三平行光子晶体单模波导的耦合特性及其应用

将三光子晶体单模波导的相互耦合看成一个多模干涉系统.本征模的色散曲线相交或近于相交并出现简并模，简并模之间存在强烈耦合并导致模式的分布方式发生转变.多模干涉系统中，不同波长的光波能量在传输过程中由于相干而具有不同的空间输出行为，在近简并点处多模之间的相干解除，能流限制在原输入方向，不发生转移.三光子晶体单模光波导的这种特性可用来制作波分复用或解复用器件. 关键词： 光子晶体波导 简并模 多模干涉 波分复用或解复用     

平行光子晶体波导的传输特性及应用

采用时域有限差分法研究两平行光子晶体波导的传输特性及模场分布,利用耦合模理论计算光子晶体波导的耦合系数。计算结果表明,在不同的频率范围内两平行光子晶体波导之间表现出不同的耦合特性:在高频段(0.32~0.44)(ωa/2πc)的范围内两直波导表现出相互的能量交换,实现光耦合,耦合系数随入射波 频率增加而减小;而在低频段(0.29~0.32)(ωa/2πc)的范围内,两波导的传输谱图几乎重合。最后,提出一种采用固定波导耦合长度同时实现光分束及光均分器的方案,当耦合长度取34a时,可将频率为0.333 (ωa/2πc)和 0.357(ωa/2πc)的两入射波分束传播,同时将低频段中的任意频率波进行能量均分。     

基于波导间能量耦合效应的光子晶体频段选择与能量分束器

基于波导间能量耦合效应的光子晶体功率分束器具有结构紧凑、带宽较宽、弯曲损耗低、分光角度大和不受外界电磁场干扰等优点.本文利用时域有限差分方法,理论研究了二维三角晶格光子晶体耦合波导的功率分束特性,设计得出了一种能够在宽频谱范围内针对不同频率区间实现不同分光比的功能器件.在此基础上通过改变耦合区介质柱形状以及输出分支波导与能量耦合波导的连接位置,最终针对三个相邻频率范围内的入射光信号,较好地实现了三均分、二均分、单一输出通道这3种能量分配输出模式.该功能器件具有透过率对比度高、结构紧凑等特性,对于发展全光功能器件在大规模全光复杂集成领域内的实际应用具有一定的促进作用.     

光子晶体耦合波导实现光开关效应的研究

提出了一种基于光子晶体耦合波导实现光开关效应的方法:将线缺陷引入二维光子晶体以形成两平行的邻近波导,两邻近波导及其中间的两排介质柱构成了光开关模型耦合区;利用平面波展开法计算了不同介质填充率情况下的色散特性.结果发现:减小介质填充率可以实现波导耦合长度的减小;分段调整中间介质柱的填充率和选择不同的耦合搭配长度,定向耦合...     

Design of photonic crystal power couplers via gratinglike surfaces

This work deals with the inverse design in the field of photonic crystal based devices. We use the finite-difference time-domain method in conjunction with a genetic algorithm to design a power coupler between two photonic crystal waveguides. By optimizing the structure of gratinglike surfaces added near the photonic crystal waveguides, we have obtained several simple power couplers considering different coupling lengths. These couplers have high coupling efficiency as well as high power intensity in the propagation direction.     

Coupling into slow-mode photonic crystal waveguides

We study efficient injectors for coupling light from z-invariant ridge waveguides into slow Bloch modes of single-row defect photonic crystal waveguides. Two-dimensional vectorial computations performed with a Bloch mode theory approach predict that very high efficiencies (>90%) can be achieved for injector lengths of only a few wavelengths in length, even for small group velocities in the range of c/100-c/400. This result suggests that photonic crystal devices operating with slow waves can be interfaced with classical waveguides without sacrificing compactness.     

Contra-directional coupling between two-dimensional photonic crystal waveguides

The contra-directional coupling between two photonic crystal (PC) waveguides is studied, using the finite-difference time-domain (FDTD) method. A design of contra-directional coupler is presented and its transmission properties are investigated. The device can be used as an add/drop filter. It is also shown that the coupled mode theory is suitable to study the photonic crystal waveguide coupler.     

