固体激光器与光纤激光器对光子晶体光纤棒耦合的分析与对比

耦合效率的高低与耦合后光斑的好坏直接影响着光子晶体光纤棒的放大效果,因此需要对种子光的耦合效果进行研究,选择合适的激光器作为种子源。本文对光子晶体光纤棒在固体激光器与光纤激光器两种情况下的耦合效率进行了理论分析;模拟计算了两种激光器情况下耦合效率的变化规律以及对准误差对耦合效率的影响;选择合适的透镜或透镜组,使用两种激光器对光子晶体光纤棒进行了耦合实验;对比两种激光器的耦合效果可知:固体激光器的耦合效率最高只能达到62.4%,而光纤激光器的耦合效率可以达到80%以上;在光纤激光器耦合情况下,对不同功率注入时耦合效率,以及耦合后光斑进行了实验分析。得到的实验结果对后续光纤棒的放大实验具有指导作用。     

Variational determination of the stringtension and the glueball mass in (2+1) dimensionalU (1) lattice gauge theory for all values of the coupling constant

Using variational ansätze of the product type we calculate the massgap and the stringtension of (2+1) dimensionalU(1) lattice gauge theory in the Hamiltonian formalism for all values of the coupling constant. In the strong coupling limit our results agree with high order strong coupling series. In the weak coupling limit both, glueball mass and stringtension vanish exponentially with the coupling constant.     

信噪比对偏振耦合测试影响分析

以白光麦克尔逊干涉仪对双折射保偏光纤的偏振耦合进行测试,并基于仪器结构建立了测试扫描结果的数学模型.分析及仿真了信噪比对耦合强度及耦合位置检测的影响大小及变化趋势.信噪比大于32dB,可满足偏振耦合测试的要求.     

耦合摆特性模拟及振动耦合现象演示

分析了机械耦合摆的振动特性及耦合过程,提出了利用互感耦合电路模拟耦合摆的方法;设计并制作了—种互感耦合装置,模拟机械耦合摆的振动耦合和能量转换过程;通过与机械耦合的比对演示,将两种耦合的特性分析归结为相同的数学问题,在演示物理现象的同时,培养学生数学建模能力和对系统的综合分析能力.     

On the optimization of the effective electromechanical coupling coefficients of a piezoelectric body

Effective electromechanical coupling coefficients are defined based on the expression for the internal energy of a piezoelectric body [B. S. Aronov, "Energy analysis of a piezoelectric body under nonuniform deformation," J. Acoust. Soc. Am. 113, 2638-2646 (2003)]. The condition is considered under which the effective coupling coefficient can be maximized up to the value of the material coupling coefficient for any given distribution of deformation. A simple practical way to optimize the effective coupling coefficient of a transducer by changing its electrode shape is illustrated with examples of transducers vibrating in longitudinal and flexural modes.     

利用二维光子晶体提高波的耦合效率

通过多重散射方法数值模拟研究和实验测量表明利用二维光子晶体可以提高波的耦合效率.研究发现,高的波耦合效率通常发生在光子禁带的边沿和其它非禁带区的某些频率处.当光子晶体的晶格常数接近于所传输的波的波长时,会出现很高耦合效率的共振耦合现象.利用二维光子晶体的情况下的波耦合效率最高可以达到不利用二维光子晶体时的1.89倍.这种现象在光集成器件中尤其有用.     

精确计算非旋波近似下二能级系统的能谱和动力学性质

利用相干态正交化展开法,精确求解了非旋波近似下Jaynes-Cummings模型的能谱和动力学性质.与近似下解析解比较发现,在弱耦合和强耦合区近似解析解与数值精确解符合很好,但在中间耦合区符合较差. 关键词： 相干态正交化展开 非旋波近似 Jaynes-Cummings模型     

钾扩散耦合引起的心脏中螺旋波的变化

在某些情况下, 心肌细胞外的钾离子浓度是变化的, 钾离子的横向扩散会导致细胞外钾离子的聚集和产生钾扩散耦合, 用考虑钾扩散耦合的Luo-Rudy相I心脏模型研究了钾扩散耦合对螺旋波动力学的影响. 数值模拟结果表明: 当钾扩散耦合比较强时, 钾扩散耦合使细胞外钾离子浓度先升高, 然后做规则振荡, 导致螺旋波做无规则漫游; 观察到螺旋波的波臂宽度和频率随钾扩散耦合的强度增大而减小, 这样, 当钾扩散耦合足够强时, 钾扩散耦合可以消除螺旋波和时空混沌. 关键词： 钾扩散耦合 螺旋波 时空混沌     

