保偏光纤陀螺轴向磁敏感特性研究

研究了与光纤线圈敏感轴平行的轴向磁场作用下保偏光纤陀螺的漂移特性,建立了保偏光纤陀螺产生的非互易相位差与入射光偏振态关系的数学模型,并对该模型进行了实验验证.结果表明:轴向磁场对保偏光纤陀螺产生的非互易相位差源于光纤线圈内光纤的弯曲,且与线圈中光纤扭转分布具有密切关系,即当线圈绕制完毕,光纤扭转分布固定时,对应的保偏光纤陀螺轴向磁场灵敏度不变;保偏光纤陀螺轴向磁场灵敏度与射入光纤线圈内光的偏振态密切相关,通过改变入射偏振光的入射角,可在0~5°/h/mT范围内改变典型保偏光纤陀螺的轴向磁场灵敏度.     

保偏光纤干涉型陀螺的磁场误差分析与抑制方法

基于保偏光纤的琼斯矩阵,建立了保偏光纤线圈的Faraday非互易相移模型,利用该模型进行计算发现:线圈保偏光纤的慢轴与快轴的Faraday非互易相移大小近似相等,但符号相反。并进一步提出了偏振环行干涉型保偏光纤陀螺(PCPM-IFOG),它能使顺时针(CW)和逆时针(CCW)光在保偏光纤线圈中沿慢和快轴分别传输一次,因此顺时针和逆时针光总的Faraday非互易相移等于0,实现了Faraday非互易相移的完全抑制。500m保偏光纤线圈的偏振环行干涉型保偏光纤陀螺的实验结果显示其输出与地球磁场无关,而对于相同传感线圈的干涉型保偏光纤陀螺,当磁场方角发生变化时,陀螺有约±0.3°/h的Faraday零偏漂移。     

异面腔四频差动激光陀螺的色散平衡

为了减小异面腔四频差动激光陀螺(DLG)腔长变动导致的零漂,对DLG的色散平衡进行了研究.利用气体激光的经典理论,推导了DLG零偏与工作点和轴向磁场的函数关系,给出了色散平衡的理论证明.利用在DLG增益管上缠绕通电线圈,给增益介质施加大小可控的轴向磁场,通过驱动腔平移镜上的压电换能器调节腔长来改变工作点,做出了零偏随腔长和线圈电流的变化曲线.结果表明,零偏对腔长变化的灵敏度是轴向磁场的函数,当增益曲线的塞曼分裂量等于非互易分裂量时零偏对腔长变动不敏感.色散平衡技术减小了腔变动对DLG的影响,有利于提高DLG精度.     

磁场对四频差动激光陀螺光强和零偏的影响

研究了四频差动激光陀螺输出光强和零偏随纵向磁场的变化规律。理论分析表明,当由纵向磁场引起的增益/色散曲线的塞曼分裂等于非互易分裂时,顺时针模式和逆时针模式的光强相等,零偏不随腔长的变化而变化,实验结果与理论分析基本一致。同时还发现顺时针和逆时针模式的光强随磁场线性变化,但变化量较小且易受温度的影响,不适合作为磁场大小的度量。由于沿谐振腔环路的增益和损耗并非处处相同,顺时针和逆时针光束入射到光电管上的量不相等,因此需要对顺时针和逆时针输出光强的放大倍数进行标定,以便进行色散平衡的控制。     

层流平衡相对论电子束束流特性的数值计算

通过对层流平衡相对论电子的运动微分方程组进行数值求解,得到正则角动量在pθ=0,pθ=const.和pθ∝r2三种情况下,束流的传输特性.针对pθ=0的相对论实心电子束,利用数值求解得到了与解析方法一致的结果,从而验证了数值方法的合理性;针对无法用解析方法求解的pθ=0环行电子束、pθ=const.和pθ∝r2的情况,利用数值方法得到了束流和空间极限电流关于波导、电子束结构和二极管电压等参数的变化规律及对轴向导引磁场的要求.计算结果表明:当相对论电子束以层流平衡态传输时,环行束较实心束具有更高的空间极限电流和更低的轴向导引磁场,且当阴极发射面与导引磁场的磁场线垂直时,维持电子束层流平衡所需的轴向导引磁场最低;电子束在有限磁场导引下以层流平衡态传输时,空间极限电流明显大于无限大磁场导引下一维近似的情况.利用数值方法对层流平衡相对论电子束进行理论研究,更全面地揭示了电子束在正则角动量满足不同条件时的束流特性,为设计新型结构的高功率微波器件提供理论参考.     

