Polarization Beam Splitter Based on Self-Collimation Effect in Two-Dimensional Photonics Crystal

A photonic crystal polarization beam splitter based on the self-collimation effect is proposed. By means of the plane wave expansion method and the finite-difference time-domain method, we analyse the splitting mechanism in two alternative ways： performing a band gap structure analysis and simulating the field distribution. The results indicate that two beams of different polarizations can be split with an extinction ratio of nearly 20 dB in a wavelength range of POnm. The splitter may have practical applications in integrated photonic circuits.     

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.     

一种新型光子晶体波导定向耦合型超微偏振光分束器

将两个二维空气孔光子晶体波导平行放置,两波导之间由三排空气孔相隔,构成一个定向耦合器.数值分析了TE(磁场平行于空气孔)和TM(电场平行于空气孔)偏振态光波在该定向耦合器中的传播行为.结果表明,减小耦合区两波导间的一排介质柱的半径,TE模的耦合长度减小,而TM模的耦合长度不变.基于此结构,设计了超微偏振光分束器,整个器件的尺寸为10.1μm,与已报道的24.2μm的结果相比,该器件具有更小的器件尺寸和更高的输出效率.     

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric （TE） guided mode and transverse-magnetic （TM） guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguldes is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.Sttm. A finite-difference tlme-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.     

基于光子晶体自准直和带隙效应的马赫-曾德尔干涉仪设计

结合能带图和等频图分析,基于光子晶体自准直和光子带隙效应,设计了一种紧凑、高效的全光子晶体马赫-曾德尔(MZ)干涉仪.相应的光分束器和反射镜均由缺陷结构的光子晶体实现.讨论了干涉仪的输出机理,并与时域有限差分法(FDTD)模拟结果进行了比较.结果分析表明可以把MZ干涉仪作为一种气体、液体微型探测器.可在集成光学中起到重要的作用. 关键词： 光子晶体 自准直 MZ干涉仪     

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。     

Design of Ultra Compact Polarization Splitter Based on the Complete Photonic Band Gap

A novel design of polarization splitter based on the complete photonic band gap has been proposed in this paper. The proposed Photonic Band Gap (PBG) polarization splitter is formed by two photonic crystal waveguides composed of dielectric rods in air in honeycomb structure for which complete photonic band gap is obtained using the plane wave expansion (PWE) method. The splitting properties (i.e. coupling length, extinction ratio and insertion loss) of PBG polarization splitter have numerically been investigated using the finite difference time domain (FDTD) method. It has been shown that polarization splitter of length as small as 32 μm can be designed at λ=1.55 μm. The proposed polarization splitter offers a large bandwidth of 120 nm.     

Emissions of Photonic Crystal Waveguides with Discretely Modulated Surfaces

Transmission properties of photonic crystal （PC） waveguides with discretely modulated exit surfaces are investigated numerically using the finite-difference time-domain （FDTD） method. Unlike the case of periodically modulated surfaces, where the transmission beam tends to be a single and directional beam, when the exit surfaces are modulated only at several discrete points, the emission power tends to split into multiple and directional beams. We explain this phenomenon using a multiple point source interference model. Based on these results, we propose a 1-to-N beam splitter, and numerically realized high efficiency coupling between a PC sub-wavelength waveguide and three traditional dielectric waveguides with a total efficiency larger than 92%. This simple, easy fabrication, and controllable mechanism may find more potential applications in integrated optical circuits.     

多功能磁光子晶体太赫兹可调偏振控制器件

通过对磁场控制下的二维磁光子晶体太赫兹波偏振传输特性的研究,利用铁氧体磁光材料的磁导率随外磁场改变而变化的特点,设计了具有可控起偏、偏振分束和可调谐波片功能的光子晶体太赫兹偏振控制器件.利用平面波展开法和严格耦合波分析分别计算了光子晶体带隙位置和透过率随外磁场强度变化的关系,用时域有限差分法计算了场分布和相位.结果表明,该结构可以实现高偏振消光比的偏振起偏器和分束器,以及在1 THz附近-π-π相位范围的连续可调谐波片. 关键词： 太赫兹 光子晶体 铁氧体 偏振控制     

Optical Coherence Tomography Implemented by Photonic Crystal Fiber

We report a photonic crystal fiber (PCF)-based optical coherence tomography (OCT) system, in which conventional single-mode fiber for the transmission line and the fiber coupler for the beam splitter/combiner are replaced with PCF and PCF coupler. The PCF coupler fabricated using the fused biconical tapered (FBT) method showed a nearly flat coupling ratio over a broad spectral bandwidth of 400 nm, which provided an axial resolution of 3-μm for OCT imaging. With a white-light source, the 8-μm thick air gap between two stacked cover glasses was measured, and with a conventional superluminecent diode (SLD) source, the in vitro images of rat eye and Misgurnus mizolepis skin were successfully obtained. The PCF and PCF coupler might enable a white-light as the source for the cost effective and high-resolution OCT system.     

基于各向异性介质的偏振分束器

利用各向异性介质与各向同性介质构造了一维光子晶体,利用传输矩阵方法分析了它的能带结构,指出利用各向异性介质可以构造高消光比,全角度的偏振分束器件,并分析了它的理论基础.对影响偏振分束带宽的因素进行了分析.为进一步改进设计提出了方向.     

