Discrete negative refraction in photonic crystal waveguide arrays

We report a systematic analysis of anomalous refractive effects at interfaces between two photonic crystal waveguide arrays. Discrete negative refraction can be easily predicted from the sign of the coupling coefficient between adjacent waveguides, regardless of handedness of propagation.     

Nonlinear optical beam interactions in waveguide arrays

We report our investigation of Kerr nonlinear beam interactions in discrete systems. The influence of power and the relative phase between two Gaussian shaped beams was investigated in detail by performing numerical simulations of the discrete nonlinear Schr?dinger equation and comparing the results with experiments done in AlGaAs waveguide arrays. Good agreement between theory and experiment was obtained.     

Low loss dielectric optical waveguide bends

The pure bend loss of a curved dielectric optical waveguide can be reduced effectively with only a slight change in the transverse field distribution by replacing the cladding material outside the caustic by another material with a smaller refractive index. This is demonstrated by microwave model experiments.     

Low loss dielectric optical waveguide bends

The pure bend loss of a curved dielectric optical waveguide can be reduced effectively with only a slight change in the transverse field distribution by replacing the cladding material outside the caustic by another material with a smaller refractive index. This is demonstrated by microwave model experiments.     

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.     

Unidirectional optical Bloch oscillations in asymmetric waveguide arrays

We present an analytical proof of the existence of unidirectional optical Bloch oscillations in a waveguide array system. It is shown that the presence of nonreciprocity in the system allows for a complete normal-mode dephasing in one of the propagation directions, resulting in a unidirectional breakdown in Bloch oscillations. A model system consisting of an array of transversely magnetized asymmetric Si/SiO2 waveguides with a magneto-optic cover layer is presented. Large index contrasts between film and cover are critical for practical realizations.     

Surface optical Bloch oscillations in semi-infinite waveguide arrays

We predict that surface optical Bloch oscillations can exist in semi-infinite waveguide arrays with a linear index variation, if the array parameters close to the boundary are appropriately perturbed. The perturbation is such that the surface states obtain the Wannier-Stark ladder eigenvalues of the unperturbed infinite array. The number of waveguides, whose parameters need to be controlled, decreases with increasing ratio of index gradient over coupling. The configuration can find applications as a "matched" termination of waveguide arrays to eliminate the distortion of Bloch oscillations due to reflection on the boundaries.     

Nonlinear band gap transmission in optical waveguide arrays

The effect of nonlinear transmission in coupled optical waveguide arrays is theoretically investigated and a realistic experimental setup is suggested. The beam is injected in a single boundary waveguide, linear refractive index of which (n(0)) is larger than refractive indexes (n) of other identical waveguides in the array. Particularly, the effect holds if omega(n(0)-n)/c>2Q, where Q is a linear coupling constant between array waveguides, omega is a carrier wave frequency, and c is a light velocity. Numerical experiments show that the energy transfers from the boundary waveguide to the waveguide array above a certain threshold intensity of the injected beam. This effect is due to the creation and the propagation of gap solitons in full analogy with a similar phenomenon in sine-Gordon lattice [Phys. Rev. Lett. 89, 134102 (2002)]].     

Amplifying optical signals with discrete solitons in waveguide arrays

We present a design and protocol to achieve an essential feature of an optical transistor, namely the amplification of input signal with the use of discrete solitons in waveguide arrays. We consider the scattering of a discrete soliton by a reflectionless potential in the presence of a control soliton. We show that at the sharp transition region between full reflectance and full transmittance, the intensity of the reflected or transmitted soliton is highly sensitive to the intensity of the control soliton. This suggests a setup of signal amplifier. For realistic purposes, we modulate the parameters of the reflectionless potential well to achieve a performance of amplifier with a controllable amplification. To facilitate the experimental realization, we calculate the amplification factor in terms of the parameters of the potential well and the input power of the control soliton. The suggested signal amplifier device will be an important component in the all-optical data processing.     

The peculiarities of discrete diffraction in two-dimensional optical waveguide arrays

The fundamental peculiarities of discrete diffraction in the two-dimensional waveguide arrays were studied. The discrete diffraction properties of such arrays can be effectively altered, depending upon the input conditions. By slightly changing the input conditions, light can experience normal diffraction in one-direction and experience anomalous diffraction in the other.     

Three-mode coupling in a passive dielectric waveguide with index modulation

The characteristics of a three-mode coupling in a passive dielectric waveguide are investigated for the case of even TE modes. The index is assumed to have a doubly periodic harmonic variation in the propagation direction. By a singular perturbation procedure using multiple space scales, the coupled-mode equations governing the Bragg interactions are systematically deduced. The three-mode coupling causes a stop band in frequency and the characteristics of the resulting evanescent mode are analyzed. For a periodic dielectric waveguide of finite length, the three coupled-mode equations are solved subject to suitable boundary conditions to obtain the reflection and the transmission coefficients. The frequency response of the reflection and the transmission coefficients are investigated and compared with the results of the pair of corresponding two-mode couplings. Representative numerical results are presented to illustrate the characteristics of the interaction of the three modes.     