双光程光纤陀螺的温度致非互易性研究(英文)

为了提高陀螺的精度,提出了一种新型双光程光纤陀螺.在光纤环两端各连接一个偏振分束器,使得偏振光依次沿保偏光纤的快轴、慢轴传输两圈,其有效光程加倍,进而实现陀螺的Sagnac效应加倍.针对该光纤陀螺在温度场扰动下的非互易问题,分析了其特殊结构带来的温度致非互易误差,利用有限元分析法建立了相应的Shupe误差模型,并对光纤环90°熔点位置、光纤环折射率温度系数改变对Shupe误差影响进行了相应的理论计算与仿真分析,结果表明90°熔点置于光纤环中点或者选用折射率温度系数满足特定条件的光纤环可减小其Shupe误差.     

Duffing振子型结构声系统中声能量非互易传递的建模和实验研究

声能量非互易传递机理及声非互易系统构建是近年来声学领域的研究热点.本文开展了由非线性薄膜和两个不同尺寸声腔组成的实验系统中声能量非互易传递的实验研究.该系统利用简化为Duffing振子的薄膜频响函数的不对称性,实现了声能量的非互易传递.采用复化平均法获得系统频响函数的渐近解,理论计算结果与实验测量结果吻合.理论计算和实验结果表明:该系统理论上存在最大9.1倍的非互易量,实验测得的最大非互易量为4.3倍,归一化跳变区频率带宽为0.56.研究结果揭示了实验系统中声能量非互易传递机理,为实现空气介质声系统中声能量的非对称传递提供了一种新方法.     

一维磁化等离子体光子晶体非互易特性研究

在理想条件下,为了研究等离子体回旋频率、等离子体频率、等离子体层厚度、周期常数和入射角在TM模式下对一维磁化等离子体光子晶体的非互易特性的影响,用利用传输矩阵法计算得到的TM波正向和反向传播的透射率来研究其非互易特性。研究结果表明,增加等离子体回旋频率和入射角度能够改善非互易特性;而一味地增加等离子体频率和等离子体层厚度将会使得非互易传播特性变得恶化;增加周期常数不能明显地改善非互易传播特性,但是通过改变外加磁场的施加方式能够改善其非互易特性。     

循环频移方法中射频信号的相位偏移对多载波稳定性及平坦度的影响(英文)

为了得到高性能的多载波光源,研究了射频信号中不同相位差对光多载波的影响.通过理论分析可得,随着相位差从90°降至0°,光多载波性能会逐渐变差,但是相位差偏与90°相差不大时,性能不会下降太多.实验中通过移相器改变相位差,使相位差为90°,45°,0°,得到循环前IQ调制器的输出光谱,并对比循环后光多载波性能.实验结果显示,相位差为90°时,循环前IQ调制器输出为较好的单边带光谱,循环后输出50条平坦稳定光多载波;相位差为45°时,光多载波质量变差;相位差为0°时,得不到光多载波.因此,射频信号相位差为90°时,光多载波的性能最佳,随着相位差变小,性能下降,但是相位差为45°时,产生的光多载波仍可应用于光通信.     

等离子体金属波导在外磁场调制下的传输模式

在通信系统中波导的设计向着多功能和可调制方向发展。波导基于等离子体金属材料在外磁场作用下设计平面波导。等离子体金属材料在外磁场作用下会产生表面等离子体激元和非互易传播双重功能。从基本的麦克斯韦方程和边界条件出发,详细推导了模式的色散方程,并根据模式特征进行了分类。波导具有明显的非互易传播和可调制的特性。     

Optical isolator based on nonreciprocal coupling of two Tamm plasmon polaritons

In this paper, we have studied the one-dimensional photonic crystal (PC) including a magneto-optical metal defect using the developed transfer matrix method for magnetic materials. Around the two interfaces between metal and one-dimensional PC, two nonsymmetric Tamm magneto-plasmon polaritons may be excited and coupled. The coupled states take on a clear nonreciprocal behavior and result in nonreciprocal transmission. The results are demonstrated through electromagnetic field distribution simulations based on finite element software. It provides a useful reference to realize optical isolator design.     

FeRh合金顺磁到铁磁相变的对称理论

应用第二类相变的对称理论于磁性体系,导出了不同于幺正群情形的共表示的Molien函数;讨论了FeRh合金的对称破缺方向;发现由于磁群的共表示非磁群的真正同态,共表示意义下的等价不可约表示可导致不同的对称破缺;存在O_h¹⊕θO_h¹→C_4v¹⊕θ[D_4h¹-C_4v¹]的连续磁相变,与实验结果一 关键词：     

Modeling and simulation of polarization errors in Sagnac fiber optic current sensor

