左手介质矩形波导导模和表面模的场分布

从麦克斯韦方程组出发,结合电磁场的边界条件,推导出介质矩形波导导模的一般色散方程.对普通介质矩形波导和左手介质矩形波导的导模场分布分别进行了数值模拟.通过对比两种介质矩形波导的导模场分布的模拟结果,发现左手介质矩形波导Ex22模的场分布比普通介质波导Ex00模的场更集中在波导中部.同时,根据处理普通介质矩形波导的Marcatili方法.类比得到左手介质矩形波导表面模的色散方程,并数值模拟了低阶模的场分布,结果表明,能量主要集中在波导的四个角区以及波导的边缘.     

Analysis of non-linear multilayer waveguides with Kerr-like permittivities

This paper presents a semi-analytical method for calculating the dispersion relationships for stationary non-linear TE waves guided by general multilayer waveguides with Kerr-like permittivities. The non-linear wave equations are solved rigorously for each layer, and the mode index and field distribution are systematically determined so as to satisfy the boundary conditions at all interfaces. To verify the validity of the present method, a non-linear graded-index waveguide is approximated by a number of step layers and the resultant multilayer waveguide is analysed numerically. The convergence properties of mode index and total power flow are presented, and these are compared with direct solutions of the non-linear wave equation by the numerical integration method. The dispersion relationships for a non-linear multiple-quantum-well waveguide have also been investigated under two simple permittivity models. The present method is useful for the analysis of non-linear graded-index waveguides in addition to non-linear multilayer waveguides such as the multiple-quantum-well structure.     

两介质波导的最小中心间距

根据波导的耦合模理论,推导出两介质波导单位长度串扰的表达式,并在一定串扰的前提下,定义了两介质波导最小间距和最小中心间距,提出采用最小中心间距做为衡量波导集成度的参量.分析了波导尺寸及折射率差对最小间距、最小中心间距的影响.分析和模拟结果表明:折射率差越大,两波导最小间距、最小中心间距越小;在大折射率差的条件下,两波导最小间距可以降低到1 μm以下;在给定的工作波长、折射率分布的条件下,两介质波导的最小中心间距存在最小值.     

Study on guided-mode resonance characteristic of multilayer dielectric grating with broadband and wide using-angle

Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resonance is very important. In this paper the characteristics of guided-mode resonance in multilayer dielectric grating are studied with the aim of better understanding the physical process of guided-mode resonance and designing a broadband multilayer dielectric grating with no guided-mode resonance. By employing waveguide theory, all guided-wave modes appearing in multilayer dielectric grating are found, and the incident conditions, separately, corresponding to each guided-wave mode are also obtained. The electric field enhancement in multilayer dielectric grating is shown obviously. Furthermore, from the detailed analyses on the guided-mode resonance conditions, it is found that the reduction of grating period would effectively avoid the appearing of guided-mode resonance. And the expressions for calculating maximum periods, which ensure that no guided-mode resonance occurs in the requiring broad angle or wavelength range, are first reported. The above results calculated by waveguide theory and Fourier mode method are compared wit each other, and they are coincident completely. Moreover, the method that relies on waveguide theory is more helpful for understanding the guided-mode resonance excited process and analyzing how each parameter affects the characteristic of guided-mode resonance. Therefore, the effects of multilayer dielectric grating parameters, such as period, fill factor, thickness of grating layer, {\it et al.}, on the guided-mode resonance characteristic are discussed in detail based on waveguide theory, and some meaningful results are obtained.     

Light propagation in nonuniform plasmonic subwavelength waveguide arrays

We study light propagation in nanoscale periodic structures composed of dielectric and metal in the visible range. We demonstrate that diffraction curves of nonuniform waveguide arrays can be tailored by varying the geometric and dielectric features of the waveguides. The results obtained from a proper formulation of coupled mode theory for nonuniform arrays are validated through numerical solution of Maxwell equations in frequency domain.     

Enhancing Bremsstrahlung production from ultraintense laser-solid interactions with front surface structures

A new type of a coaxial multi-layer plasmonic waveguide is proposed. The mode propagation properties are analyzed at the communication working wavelength. Theoretical investigations reveal that the enhanced optical confinement can be achieved in the two low-index dielectric media layers. The mode size can be sub- or deep sub-wavelength scale. The mode propagation loss can be well compensated by replacing the high-index dielectric media with gain material to achieve longer propagation length with better mode confinement. The comparisons of the mode properties between the proposed waveguide and waveguides studied in the published literatures are also considered. These investigations potentially lay the groundwork for the further applications of nanowire type multilayer hybrid structures. This structure could also enable various applications such asnanophotonic waveguides, high-quality nanolasers, and optical trapping and biosensors.     

