跑道型结构光子晶体波导定向耦合器

鉴于波导定向耦合器在集成光路以及光电集成方面的广泛应用,提出了一种基于光子晶体波导间高效耦合的光子晶体定向耦合器。通过主波导和耦合波导间的耦合,可以实现对波长为1 490 nm和1 550 nm电磁波的高效分光。在将器件长度控制在30 μm左右的同时,其总效率高达93.05%。另外,发现主波导和耦合波导间介质柱结构参数对电磁波的耦合周期有着极大的影响。并通过将介质柱沿z方向拉伸0.1a(a为晶格周期),设计了工作波长为1 530 nm和1 540 nm的光子晶体定向耦合器,器件长度仅为60 μm。通过拉伸介质柱的纵向长度,可以大幅减小耦合周期,这对缩小器件体积以及实现更为密集的波分复用有着重要的意义。     

并联谐振腔光子晶体单通道侧面耦合波导

分析了多光子晶体谐振腔的并联耦合模理论,并根据该理论设计了单通道光子晶体侧面耦合波导以实现光子晶体器件与光源间的高效耦合。理论研究表明并联谐振腔的耦合效率与谐振腔数量、间距以及品质因子相关。经优化耦合面积和耦合效率,最终选择了5个谐振腔并联作为单通道侧面耦合波导的耦合部分。通过设置谐振腔间距改变其对称性,从而实现侧面耦合波导的单通道传播。在1.55μm工作波长下,单通道侧面耦合波导的耦合效率可达94.49%。     

基于混合导光型光子晶体光纤的波分解复用器研究

设计了一种基于混合导光型光子晶体光纤的波分解复用器,该波分解复用器同时具有折射率导光型光子晶体光纤和带隙导光型光子晶体光纤的特点,可用于稀疏型波分复用系统中.设计的稀疏型波分解复用器由一段三芯光子晶体光纤组成,通过填充不同折射率的材料.形成了混合导光型光子晶体光纤.根据耦合模原理,在临近的波导中,当传播常数相等时,模式之间发生强烈耦合.能量在波导之间交替.由于填充的材料折射率不同,使得光功率在两个小同的波长上发生耦合,构成了两个不同响应波长的光滤波器.通过选择合适的光纤长度,使得在光纤的输出端,不同波长的光从不同的波导输出,实现波分解复用的功能.采用全矢量有限元法分析了光纤传输特性,计算了不同波长光的耦合长度.采用光束传播法仿真发现,长度为4.3 mm的光纤能实现波长为1.31μm和1.55μm光的解复用.     

二维正方晶格光子晶体三光波导方向耦合器

光子晶体是以介电常数呈周期性排布且在光波长量级构建的人工微结构,利用其具有光子禁带这一特性可实现对光子的控制。引入线缺陷可形成光子晶体波导。以1.55μm的TE偏振光作为光源,用时域有限差分法计算并分析了二维正方晶格光子晶体三光波导方向耦合器在不同波导间距下的耦合长度及耦合效率分别与介质柱折射率和介质柱半径的变化关系。研究结果为1.55μm耦合器的结构设计及制备提供一定的理论指导。     

利用耦合波导列提高光子晶体波导辐射

将耦合波导列应用于光子晶体单模波导,提出一种提高光辐射的光子晶体结构. 基于时域有限差分方法的理论研究表明,当将耦合波导列附加到单模光子晶体波导出口端的适当位置,使出射光分成若干强弱不一的光束,这些光束在传播空间通过干涉形成一定程度的汇聚,大大提高了光子晶体波导在水平方向的光辐射效率. 另外,当耦合波导列的行数大于某固定值(2N=8)时,辐射质量基本保持不变,由此可获得最紧凑的器件结构. 这种类型光子晶体在近场光学和集成光学等诸多方面有潜在的应用价值. 关键词： 光子晶体波导 光辐射 波导列 耦合波导     

大模面积掺Yb~(3+)七芯光子晶体光纤的设计

要提高七芯光子晶体光纤激光器的输出功率,必须要增大七芯光子晶体光纤的有效模面积,并且需要纤芯间具有较强的耦合作用,以保证各纤芯输出的光束保持同相位。为了更直观的分析七芯光子晶体光纤的有效模场面积和纤芯间耦合强度的关系,根据七芯光子晶体光纤7个超模的特征,给出了七芯光子晶体光纤耦合长度的一种计算方法。利用多极法和有限差分光束传播法分析了七芯光子晶体光纤的结构对有效模场面积和耦合长度的影响。通过优化七芯光子晶体光纤的结构,设计了一种外层空气孔较大,内层空气孔较小的七芯光子晶体光纤,其有效模场面积高达3703μm2,耦合长度仅为13310μm。     

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.     