一种实现光纤耦合器分光比微调的新方法

随着光纤通信技术的不断发展,光纤通信中至关重要的光无源器件——光纤耦合器,其使用量正在不断的增加。如何提高光纤耦合器的成品率已成为一个很重要的问题。通过对具有一定分光比的未封装的窄带光纤耦合器的一端进行固定和在另一端进行扭转,可以实现耦合器分光比的微调。实验表明,对耦合器施加扭转力矩会使耦合器的分光比发生一定的变化,并且在扭转的过程中附加损耗的变动很小。利用这一特性可以对偏离预定分光比的耦合器的分光比实现微调,从而可得到更符合要求的分光比,提高了成品率。     

The impact of the off-axis for the spatial light to multimode fiber coupling system

The electric field distribution of Gaussian beam and properties of Cassegrain optical antenna are discussed and their images have been simulated. By analysis of Cassegrain optical antenna with collimation and off-axis circumstance, laser power distribution and the curve of coupling efficiency are obtained. The question of spatial light to multimode fiber coupling efficiency with alignment and off-axis are researched. At last, taking into account off-axis situation of Cassegrain and laser beam to multimode fiber, the coupling efficiency of the whole system is discussed. These researches are necessary and useful for increasing spatial light to multimode fiber coupling efficiency.     

Study of magnetoelectric coupling effect in the hexagonal ferroelectromagnet

Soft-mode theory based on Diffour model for ferroelectric subsystem, and mean-field theory as well as Heisenberg model for antiferromagnetic subsystem are utilized to investigate the magnetoelectric coupling effect in a hexagonal ferroelectromagnet, in which the ferroelectric and antiferromagnetic orders spontaneously coexist below a certain temperature. An anomaly of polarization at the magnetic transition temperature is ascribed to the effect of magnetoelectric coupling. The magnetic excitation has also been studied by spin-wave theory over the three-sublattice model. It is demonstrated that role of magnetoelectric coupling effect is not only related with the strength of magnetoelectric coupling but also special spin lattice structure. Our results show the magnetic specific heat induced by magnetic excitation experiences a suppression by the magnetoelectric coupling.     

交换偏置双层膜中的反铁磁自旋结构及其交换各向异性

研究了交换偏置双层膜中界面存在二次以及双二次交换耦合下反铁磁磁矩转动及其交换各向异性.结果表明，其反铁磁膜中的磁矩转动存在可逆“恢复行为”、不可逆“半转动行为”、不可逆“倒转行为”以及不可逆“半倒转行为”四种情形，四种情形的出现强烈地依赖于界面二次、双二次耦合以及反铁磁膜厚度.其中可逆恢复行为情况下，系统出现交换偏置，而不可逆的半转、半倒转以及倒转情形，系统不出现交换偏置.特别地,在界面处仅存在双二次耦合的情形下，其界面双二次耦合常数J₂≤0.1 σ关键词： 反铁磁自旋结构 交换各向异性 界面双二次耦合 交换偏置     

On the coupling of the giant multipole resonances to the surface quadrupole oscillations of nuclei

Within the framework of the hydrodynamic model the exact coupling constants of the coupling of the giant multipole resonances to the surface quadrupole oscillations of nuclei are derived. The differences to former variational calculations are discussed. It is found that the coupling constants for the terms linear in the surface variables are almost the same whereas the coupling constants for the quadratic terms differ appreciably. The influence on the photon absorption and scattering cross sections of spherical nuclei is discussed.     

