Multiple Landau-Zener tunnelling in two weakly coupled waveguide arrays

A visual observation of multiple Landau-Zener transitions between different modes is theoretically proposed by using two weakly coupled waveguide arrays. Applying a small temperature gradient between the opposite corners of the sample it is possible to realize ordinary symmetric Landau-Zener tunnelling exchange between two modes. While increasing the temperature gradient more modes are involved in the tunnelling exchange and the picture becomes asymmetric even in the linear limit. We interpret this phenomenon via dynamics associated with Schr?dinger equation in double well potential and additional gradient potential along both dimensions.     

Plasmonic Zener tunneling in metal-dielectric waveguide arrays

We elucidate in this Letter plasmonic Zener tunneling (PZT) in metal-dielectric waveguide arrays (MDWAs) by using numerical simulations and theoretical analyses. PZT in MDWAs occurs at the waveguide entrance and wherever the beam completes Bloch oscillations, because the bandgap between the first and second bands is minimal at the center of the first Brillouin zone. This feature significantly differs from that of optical Zener tunneling in dielectric waveguide arrays. The dependence of the simulated tunneling rate on the gradient of the relative permittivity of the dielectric layers correlates with the tunneling theory, thus confirming the occurrence of PZT in MDWAs.     

Collective spontaneous emission in a waveguide with a near-zero refractive index

The optimum conditions for observing superradiance and subradiance effects in an ensemble of two-level atoms, placed in a waveguide cladding with a metamaterial with near-zero refractive index, are discussed.     

Asymmetric Landau-Zener tunneling in a periodic potential

Using a simple model for nonlinear Landau-Zener tunneling between two energy bands of a Bose-Einstein condensate in a periodic potential, we find that the tunneling rates for the two directions of tunneling are not the same. Tunneling from the ground state to the excited state is enhanced by the nonlinearity, whereas in the opposite direction it is suppressed. These findings are confirmed by numerical simulations of the condensate dynamics. Measuring the tunneling rates for a condensate of rubidium atoms in an optical lattice, we have found experimental evidence for this asymmetry.     

Spatiotemporal collapse in a nonlinear waveguide with a randomly fluctuating refractive index

Analytical results, based on the virial theorem and the Furutsu-Novikov theorem, of the spatiotemporal evolution of a pulse in a nonlinear waveguide with a randomly fluctuating refractive index are presented. For initial conditions in which total collapse occurs in a homogeneous waveguide, random fluctuations postpone the collapse. Sufficiently large-amplitude and short-wavelength fluctuations can cause an initially localized pulse to spread instead of contracting. We show that the disorder can be applied to induce a high degree of controllability of the spatiotemporal extent of the pulses in the nonlinear waveguide.     

Oscillation of spatial solitons in a waveguide with a symmetrical refractive index profile

Dynamics of (1+1)D spatial solitons in a Kerr medium with a transversely symmetrical refractive index profile is investigated. Propagation of solitons is analysed theoretically by using an effective-particle approach. Analytical results show that the soliton oscillates periodically with a variable acceleration. The expression of oscillatory period is derived by introducing a concept of `average acceleration'. Both acceleration and oscillatory period are determined by the parameters of the input soliton and the waveguide. Propagations of solitons are simulated numerically and good agreement is obtained between the theoretical and numerical results.     

玻色-费米混合气体的非线性Landau-Zener隧穿

在有相互作用的非线性两模系统中, 通过对相互作用参数的调节, 研究了该系统中玻色-费米混合气体的Landau-Zener隧穿现象. 研究发现, 其中某一组分的自相互作用会影响另一组分粒子的隧穿, 使得隧穿出现临界现象. 关键词： 玻色-费米混合气体 Landau-Zener隧穿 量子绝热隧穿     

Atomic Landau-Zener tunneling in Fourier-synthesized optical lattices

We report on an experimental study of quantum transport of atoms in variable periodic optical potentials. The band structure of both ratchet-type asymmetric and symmetric lattice potentials is explored. The variable atom potential is realized by superimposing a conventional standing wave potential of lambda/2 spatial periodicity with a fourth-order multiphoton potential of lambda/4 periodicity. We find that the Landau-Zener tunneling rate between the first and the second excited Bloch band depends critically on the relative phase between the two spatial lattice harmonics.     

二维周期光子晶格中的非线性Landau-Zener隧穿

在二维周期光子晶格中研究了Kerr型非线性Landau-Zener隧穿. 首先在六方晶系光子晶格中推导出非线性三能级Landau-Zener隧穿模型, 在特殊初值条件下将其转化为非线性二能级模型. 对于三能级隧穿模型, 选择特殊初值, 研究了隧穿率随参数的变化规律. 关键词： 光子晶格 Kerr型非线性 Landau-Zener隧穿     

Slow light in a dielectric slab waveguide with a negative refractive index photonic crystal substrate

Slow light effect in a dielectric slab waveguide with a negative refractive index photonic crystal substrate is numerically investigated. The guided modes are confined in the core layer by total internal reflection. Dispersion and wave propagating properties are explored in details. The result demonstrates that light speed can approach zero at two adjacent frequencies, which is also verified by finite-difference time-domain (FDTD) simulation. Calculated Q-factors both exceed several thousand. The structure has the potential to be used as high-Q open cavity for dual-wavelength lasers or traveling wave amplifiers.     