双光子吸收对光子晶体定向耦合全光开关的影响

 利用时域有限差分方法,在非线性条件下,考虑双光子吸收效应的同时,建立了分析2维光子晶体定向耦合波导光开关的模型。数值计算结果表明,对于长度较短的波导耦合器件,在强控制光和非线性条件下,双光子吸收效应会对波导的耦合作用产生一定的影响,从而改变入射光的透射特性,使光开关控制的动态过程发生变化。故而在设计全光开关器件时,对强控制光条件下的非线性双光子吸收效应有必要作为影响因素考虑进去。     

Polarization beam splitter based on a photonic crystal heterostructure

The design and characterization of a photonic crystal (PC) polarization beam splitter (PBS) that operates with an extinction ratio of greater than 15 dB for both polarizations are presented. The PBS is fabricated on a silicon-on-insulator (SOI) wafer where the input and output ports consist of 5 mum wide ridge waveguides. A large spectral shift is observed in the dispersion plots of the lowest-order even (TE-like) and odd (TM-like) modes due to the SOI confinement. Because of this shift, the TE-like mode is close to a directional gap at the top of the band, and the TM-like mode is in a low-frequency regime where the dispersion surface is almost isotropic. We show that the TE-like mode has very high reflection at the interface between the two PCs, whereas the TM-like mode exhibits a very high transmission.     

Performance Investigation of Photonic Crystal-Based Microring Resonator for Optical Signal Processing

Abstract

A detailed theoretical analysis is presented to characterize wave propagation at 1,550 nm inside a glass (SiO₂) microring resonator implemented using photonic crystal technology. A photonic crystal reflection is used at each microring resonator corner to enhance the bending efficiency. The characteristics of both photonic crystal beam splitter and microring resonator bending losses are analyzed and investigated using both effective refractive index and finite difference time domain methods. Analytical expressions are also derived to describe the field enhancement inside the microring resonator, the transfer function of the microring resonator, and the main parameters characterizing the resonator such as resonator band width and quality factor. The analysis is also extended to characterize a drop filter implemented using photonic crystal-based microring resonator. The results indicate clearly that the effective refractive index method can give accurate results if one starts the calculations with finite difference time domain-estimated beam splitter parameters. Further, bending efficiency as high as 99% can be obtained using a ten-post layer photonic crystal mirror at each microring resonator corner.     

光子晶体中基于有效折射率接近零的光束准直出射

利用平面波展开法(PWM)和时域有限差分法(FDTD)研究了二维正方格子光子晶体靠近禁带边沿附近频率光波的传输特性.研究发现,若有效折射率接近于零,可出现光束从晶体表面准直出射的现象,且光束的出射方向只与晶体表面的取向有关,而与晶格取向无关.这种现象与自准直现象有很大不同.     

Enlargement of complete two-dimensional band gap by using photonic crystal heterostructure

A two-dimensional photonic crystal heterostructure, which consists of two photonic crystals of a square lattice of circular columns with reverse dielectric configurations, is proposed. Photonic band gap properties are calculated using a plane-wave method and the transmission spectra are obtained. After optimization, the relative width of the complete band gap reached 13.8% based on the simple unit-cell shape and crystal lattice. The photonic crystal heterostructure opens up new ways of engineering photonic band gap materials and designing photonic crystal devices.     

A novel optical beam splitter based on photonic crystal with hybrid lattices

A novel optical beam splitter constructed on the basis of photonic crystal(PC) with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process.     

液晶调制的光子晶体可控偏光片和光开关

与介质柱型光子晶体相比，空气孔光子晶体更易于制作和集成而更有应用价值.采用平面波展开法证实了填充液晶的二维三角形分布的空气孔光子晶体方向能隙的可调节性.数值模拟结果表明：1)通过外界电场控制空气孔中所填充的相列液晶的方向可以对光子晶体的方向能隙进行调节，这种可调节性可用于制作场敏偏光片.这与Liu等人研究介质柱型光子晶体的结论相类似；2)用phenylacetylene型液晶替代5CB液晶作为填充物质所得到的空气孔光子晶体偏光片可使用的频率范围显著增大.在此基础上，还研究了填充液晶的光子晶体波导传输谱线的可调节性对特定波长的光切断和开通控制的原理，实现了与以往光开关原理不同的光子晶体光开关. 关键词： 光子晶体 液晶 可调节性 平面波展开法 场敏偏光片     

红外区二维光子晶体偏振分光镜透射谱分析

采用时域有限差分（Finite-Difference Time-Domain,FDTD）法模拟了垂直入射红外波段二维光子晶体偏振分光镜的透射谱,从而验证了用平面波展开方法计算的二维光子晶体能带结构.用电子束蒸发方法在光栅基板上制备了Ge/BaF2多层膜,实现了二维光子晶体偏振分光镜.实验初步证明了这种光子晶体在垂直入射时具有偏振特性,分析了实验结果与理论计算之间偏差的产生原因.     

Experimental demonstration of self-collimation beaming and splitting in photonic crystals at microwave frequencies

I studied experimentally beam self-collimation and splitting in two-dimensional microwave photonic crystals. Using a microwave photonic crystal fabricated from alumina rods, I present an experimental proof of principle for an earlier theoretical proposal [A.F. Matthews, S.K. Morrison, Yu.S. Kivshar, Opt. Commun. 279 (2007) 313] of a photonic crystal beam splitter based on the self-collimation effect.