基于自映像的光子晶体波导分束器的设计

通过研究2维正方晶格光子晶体波导多模干涉的自映像效应,优化设计了一种新型1×2光子晶体波导分束器,采用时域有限差分法对其传输特性进行模拟分析。设计过程中,根据多模干涉耦合区中周期出现的双重像的位置确定两个单模输出波导的位置,通过在分束器输入和输出耦合区的连结处设置介质柱,改变输入和输出耦合区中的模场分布,实现模式匹配,从而明显减小分束器的反射损耗。计算结果表明:设置的介质柱归一化半径分别为0.08和0.177时,对于波长为1.55μm的入射光,该分束器的透射率可高达93%。     

Adiabatic coupling between conventional dielectric waveguides and waveguides with discrete translational symmetry

We study adiabatic transformation in optical waveguides with discrete translational symmetry. We calculate the reflection and transmission coefficient for a structure consisting of a slab waveguide that is adiabatically transformed into a photonic crystal waveguide and then back into a slab waveguide. The calculation yields high transmission over a wide frequency range of the photonic crystal waveguide band and indicates efficient coupling between the slab waveguide and the photonic crystal waveguide. Other applications of adiabatic mode transformation in photonic crystal waveguides and the coupled-resonator optical waveguides are also discussed.     

光子晶体定向耦合三波长功分器

以二维三角晶格光子晶体为研究对象,在该光子晶体中引入两行以一行耦合介质柱为间距的平行单模线缺陷波导.通过分析和研究光子晶体波导耦合结构的耦合和解耦合特性,发现在不同频率下耦合波导的耦合长度不同.利用平面波展开法和定向耦合原理计算了在不同入射光频率下,缺陷波导间耦合波导的耦合长度,设计了一种新型超微光子晶体波导耦合型三波长功分器,实现了归一化频率分别为0.369、0.394、0.435的光波的分束效果.采用时域有限差分法验证了该功分器具有很好的功率分配效果.本文结果有助于光子晶体新型滤波器、定向耦合器、波分复用器、偏振光分束器以及光开关等光子器件的研究.     

Numerical characterization of nanopillar photonic crystal waveguides and directional couplers

We numerically characterize a novel type of a photonic crystal waveguide, which consists of several rows of periodically arranged dielectric cylinders. In such a nanopillar photonic crystal waveguide, light confinement is due to the total internal reflection. A nanopillar waveguide is a multimode waveguide, where the number of modes is equal to the number of rows building the waveguide. The strong coupling between individual waveguides leads to the proposal of an ultrashort directional coupler based on nanopillar waveguides. We present a systematic analysis of the dispersion and transmission efficiency of nanopillar photonic crystal waveguides and directional couplers. Plane wave expansion and finite difference time domain methods were used to characterize numerically nanopillar photonic crystal structures both in two- and three-dimensional spaces.     

Grating-assisted coupling of optical fibers and photonic crystal waveguides

We propose and analyze a highly efficient method of coupling light from optical fibers to two-dimensional photonic crystal waveguides. Efficient coupling is achieved by positioning of a tapered fiber parallel to the linear defect, where the photonic crystal's cladding functions as a grating coupler and provides field confinement as well. Numerical simulations indicate that better than 90% transmission is possible with a full width at half-magnitude bandwidth of 12nm. It is shown that one can increase the bandwidth by increasing the field overlap between the two waveguides.     

二维光子晶体平行多波导的传输光谱研究

采用时域有限差分法研究二维光子晶体两平行直波导以及三平行直波导的传输特性。计算结果表明,两平行波导在不同的频率范围内表现出不同的耦合特性：在高频段两波导表现出相互的能量交换,实现光耦合,而在低频段传输谱图重合,各波导传输光强均为入射光强的二分之一;对于三波导系统,发现在不同的频率范围内主波导与两耦合波导之间也表现出不同的耦合特性：在高频段两耦合波导与主波导实现光耦合,而在低频段两耦合波导与主波导的传输谱图同步变化,耦合波导的传输光强均约为入射光强的四分之一。     

