drops rapidly to zero in the spin reorientation region. It is concluded that the contribution of the polarized Er³⁺ magnetic moments to the measured rotation is negligible and that the Faraday effect is due almost entirely to the magnetic moments of the Fe³⁺ ions.     

Scaling properties of polarization mode dispersion of spun fibers in the presence of random mode coupling

The scaling properties of polarization mode dispersion (PMD) in spun fibers are studied. Simple equations have been obtained to describe the scaling properties of spun fibers as a function of intrinsic fiber birefringence, spin parameters, and mode-coupling length under both optimal and nonoptimal spin conditions. In particular, a counterintuitive result is found for fibers with perfect spin optimization, in which case the fiber PMD increases as the mode-coupling length is shortened. The results are verified with direct numerical modeling.     

基于光纤反射腔的高灵敏电流传感器方案

提出了一种基于平面Y分支波导与法拉第旋镜的高灵敏度光纤电流传感器结构方案。利用两个法拉第旋镜与平面Y分支波导构成一个光纤反射腔,通过光在腔中的多次反射来增加待测电流导致的传感光纤中的法拉第相移,从而实现对微弱电流的测量。该结构方案中首次采用了平面Y分支光波导,从而可降低光路系统损耗,增加灵敏度,为微弱电流测量的工程化提供了一种可行的方法。     

Faraday rotation in a single-mode fiber with controlled birefringence

Faraday rotation within a polarization non-conserving single-mode optical fiber is used for ac magnetic field measurement. For that purpose the intrinsic fiber birefringence on the path to and from the Faraday rotation section is controlled. As control devices externally applied stress birefringence and phase retarder plates were used. With respect to magnetic field measurements on high electric potentials all control devices are placed at fiber input and output only.     

Magneto-optical observation of MnO-type antiferromagnetic spin order in EuSe

A striking change in the Faraday rotation spectrum of EuSe is reported when cooling the sample down to 1.5 K. The simultaneous increase of one maximum and the decrease of another Faraday rotation peak with decreasing temperature is interpreted within the magnetic Brillouin zone-model. The applicability of this model gives additional evidence for a MnO-type spin structure in EuSe.     

带缺陷结构的二维磁性光子晶体的数值模拟分析

利用频域有限差分方法分析了多种带缺陷结构二维磁性光子晶体（二重对称,四重对称和六重对称结构）的法拉第旋转角与椭圆率的变化特性.结果表明：在这些结构中,光波均被局域在中心缺陷处;同时,对于具有四重对称轴结构的材料,在其法拉第旋转角增加的同时,出射光波的椭圆率没有明显的增加;但对于不具有四重对称轴结构的材料,其法拉第旋转角增加的同时,出射光波的椭圆率也在增加.因此,只有在具有四重对称轴结构的二维磁性光子晶体中引入缺陷,才能很好地抑制光波偏振态的变化.这种带缺陷的二维磁性光子晶体结构有可能用于制作磁性光子晶体光 关键词： 磁光效应 二维磁性光子晶体 缺陷 频域有限差分法     

Two-dimensional optical control of electron spin orientation by linearly polarized light in InGaAs

Optical absorption of circularly polarized light is well known to yield an electron spin polarization in direct band gap semiconductors. We demonstrate that electron spins can even be generated with high efficiency by absorption of linearly polarized light in InxGa(1-x)As. By changing the incident linear polarization direction we can selectively excite spins in both polar and transverse directions. These directions can be identified by the phase during spin precession using time-resolved Faraday rotation. We show that the spin orientations do not depend on the crystal axes suggesting an extrinsic excitation mechanism.     

Torque equations for spin and orbital angular momenta of radiation fields and Faraday effect

The spin angular momentum S of light has never been linked to the Faraday rotation of light traveling in an optically active medium possessing a rotational invariance of a crystal, because there was no helicity term associated with the phase shift in the previous torque equation for S. In order to relate the change in S with time to the Faraday rotation, therefore, we derived an exact torque equation for S. As a result, a magnetic helicity term appeared in a new torque equation for S, so that one-half of the phase shift derived from the helicity term was equivalent to the Faraday rotation angle. However, the orbital angular momentum L had no relation to the Faraday rotation. It was thus clarified that the change in S with time is related to the Faraday rotation angle of light traveling in an optically active medium, owing to the appearance of the helicity term without a rotational invariance around the optical axis. It was also demonstrated theoretically that the Faraday rotation is accompanied by a torque acting on the crystal so that the total angular momentum of light and matter is conserved.     