包含左手材料的四层平板波导中的光导模

研究一个芯子层是左手材料,其他三层由传统材料构成的四层平板光波导系统,利用图解法对各种TE偏振的导波模式的解进行详细分析.研究表明,四层左手材料光波导既能支持振荡导模,也能支持表面导模,与三层左手材料光波导相比较,此四层波导的导波模式呈现一些新的特性.对于中间传统材料层存在振荡场的情形:芯子层支持振荡导模的光波导中存在基模,并且高阶振荡导模出现模式缺失的性质;芯子层支持表面导模的光波导可以支持基模和多个高阶模式,并且存在模式兼并的性质.对于中间传统材料层存在衰减场的情形,此四层波导结构可等效为三层左手材料光波导.这些新的光波导传输性质对各种光波导器件的制作有潜在的应用价值.     

Analysis of rectangular-core waveguide structures and directional couplers by an iterated moment method

Using an iterated moment method (weighted index method), formulae are derived for the accurate calculation of the dispersion characteristics and field distributions of guided modes in strip dielectric waveguides and strip-loaded waveguides, and for the calculation of the coupling length of rectangular-core dual-channel directional couplers. The formulae are simple and the results obtained by the present analysis agree well with computer-aided exact numerical analysis. This method can be readily extended to the analysis of other dielectric waveguide structures.     

Analyzing the multilayer metamaterial waveguide structure with the Kerr-type nonlinear cladding

A general method for analyzing the multilayer metamaterial optical waveguides with the Kerr-type nonlinear cladding was proposed. To prove the accuracy of the proposed general method, a degenerated example was introduced. The analytical and numerical results show excellent agreement. The similar process can also be used to analyze TM waves propagating in the multilayer metamaterial waveguide structure with the Kerr-type nonlinear cladding.     

金属覆盖介质波导在截止点附近的光学特性

本文提出一种适合于截止点附近计算含金属覆盖层介质波层的近似解析方法，详细；地讨论在截止点附近的光波导的模式传播特性 和光电调制特性，并结合有效折射率方法讨论了止型脊形波导调制器的截止条件。     

Applications of the finite difference mode solution method to photonic crystal structures

The finite difference waveguide mode solution method, which has been popularly employed in the study of waveguide modes on various optical and dielectric waveguides, is utilized to calculate the modal characteristics of photonic crystal fibers (PCFs) and planar photonic crystal waveguides and the band diagrams of two-dimensional photonic crystals. Vector guided modes on both PCFs based on the total internal reflection guiding mechanism ('holey fibers') and those resulting from photonic band gap effect are accurately computed, with their effective indexes and field distributions compared with other methods. Calculated dispersion of a single-core holey fiber and coupled-power behavior of a two-core holey fiber are found to agree with measured results. For applications to band diagram calculation and planar photonic crystal waveguide analysis, the finite difference scheme is modified simply by imposing suitable periodic boundary condition. Numerical results for air-column crystals and dielectric-rod crystals are both found to agree well with calculations using other methods.     

All-dielectric bowtie waveguide with deep subwavelength mode confinement

Plasmonic waveguides and conventional dielectric waveguides have favorable characteristics in photonic integrated circuits. Typically, plasmonic waveguides can provide subwavelength mode confinement, as shown by their small mode area, whereas conventional dielectric waveguides guide light with low loss, as shown by their long propagation length. However, the simultaneous achievement of subwavelength mode confinement and low-loss propagation remains limited. In this paper, we propose a novel design of an alldielectric bowtie waveguide, which simultaneously exhibits both subwavelength mode confinement and theoretically lossless propagation. Contrary to traditional dielectric waveguides, where the guidance of light is based on total internal reflection, the principle of the all-dielectric bowtie waveguide is based on the combined use of the conservation of the normal component of the electric displacement and the tangential component of the electric field, such that it can achieve a mode area comparable to its plasmonic counterparts. The mode distribution in the all-dielectric bowtie waveguide can be precisely controlled by manipulating the geometric design. Our work shows that it is possible to achieve extreme light confinement by using dielectric instead of lossy metals.     