Development and transition of spiral wave in the coupled Hindmarsh--Rose neurons in two-dimensional space

The dynamics and the transition of spiral waves in the coupled Hindmarsh--Rose (H--R) neurons in two-dimensional space are investigated in the paper. It is found that the spiral wave can be induced and developed in the coupled HR neurons in two-dimensional space, with appropriate initial values and a parameter region given. However, the spiral wave could encounter instability when the intensity of the external current reaches a threshold value of 1.945. The transition of spiral wave is found to be affected by coupling intensity D and bifurcation parameter r. The spiral wave becomes sparse as the coupling intensity increases, while the spiral wave is eliminated and the whole neuronal system becomes homogeneous as the bifurcation parameter increases to a certain threshold value. Then the coupling action of the four sub-adjacent neurons, which is described by coupling coefficient D’, is also considered, and it is found that the spiral wave begins to breakup due to the introduced coupling action from the sub-adjacent neurons (or sites) and together with the coupling action of the nearest-neighbour neurons, which is described by the coupling intensity D.     

Quantum dynamics of interacting modes in the process of intracavity subharmonic generation

The dynamics of correlation between fluctuations of the number of photons of interacting modes is investigated for the process of intracavity subharmonic generation. It is demonstrated that this correlation strongly depends on the nonlinear mode coupling coefficient. For small values of the coupling coefficient, the correlation between fluctuations of the number of photons is small. With an increase in the coupling coefficient, the correlation increases (the state of subsystems becomes entangled) and, starting from a particular value of the coupling coefficient, starts to decrease with further increase in the coupling coefficient, gradually approaching zero (entanglement of subsystem states decreases). The quantum dynamics of the number of photons, quantum entropy, and Wigner function of the stationary state of the fundamental and subharmonic modes is investigated. It is demonstrated that the dynamics of these quantities also strongly depends on the coupling coefficient of the interacting modes. We show that, for large values of the mode coupling coefficient and long interaction times, the subharmonic mode becomes localized in a two-component state with equal probabilities of finding it in each component. Quantum entropy of this state is smaller than maximum entropy of the two-component state equal to ln2, which suggests that quantum-mechanical interference takes place between the subharmonic mode components.     

The Third Law of Quantum Thermodynamics in the Presence of Anomalous Couplings

The quantum thermodynamic functions of a harmonic oscillator coupled to a heat bath through velocity-dependent coupling are obtained analytically. It is shown that both the free energy and the entropy decay fast with the temperature in relation to that of the usual coupling from. This implies that the velocity-dependent coupling helps to ensure the third law of thermodynamics.     

On the low frequency electromagnetic response of strong coupling superconductors

In this paper we report about penetration depth measurements performed on strong coupling Pb–Bi alloys. The change of penetration depth with temperature is obtained from the frequency shift of a superconducting resonant cavity. The experimental results are compared with the low frequency electromagnetic response kernel calculated from the strong coupling theory and the scaled weak coupling theory respectively. A very good agreement between experiment and strong coupling theory is observed. The fit of the scaled weak coupling theory to the measured change of penetration depth yields values of the superconducting energy gap, which agree with the corresponding results of tunneling measurements.     

激光熔融拉锥型微型光纤耦合器设计

采用聚焦红外激光光束进行熔融加热,针对激光熔融拉锥型光纤耦合器设计了一种熔融区域长度为200 μm的微型光纤耦合器.使用光束传输法对拉锥长度和耦合区域的宽度进行了模拟并与实验结果比较,在1320 μm的拉锥长度和14 μm的耦合宽度处找到了最优化且低损耗的耦合器尺寸配置.     

Stability of the curvature perturbation in dark sectors' mutual interacting models

We consider perturbations in a cosmological model with a small coupling between dark energy and dark matter. We prove that the stability of the curvature perturbation depends on the type of coupling between dark sectors. When the dark energy is of quintessence type, if the coupling is proportional to the dark matter energy density, it will drive the instability in the curvature perturbations; however if the coupling is proportional to the energy density of dark energy, there is room for the stability in the curvature perturbations. When the dark energy is of phantom type, the perturbations are always stable, no matter whether the coupling is proportional to the one or the other energy density.     

耦合孔对微波腔的影响研究

从Maxwell方程出发,将微波腔中的实际微波场按其本征模式展开,进行微波腔的工作特性(如工作频率、场分布等)的研究.在具体处理过程中,根据复杂结构微波腔的具体边界,将微波腔分成规则形状微波腔和非规则(含耦合孔)部分,建立实际微波腔模式同规则形状微波腔模式之间的场耦合方程,从而确定耦合孔对微波腔模式的影响,并对开耦合孔的圆柱腔进行了相应的理论和模拟研究. 关键词： 微波腔 模式 场耦合 圆柱微波腔