高透射率慢光速的光子晶体耦合腔波导的研究

将二维三角晶格光子晶体波导和微腔结构结合,优化设计了一种二维三角晶格光子晶体共振耦合腔波导,运用时域有限差分法(FDTD)模拟共振耦合腔波导TE偏振光的透射谱,通过透射谱得到传输光的透射率和群速度。结果表明,合适参数的二维三角晶格共振耦合腔波导在波长1.551μm处的群速度为c/130、透射率为20.1%,在波长1.502μm处的群速度为c/50、透射率为29.2%。运用平面波展开法(PWE)计算的该波导的能带结构对慢光特性进行了分析。这种慢光特性的光子晶体波导将在光存储、光延迟及光子集成等方面有潜在的应用价值。     

高效异质结构四波长波分复用器的设计与优化

将两光子晶体单模波导平行、邻近放置构成一个光子晶体波导耦合结构.根据耦合和解耦合理论,设计了一种新型的高效异质结构四波长波分复用器.应用时域有限差分法模拟了该器件的效率,并通过改变一排介质柱的折射率,实现了较高的透射率.进一步发现在入射口处添加三对介质柱,可以有效地降低系统的反射,实现了四个波长的高效传输,四个波长的透射率均超过了90%.该器件不仅具有较高的透射率,而且其尺寸仅为36 μm×17 μm,在未来的光子集成回路中具有潜在的应用价值. 关键词： 光子晶体波导 耦合 异质结构 波分复用     

基于二维非线性光子晶体的全光开关特性

为获得一个优化的全光开关结构,在光子晶体90°弯曲波导的基础上,进一步改进光子晶体结构,并在其中加入克尔型非线性介质柱,得到了非线性光子晶体全光开关结构。通过时域有限差分(FDTD)法数值分析表明,该开关结构能够实现的带宽大约为50nm,消光比大于40dB,阈值功率密度约为5.2W/μm。同时,该结构还可以实现基本的逻辑功能。     

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.     

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.     

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.     

Gap maps, diffraction losses, and exciton–polaritons in photonic crystal slabs

A theory of photonic crystal (PhC) slabs is described, which relies on an expansion in the basis of guided modes of an effective homogeneous waveguide and on treating the coupling to radiative modes and the resulting losses by perturbation theory. The following applications are discussed for the case of a high-index membrane: gap maps for photonic lattices in a waveguide; exciton–polariton states, when the PhC slab contains a quantum well with an excitonic resonance; propagation losses of line-defect modes in W1 waveguides, also in the presence of disorder; the quality factors of photonic nanocavities. In particular, we predict that disorder-induced losses below 0.2 dB/mm can be achieved in state-of-the-art samples by increasing the channel width of W1 waveguides.     

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%。     

Subpicosecond pulse compression in nonlinear photonic crystal waveguides based on the formation of high-order optical solitons

We investigate by numerical simulation the compression of subpicosecond pulses in two-dimensional nonlinear photonic crystal (PC) waveguides. The compression originates from the generation of high-order optical solitons through the interplay of the huge group-velocity dispersion and the enhanced self-phase modulation in nonlinear PC waveguides.Both the formation of Bragg grating solitons and gap solitons can lead to efficient pulse compression. The compression factors under different excitation power densities and the optimum length for subpicosecond pulse compression have been determined. As a compressor, the total length of the nonlinear PC waveguide is only ten micrometres and therefore can be easily incorporated into PC integrated circuits.     

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.     

Four-port coupled channel-guide device based on 2D photonic crystal structure

We have fabricated and measured a four-port coupled channel-waveguide device using W1 channel waveguides oriented along ΓK directions in a two-dimensional (2D) hole-based planar photonic crystal (PhC) based on silicon-on-insulator (SOI) waveguide material, at operation wavelengths around 1550 nm. 2D FDTD simulations and experimental results are shown and compared. The structure has been designed using a mode conversion approach, combined with coupled-mode concepts. The overall length of the photonic crystal structure is typically about 39 μm and the structure has been fabricated using a combination of direct-write electron-beam lithography (EBL) and dry-etch processing. Devices were measured using a tunable laser with end-fire coupling into the planar structure.