Extreme narrow photonic passbands generated from defective two-segment-connected triangular waveguide networks

In this paper, we investigate the optical transmission properties of perfect and defective two-segment-connected tri- angular waveguide networks （2SCTWNs） and find that after introducing defects in networks, many groups of transparent extreme narrow photonic passbands （ENPPs） will be created in the middle of the transmission spectra, the number for each group and the group number of ENPPs can he adjusted by the matching ratios of waveguide length （MRWLs）, the number of defects, and the number of unit cells of 2SCTWNs. The influences of MRWL, number of defects, and number of unit cells on the number, width, and position of these ENPPs are researched and a series of quantitative rules and prop- erties are obtained. It may be useful for the designing of high-sensitive optical switches, wavelength division multiplexers, extreme-narrowband filters, and other correlative waveguide network devices.     

Large photonic band gaps and strong attenuations of two-segment-connected Peano derivative networks

In this Letter, based on ancient Peano curves we construct four kinds of interesting Peano derivative networks composed of one-dimensional (1D) waveguides and investigate the optical transmission spectra and photonic attenuation behavior of electromagnetic (EM) waves in one- and two-segment-connected networks. It is found that for some two-segment-connected networks large photonic band gaps (PBGs) can be created and the widths of large PBGs can be controlled by adjusting the matching ratio of waveguide length and are insensitive to generation number. Diamond- and hexagon-Peano networks are good selectable structures for the designing of optical devices with large PBG(s) and strong attenuation(s).     

Huge photonic band gaps with strong attenuations resulted from quasi-one-dimensional waveguide networks composed of triangular fundamental loops

In order to design systems generating large photonic band gaps (PBGs), in this paper we construct interesting quasi-one-dimensional (quasi-1D) periodic triangular, diamond, and tetrahedral networks composed of 1D waveguides and triangular fundamental loops. The optical frequency band structures and photonic attenuation behaviors of electromagnetic (EM) waves propagating in the three kinds of one- and two-segment-connected (1SC and 2SC) networks without dissipation are, respectively, investigated and we find that huge PBGs can be produced in the middle of a frequency period and the widths of the largest PBGs can be controlled by adjusting the matching ratio of waveguide length. When the ratio equals 2:1, the width of the hugest PBG resulted in tetrahedral network reaches 0.73 times of a frequency period and is about 1.16 times of the best result reported previously. The average attenuations of the largest PBGs are very strong and increase rapidly with the increment of the number of unit cell. This makes our designed networks with very few unit cells exhibit wonderful PBG features and they can be realized in experiments easily. It may be useful for the designing of optical devices with large PBG and strong attenuation.     

二维光子晶体线缺陷结构的光谱辐射特性

光子晶体的禁带特性是该新兴材料的最根本特征。本文运用平面波展开法(PWE)计算了一种正方晶格Si光子晶体材料的禁带特性,并基于该材料设计出一种红外波段的线缺陷光子晶体波导结构。运用时域有限差分法(FDTD)研究了线缺陷二维光子晶体波导宽度对通频带、电场强度及透射能量的影响,研究结果为二维光子晶体波导器件的开发和利用提供了理论支撑。     

Large photonic band gap and strong attenuation of multiconnected Peano network

In this paper, by means of the network equation and generalized eigenfunction method we investigate the optical transmission spectra and attenuation behavior of electromagnetic (EM) waves in multiconnected Peano networks composed of one-dimensional (1D) waveguides. It is found that for some two-segment-connected networks a very large photonic band gap (PBG) can be created in the middle of a frequency period and the width of the large PBG can be controlled by adjusting the matching ratio of waveguide length, d₂ : d₁. When d₂ : d₁ = 2 : 1, the width of the large PBG is bigger than half of frequency period. The influence of generation on the width and attenuation of the large PBG are also studied and the numerical results demonstrate that the first-generation Peano network with d₂ : d₁ = 2 : 1 is a good selectable structure for the designing of optical devices with large PBG and strong attenuation.     

Numerical study on characteristic of two-dimensional metal/dielectric photonic crystals

An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of twodimensional(2D) metal/dielectric photonic crystals.Based on the photonic band structures,the dependence of flat bands and photonic bandgaps on two parameters(dielectric constant and filling factor) are investigated for two types of 2D metal/dielectric(M/D) photonic crystals,hole and cylinder photonic crystals.The simulation results show that band structures are affected greatly by these two parameters.Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters.It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones,and the frequency ranges of bandgaps also depend strongly on these parameters.Besides,the photonic crystals containing metallic medium can obtain more modulation of photonic bands,band gaps,and large effective refractive index,etc.than the dielectric/dielectric ones.According to the numerical results,the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.     