Landau-Zener tunneling of Bose-Fermi mixture in double-well

The nonlinear Landau-Zener tunneling of a Bose-Fermi mixture in a double-well potential is studied in the present paper. The effect of interaction parameters on bosonic and fermionic tunneling probability is studied for the mixture of ⁴⁰K-⁸⁷Rb. The tunneling phenomena of the system can be controled by adjusting sweeping rate, intraspecies interaction, interspecies interaction and the numbers of bosons and fermions. It is noted that there are three different regions in phase diagram: self-trapping (ST), complete tunneling (CT) and incomplete tunneling (ICT).     

Oscillatory behavior of spatial soliton in a gradient refractive index waveguide with nonlocal nonlinearity

Oscillatory behavior of spatial solitons in a transverse parabolic gradient refractive index distribution (GRIN) waveguide with both local and nonlocal nonlinearity is investigated. Dynamics of such solitons are analyzed by the effective-particle approach method. For weak nonlocal nonlinearity, solitons oscillate in transverse direction periodically during propagation. The normalized width and maximum of refractive index variation of the waveguide play a key role in determining the oscillating period while the position of soliton oscillatory center is slightly influenced by the nonlocal nonlinearity. Stronger nonlocal nonlinearity leads to instability of the oscillatory solitons. Furthermore, the dynamics of the solitons are simulated numerically and good agreements are obtained between the analysis and numerical results. This behavior may be used in all-optical routers, switches etc. PACS 42.65.Tg; 42.65.Jx; 42.65.Wi     

阶变折射率轴棱锥产生局域空心光束

提出利用折射率成阶跃性变化的轴棱锥产生局域空心光束(bottlebeam).讨论了折射率沿径向成阶跃式减小或增加两种模型,从几何光学角度分析了它们产生bottle beam的原理,利用衍射积分理论数值模拟两种轴棱锥光传输的光场分布和不同距离处的二维光斑图,研究结果表明折射率沿径向阶跃减小的轴棱锥产生单个bottle beam,而折射率沿径向阶跃增加的轴棱锥产生具有周期再现的bottle beams.bottle beam在原子引导和囚禁、光学俘获及光镊等方面有广泛的应用,因此本文的研究对bottlebeam的产生和实际应用具有指导意义.     

High refractive index sensitivity sensing in gold nanoslit arrays

The extraordinary optical transmission(EOT) phenomenon of nano-periodic aperture array in metallic film has been widely investigated and used in biosensors. The surface plasmon resonance and cavity mode in some periodic nanostructures, such as nanohole and nanoslit, cause EOTs at certain wavelengths. This resonance wavelength is sensitive to the refractive index on the surface of periodic nanostructures. Therefore, the metallic nanostructures are expected to be good sensing elements. The sensing performances of gold nanoslit arrays are experimentally and theoretically investigated.Three-dimensional finite difference time domain(FDTD) simulations are utilized to explore their transmission spectra and steady-state field intensity distributions. The electron beam evaporation, electron beam lithography, and ion milling are applied to the gold nanoslit arrays with different widths and periods. The sensing performances of the gold nanoslit array are characterized via transmission spectra in four kinds of refractive index samples. The highest sensitivity reaches726 nm/RIU when the width of the gold nanoslit array is 38.5 nm.     

Reverse optical forces in negative index dielectric waveguide arrays

Nonconservative optical forces acting on dipolar particles are considered in longitudinally invariant optical fields. We demonstrate that the orientation of these forces is strictly dictated by the propagation vector associated with such field configurations. As a direct consequence of this, it is impossible to achieve a reversal of optical forces in homogeneous media. We show instead that translation invariant optical tractor fields can in fact be generated in the negative index environment produced in a special class of fully dielectric waveguide arrays.     

Inhibition of light tunneling in chirped and longitudinally modulated semi-infinite waveguide arrays

The inhibition of light tunneling in chirped and longitudinally modulated semi-infinite waveguide arrays where the refractive index is linearly modulated in the transverse direction and harmonically modulated along the light propagation direction is considered. We report on the effect of the refractive index transverse amplitude modulation rate, longitudinal modulation frequency and depth on tunneling inhibition in both linear and nonlinear regimes. We show that in the linear regime an optimal value for the transverse amplitude modulation rate of refractive index exists and can determine the optimal longitudinal modulation frequency or depth leading to a maximum of distance-averaged power fraction. In the nonlinear regime the tunneling inhibition dynamics is affected dramatically by the transverse amplitude modulation rate and the associated electric field amplitude of the input beam.     

双色光晶格势阱中玻色-爱因斯坦凝聚体的Landau-Zener隧穿行为

考虑玻色-爱因斯坦凝聚体局限于周期性的双色光晶格势阱中,研究其中的Bloch能带结构、第一能隙和第二能隙的Landau-Zener隧穿行为.结果表明,随着双色光晶格势阱的主、次晶格相位差从0增加到π,Bloch能带中第一能隙宽度逐渐增加,而第二能隙宽度逐渐减小.同时发现,双色光晶格势阱的主、次晶格深度及其相位差对第一能隙和第二能隙的Landau-Zener隧穿性质有重要的影响.     

Resonant tunneling of a wave through a structure that contains a layer with a negative refractive index

We have investigated the transmission ability of a layered structure the central layer of which is made of a “left-handed” material (its refractive index is negative) and is separated by two air slabs from a “right-handed” dielectric medium that surrounds the structure. We consider tunneling of energy fluxes through the structure and determine conditions for the complete (reflectionless) transmission of the power of the incident wave through it. We show that this effect is resonant and is observed when the tangential component of the wave vector of the incident wave coincides with the longitudinal wave vector of one of waveguiding eigenmodes of the left-handed layer.