梯形截面介质光波导的模吸收损耗

本文运用微分法由梯形截面介质光波导的近似模方程导出了模吸收损耗系数的公式.并结合计算实例进行了误差分析.     

Dual resonance mechanisms facilitating enhanced optical transmission in coaxial waveguide arrays

We experimentally and computationally demonstrate high transmission through arrays of coaxial apertures with different geometries and arrangements in silver films. By studying both periodic and random arrangements of apertures, we were able to isolate transmission enhancement phenomena owing to surface plasmon effects from those owing to the excitation of cylindrical surface plasmons within the apertures themselves.     

Hybrid waveguide-plasmon resonances in gold pillar arrays on top of a dielectric waveguide

We propose a hybrid waveguide-plasmon system consisting of gold pillar arrays on top of a dielectric waveguide. The formation of extraordinary transmissions induced by the hybrid waveguide-plasmon resonances is investigated by rigorous coupled-wave analysis. The characteristics of the hybrid resonances can be predicted by introducing the photonic crystal slab theory. Extremely narrow absorption peaks and the electromagnetically induced transparency-like optical property are demonstrated in our hybrid system.     

Rigorous analysis of optical forces between two dielectric planar waveguides immersed in dielectric fluid media

This work presents a rigorous analysis of optical forces between planar waveguides immersed in an arbitrary background medium. This approach exploits the Minkowski stress tensor formulation, which is compared with a normalized version of the dispersion relation method, showing excellent results agreement for different dielectric fluid media. Due to slot‐waveguide effect, optical forces from TM modes are more sensitive to changes in the fluid refractive index than the TE counterparts. Furthermore, the repulsive optical force from the antisymmetric TM1 mode becomes stronger for higher refractive indexes, whereas the attractive force of the symmetric TM0 mode becomes weaker. The methodology and results presented in this work provide a rigorous analysis of nano‐optomechanical devices actuated by optical forces in a broad range of materials and applications. Therefore, this study may impact areas of light‐induced interactions presenting novel optofluidic and optomechanical functionalities, thus finding applications in nanoscale transport, sensing and manipulation.

     

Unidirectional flow of discrete solitons in optical waveguide arrays with nonlinearity management

We propose a mechanism for realising a unidirectional flow of discrete solitons in optical waveguide arrays. Modulating the nonlinear interaction strength in each waveguide according to a double reflectionless potential well with slight difference in the depths of its two wells, we achieve a unidirectional flow of the soliton propagation. We verify clearly, through the transport coefficients as in terms of the speed of the incident soliton, that an incident soliton velocity window of finite width exists where unidirectional flow can be realised. We discuss the physics underlying this behaviour on the basis of energy exchange between the soliton's kinetic and interaction energies.     

光波段多频负折射率超材料

从光波段圆孔形双鱼网结构的负折射材料模型出发,采用基于有限积分技术的CST软件系统研究了原胞结构的改变对负折射行为的影响.数值仿真结果表明,对原胞结构做微小调节也可获得负折射率频带的增大效应.将双鱼网结构改为阶梯形孔洞和半球形孔洞结构,可以在更多的频段里出现负折射率,并且谐振频率发生了一定的红移.半球形孔洞的双鱼网结构可以方便地用化学模板法制备,这为从实验上实现红外及可见光波段的多频负折射材料提供了一种简单可行的方法. 关键词： 负折射率 多频段 双鱼网结构     

Nonadiabatic Landau-Zener tunneling in waveguide arrays with a step in the refractive index

Landau-Zener tunneling is discussed in connection with optical waveguide arrays. Light injected in a specific band of the Bloch spectrum in the propagation constant can be transmitted to another band, changing its physical properties. This can be achieved using two coupled waveguide arrays with different refractive indices. The step in the refractive index causes wave "acceleration" and thus induces strongly nonadiabatic Landau-Zener tunneling. Theoretically, the analysis is performed by considering a Schr?dinger equation in a periodic potential with a step. The region of physical parameters where this phenomenon can occur is analytically determined and a realistic experimental setup is suggested. Its application could allow the realization of light filters.     

Field enhancement of gold optical nanoantennas mounted on a dielectric waveguide

In this paper, we investigate the localized field enhancement of optical nanoantennas consisting of different types of coupled gold nanoparticles and fed by a silicon nitrite slab waveguide. The optical nanoantenna is mounted on the surface of the waveguide, and the incident blue-violet light is guided in the slab waveguide and then reflected to the nanoatenna at the end of the waveguide. We also study the performance of the slab waveguide with different optimized parameters and also the field enhancement achieved by different shapes of nanoantennas.     

Coexistence of Josephson oscillations and a novel self-trapping regime in optical waveguide arrays

Considering the coherent nonlinear dynamics between two weakly linked optical waveguide arrays, we find the first example of coexistence of Josephson oscillations with a novel self-trapping regime. This macroscopic bistability is explained by proving analytically the simultaneous existence of symmetric, antisymmetric, and asymmetric stationary solutions of the associated nonlinear Schr?dinger equation. The effect is illustrated and confirmed by numerical simulations. This property allows us to conceive an optical switch based on the variation of the refractive index of the linking central waveguide.