Sagnac fiber optic current sensor (S-FOCS) is a kind of optical interferometer based on Sagnac structure, optical polarization states of sensing light wave in Sagnac fiber optic current sensor are limited. However, several factors induce optical polarization error, and non-ideal polarized light waves cause the interference signal crosstalk in sensor, including polarizer, quarter-wave retarder, splice angular, birefringence and so on. With these errors, linearly polarized light wave in PM fiber and circularly polarized light wave in sensing fiber become elliptically polarized light wave, then, nonreciprocal phase shift induced by magnetic field of the current is interrupted by wrong polarization state. To clarify characteristics of optical polarization error in fiber optic current sensor, we analyze the evolution process of random optical polarization state, linear optical polarization state and circular optical polarization state in Sagnac fiber optic current sensor by using Poincare sphere, then, build optical polarization error models by using Jones matrix. Based on models of polarization state in Sagnac fiber optic current sensor, we investigate the influence of several main error factors on optical polarization error characteristics theoretically, including extinction ratio in polarizer, phase delay in quarter-wave retarder, splice angular between quarter-wave retarder and polarization maintaining fiber. Finally, we simulate and quantify nonreciprocal phase shift to be detected in fiber optic current sensor related with optical polarization errors. In the end, we demonstrate S-FOCS in test. The results show that transfer matrix errors are induced by inaccurate polarization properties during polarization state conversion, then, the stability and accuracy of the S-FOCS are affected, and it is important to control the polarization properties at each step of the polarization state conversion precisely.     

Nonreciprocal microwave transmission under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect

Nonreciprocal microwave devices, in which the transmission of waves is non-symmetric between two ports, are indispensable for the manipulation of information processing and communication. In this work, we show the nonreciprocal microwave transmission in a cavity magnonic system under the joint mechanism of phase modulation and magnon Kerr nonlinearity effect. In contrast to the schemes based on the standard phase modulation or magnon Kerr nonlinearity, we find that the joint mechanism enables the nonreciprocal transmission even at low power and makes us obtain a high nonreciprocal isolation ratio. Moreover, when two microwave modes are coupled to the magnon mode via a different coupling strength, the presented strong nonreciprocal response occurs, and it makes the nonreciprocal transmission manipulating by the magnetic field within a large adjustable range possible, which overcomes narrow operating bandwidths. This study may provide promising opportunities to realize nonreciprocal structures for wave transmission.     

Polarization transformers for optical anisotropy: I. Nonreciprocal optical systems and the equivalence theorem

The problem of transformation of anisotropic properties of multipass nonreciprocal systems is considered. The equivalence theorem is generalized to the case of nonreciprocal elements (i.e., to elements that do not satisfy the equivalence theorem). It is shown that any nonreciprocal anisotropic phase element is equivalent to a combination of five elements, namely, a reciprocal linear phase plate, a nonreciprocal linear phase plate, a reciprocal rotator, and two Faraday rotators. The difference between reciprocal and nonreciprocal elements is considered from the viewpoint of their basis states.     

Nonreciprocal transition between two indirectly coupled energy levels

We propose a theoretical scheme to realize nonreciprocal transition between two energy levels that can not coupled directly. Suppose they are coupled indirectly by two auxiliary levels with a cyclic four-level configuration, and the four transitions in the cyclic configuration are controlled by external fields. The indirectly transition become nonreciprocal when the time reversal symmetry of the system is broken by the synthetic magnetic flux, i.e., the total phase of the external driving fields through the cyclic four-level configuration. The nonreciprocal transition can be identified by the elimination of a spectral line in the spontaneous emission spectrum. Our work introduces a feasible way to observe nonreciprocal transition in a wide range of multi-level systems, including natural atoms or ions with parity symmetry.     

A software-compensation method to orthogonal magnetic field drift in a depolarized fiber-optic gyroscope

An orthogonal magnetic field vertical to the light propagating direction will initiate a nonreciprocal phase drift in a depolarized interferometric fiber-optic gyroscope (D-IFOG). This drift appears a linear correlation to the magnitude of the orthogonal magnetic field. We proposed a software-compensation method by attaching two differential Hall sensors to the D-IFOG to sample the magnetic field in real time and the experimental results showed a notable improvement to the magnetic stability.     

基于图像信息熵的ptychography轴向距离误差校正

在轴向距离参与运算的ptychography算法中,轴向距离误差会使重建图像变模糊并降低图像的分辨率.本文基于菲涅耳衍射理论建立了轴向距离误差模型,根据不同轴向距离误差对重构图像清晰度的影响,提出用图像信息熵确定图像最清晰时的轴向距离,并重建出清晰的ptychography图像.比较了图像能量变化、Tamura系数和图像信息熵这三种图像清晰度评价函数在轴向距离误差校正过程中的分布情况,发现它们均具有单峰性,且峰值确定的轴向距离相同.图像信息熵相比其他两种图像清晰度评价函数具有更高的灵敏性.仿真以及实验均证明了基于图像信息熵的ptychography轴向误差校正的可行性.