直接检测光OFDM系统中的偏振相关损耗研究

对于高速光传输,直接检测的光正交频分复用系统（direct detection optical orthogonal frequency division multiplexing, DDO-OFDM）中的偏振相关损耗（polarization dependent loss, PDL）与偏振模色散相互作用,对系统传输带来较大影响。对DDO-OFDM系统中PDL与一阶PMD作用机理和数学模型进行了分析,并通过数字仿真加以验证。结果表明:在PDL与PMD联合作用下,对OFDM信号幅度及相位均产生影响,通过发送导频序列可有效实现信号均衡;由于输出偏振态随频率产生旋转,PMD效应一定程度上缓解PDL所致系统损伤,差分群时延为50 ps条件下,以10 Gb/s的速率在单模光纤传输480 km,DDO-OFDM系统Q值提高约0.8 dB。     

Bit-pattern-dependent polarization rotation in first-order PMD-compensated WDM systems

We demonstrate both numerically and experimentally that the phase-change due to fiber nonlinearities induces a bit-pattern-dependent rotation of the state-of-polarization which translates to uncertainty in the principal states of polarization. This effect severely limits the performance of the first-order PMD post-compensation and suggests the use of in-line compensators. Our simulation shows that fiber nonlinearities cause significant distortion (more than 4-dBm Q-penalty after 600-km transmission at 10 Gbit/s) after first-order PMD compensation. For optical powers as low as 3 dBm/channel in systems where PMD is not uniformly distributed along the transmission link, first-order PMD compensation may be ineffective.     

单模光纤二阶偏振模色散的Jones矩阵

利用单模光纤PMD矢量与Jones矩阵之间的关系,推导了由该矢量表示的光纤二阶PMD的Jones矩阵解析表达式,利用该矩阵可以确定输出端时域脉冲在二阶PMD近似下的表达式,并由此仿真二阶PMD对信号传输质量的影响.通过比较输入与输出信号脉冲波形和眼图发现,随着传输速率和传输距离的增加输出信号劣化.最后结果表明,当主偏振态的旋转速率为零时,二阶PMD的影响可以忽略;但当其值增大时,输出信号劣化严重.在光纤通信系统设计时,需要考虑偏振模色散影响分析结果,可提供参考依据.     

偏振模色散模拟器一阶及二阶偏振模色散统计特性的分析

从光纤的琼斯矩阵模型出发,利用蒙特-卡洛方法对偏振模色散模拟器的统计特性进行了研究.研究结果表明:随着组成模拟器的保偏光纤的段数增加,一阶和二阶偏振模色散的统计分布越接近于理论拟合曲线.比较了两种不同模拟器的组成方法,得到的结果将对模拟器的设计具有实际的指导作用.     

Spin waves on chains of YIG particles: dispersion relations,Faraday rotation,and power transmission

We calculate the dispersion relations for spin waves on a periodic chain of spherical or cylindrical Yttrium Iron Garnet (YIG) particles. We use the quasistatic approximation, appropriate when kd ? 1, where k is the wave number and d the interparticle spacing. In this regime, because of the magnetic dipole-dipole interaction between the localized magnetic excitations on neighboring particles, dispersive spin waves can propagate along the chain. The waves are analogous to plasmonic waves generated by electric dipole-dipole interactions between plasmons on neighboring metallic particles. The spin waves can be longitudinal (L), transverse (T), or elliptically polarized. We find that a linearly polarized spin wave undergoes a Faraday rotation as it propagates along the chain. The amount of Faraday rotation can be tuned by varying the off-diagonal component of the permeability tensor. We also discuss the possibility of wireless power transmission along the chain using these coupled spin waves.