Efficient transmission in cascaded photonic crystal waveguides via a strong coupling effect

A design of cascaded photonic crystal waveguide is proposed in this paper inspired by the work of Tang et al. [D. Tang, L. Chen, W. Ding, Appl. Phys. Lett. 89 (2006) 131120]. In contrast to a conventional waveguide source, a plane wave source is applied in the current design. We show that an efficient guide mode in the photonic band gap can be achieved. The same idea also works for a slight variation by defects introduction in the photonic crystal. Finally, the strong coupling effect present in the cascaded waveguides is demonstrated by an analogy with photonic quantum wells.     

基于硅纳米线波导的两级光子晶体缩束器

鉴于在微观领域光波的缩束对实现光电集成的重要意义,提出了基于硅纳米线波导的两级光子晶体缩束器。其中一级压缩基于W5型和W1型光子晶体波导间的高效耦合。二级压缩则由宽为0.1μm,长为3.06μm的纳米线波导和W1型光子晶体波导构成,通过二者的高效耦合实现光束压缩。当W1型光子晶体波导和纳米线波导间介质柱的半径为0.04μm时,对于1550nm波长的电磁波,缩束器的通光效率可达93.4%,压缩比为16.08,出射光束半峰全宽仅为0.148μm。     

Beaming effect in multimode photonic crystal by using coupled waveguides

Beaming effect of a multimode photonic crystal (PC) covered by a waveguide array on the exit plane is investigated theoretically. The simulation results show that the multimode PC can make the incident light split into two beams, which can be regarded as secondary sources radiating light into the waveguide array. As a result, many light beams can be generated in the array by the coupling among the waveguides, and the interference of these light beams after passing the system leads to directional emission. Additionally, the directional emission is greatly affected by the beam distribution on the exit plane of the system. Once the main light beams are formed on the exit plane of the system by modulating the system size, steady beaming effect can be obtained in the horizontal direction.     

基于全内反射光子晶体多模波导偏振无关型光分束器

研究了全内反射在光子晶体多模波导中的作用,利用常规的耦合模理论对对称入射时的多模干涉行为和自映射现象进行了讨论和分析.研究表明,输入光场依然能沿着多模导光区高效的传输,这种结构中的光场传输是由全内反射和布喇格反射的联合作用而决定的.设计了一种全内反射偏振无关型光分束器,这种分束器在集成光学中具有重大的潜在应用价值.     

Experimental realization of highly efficient broadband coupling of single quantum dots to a photonic crystal waveguide

We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to a photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements beta-factors of up to 0.89 are derived, and an unprecedented large bandwidth of 20 nm is demonstrated. This shows the promising potential of photonic crystal waveguides for efficient single-photon sources. The scaled frequency range over which the enhancement is observed is in excellent agreement with recent theoretical proposals taking into account that the light-matter coupling is strongly enhanced due to the significant slow-down of light in the photonic crystal waveguides.     

光子晶体波导耦合的波分复用研究

两平行光子晶体单模波导的相互耦合组成一个耦合结构。两本征模的色散曲线相交并出现简并,简并模之间的耦合作用使模式的分布发生了改变。由于耦合的作用,各个波长的光波会在不同的波导中传输。在简并点处两本征模发生解耦合,光波会沿着原来的方向传输。将两个不同耦合长度的光子晶体波导耦合结构集成在一起,就可以组成一个三波长的光子晶体波分复用器。     

A compact wavelength division de-multiplexer based on directional coupling of one-dimensional photonic crystal waveguides

A fundamental dual-channel wavelength division de-multiplexer (WDDM) based on directional coupling of one-dimensional photonic crystal waveguides is presented, and its transmission characteristics of the WDDM are investigated by using finite-difference time-domain method. Calculated results indicate that for this WDDM, without any structural optimization, a high transmittance of more than 95% is observed at output ports. Combining the fundamental dual-channel WDDM with flexible bends of one-dimensional photonic crystal waveguides, we construct a simple and compact four-channel WDDM. Those WDDMs are expected to be applied to highly dense photonic integrated circuits.