Optical field enhancement in nanoscale slot waveguides of hyperbolic metamaterials

Nanoscale slot waveguides of hyperbolic metamaterials are proposed and demonstrated for achieving large optical field enhancement. The dependence of the enhanced electric field within the air slot on waveguide mode coupling and permittivity tensors of hyperbolic metamaterials is analyzed both numerically and analytically. Optical intensity in the metamaterial slot waveguide can be more than 25 times stronger than that in a conventional silicon slot waveguide, due to tight optical mode confinement enabled by the ultrahigh refractive indices supported in hyperbolic metamaterials. The electric field enhancement effects are also verified with the realistic metal-dielectric multilayer waveguide structure.     

Mode order converter

We report experimental results with a simple mode order converter for dielectric slab waveguides. In particular we have shown conversion of higher order modes to the only mode of a monomode waveguide.     

High extinction ratio metal-insulator-semiconductor waveguide surface plasmon polariton polarizer

The attenuation characteristics of a multilayer metal clad GaAs-AlGaAs optical waveguide polarizer are theoretically investigated. The dispersion relations and field distribution of the multilayer structures are calculated for different geometrical parameters and material properties. The polarizer studied consists of a single mode finite/infinite metal clad GaAs-AlGaAs waveguide with a dielectric (SiO₂/Si₃N₄) buffer layer inserted between the metal and the waveguide.Conventionally, the TM polarized waves are found to exhibit an absorption peak at a particular buffer thickness (called critical buffer thickness).We shall show that the maximum TM absorption can be improved by a multiple factor up to 7 by choosing a buffer layer thicker than its critical value. This corresponds to an extinction ratio of 1470 dB for a polarizer length of 1 mm. Further, thicker buffers reduce the insertion losses and values as low as 0.1 dB can be obtained. The strong TM absorption in these structures is interpreted as resonant coupling of the guided mode to the lossy surface plasmon polariton supported by the thin metal film. Thicker buffer also reduces the TE losses (insertion losses) and hence increases the extinction ratio (ratio of TM to TE losses).This can be achieved by optimizing the buffer and the metal thicknesses. Another equally efficient polarizer can be designed by positioning a dielectric (same as buffer) layer (superstrate layer) above the metal film and then optimizing the buffer, metal and the superstrate thicknesses. We also show that the proposed polarizer with the superstrate layer is highly stable even when exposed to the extreme atmospheric changes.     

New method for calculating the spectra and radiation losses of leaky waves in multilayer optical waveguides

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties of which are determined by antiresonant reflection from the multilayer cladding (antiresonant reflecting optical waveguides) rather than by total internal reflection from the core-cladding interface as in standard optical waveguides. The new method applies to calculation of both electromagnetic modes in dielectric waveguides and electron quantum states in multibarrier semiconductor heterostructures. The characteristics of multilayer waveguides calculated by the new method are compared with published data obtained from a complex dispersion relation by the transfer matrix method. As an example, the wavelength dependence of the radiation losses for the first TE mode of a planar optical waveguide containing 52 pairs of layers is calculated.     

非线性平板光波导中TM波的网络分析

用横向等效网络方法分析了非线性平板波导中TM的色散关系和场分布.这种方法基于传输线理论,把非线性介质波导中复杂的电磁场问题等效于电路网络问题,用横向谐振技术得到色散方程.用数值方法计算了不同非线性机制下三层平板非线性波导中的TM波传输特性.     

Investigation of a UV-laser generated planar polymeric waveguide directly and after five years of preparation using an interferometric method

Polymeric integrated-optical waveguides were prepared in a planar chip using UV-laser lithographic method. Five waveguide samples were irradiated by an excimer laser of wavelength 248 nm with different irradiation parameters (fluence and irradiation doses). Using Mach–Zehnder interferometer, the refractive index depth profiles of these samples are determined in two cases, directly and five years later of preparation. A crucial change of refractive indices profiles has been recorded after five years of preparation. In the first case we got double region waveguides fitted a Gaussian shape, while in the second one we observe a single region waveguide which has exponential shape. The photochemical reactions responsible for these changes in the two cases are demonstrated. This is quite important when such waveguides are used in the applications. Also it was interesting to investigate the aging impact on mode field distributions and the effective mode indices. The mode parameters are determined based on a theoretical model and the experimentally obtained data. The results show a notable change in the mode field distributions and the propagation coefficients as influence of aging.     

The study of multilayer planar optical waveguide structure with nonlinear cladding

A novel method for analyzing the multilayer and multibranch optical waveguides with nonlinear cladding is presented. This method can also be used to analyze the multiple-quantum-well (MQW) waveguide structure. Numerical simulation results show that our analyses are reasonable.     

Measurements of refractive index profiles of proton－exchanged LiNbO_3 waveguidesusing TE－TM mode conversion

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