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.     

Pressure, temperature and plasma frequency effects on the band structure of a 1D semiconductor photonic crystal

In this work using the transfer-matrix formalism we study pressure, temperature and plasma frequency effects on the band structure of a 1D semiconductor photonic crystal made of alternating layers of air and GaAs. We have found that the temperature dependence of the photonic band structure is negligible, however, its noticeable changes are due mainly to the variations of the width and the dielectric constant of the layers of GaAs, caused by the applied hydrostatic pressure. On the other hand, by using the Drude's model, we have studied the effects of the hydrostatic pressure by means of the variation of the effective mass and density of the carriers in n-doped GaAs, finding firstly that increasing the amount of n-dopants in GaAs, namely, increasing the plasma frequency, the photonic band structure is shifted to regions of higher frequencies, and secondly the appearance of two regimes of the photonic band structure: one above the plasma frequency with the presence of usual Bragg gaps, and the other, below this frequency, where there are no gaps regularly distributed, with their width diminishing with the increasing of the plasma frequency as well as with the appearance of more bands, but leaving a wide frequency range in the lowest part of the spectrum without accessible photon states. Also, we have found characteristic frequencies in which the dielectric constant equals for different applied pressures, and from which to higher or lower values the photonic band structure inverts its behavior, depending on the value of the applied hydrostatic pressure. We hope this work may be taken into account for the development of new perspectives in the design of new optical devices.     

Photonic bands, gap maps, and intrinsic losses in three-component 2D photonic crystal slabs

We obtain the photonic bands and intrinsic losses for the triangular lattice three-component two- dimensional （2D） photonic crystal （PhC） slabs by expanding the electromagnetic field on the basis of waveguide modes of an effective homogeneous waveguide. The introduction of the third component into the 2D PhC slabs influences the photonic band structure and the intrinsic losses of the system. We examine the dependences of the band gap width and gap edge position on the interlayer dielectric constant and interlayer thickness. It is found that the gap edges shift to lower frequencies and the intrinsic losses of each band decrease with the increasing interlayer thickness or dielectric constant. During the design of the real PhC system, the effect of unintentional native oxide surface layer on the optical properties of 2D PhC slabs has to be taken into consideration. At the same time, intentional oxidization of macroporous PhC structure can be utilized to optimize the design.     

Group index and dispersion properties of photonic crystal waveguides with circular and square air-holes

The slow light and group velocity dispersion properties of 2D triangular lattice photonic crystal line defect waveguide (PCW) with square and circular air-holes are numerically investigated with the plane-wave expansion method. The simulation results show that the guided mode is impacted slightly by the cross section’s shape of the air-holes of the same filling ratio. Adjusting two rows of the inner-hole adjacent to the waveguide and modifying the waveguide width can bring in low-group velocity and low-dispersion (LVLD) region, in which the group index of the square holes can reach 210 which is far better than the circular-holes. At the same air-hole size and waveguide width, the PCW with the square holes can support higher bit rate of the signal up to 35 Gb/s. These results provide important theoretical basis for realizing of optical buffering and optical logic devices in all-optical network.     

Design and fabrication of two-dimensional photonic crystals with predetermined nonlinear optical properties

By probing the resonances between a photonic band and an external laser field and their nonlinear changes in angle-resolved reflectivity, we show experimental evidence that the nonlinear optical changes in a two-dimensional photonic crystal waveguide with a Kerr nonlinearity are critically dependent on the dispersion nature and the group velocity of the photonic bands. The results agree well with the behavior predicted from band structures, indicating that the design of nonlinear optical properties of material systems is realistically possible by band dispersion and group velocity engineering.     

The study of electro-optical sensor based on slotted photonic crystal waveguide

A compact and sensitive electro-optical sensor based on slotted photonic crystal waveguide (S-PhCW) is demonstrated. The electro-optical sensor can be realized in photonic crystal (PhC) slabs of silicon in Silicon-on-Insulator (SOI). Nonlinear optical polymer is used as infiltration. By applying three-dimensional finite difference time domain (3D-FDTD), the sensitivity and quality factor of electro-optical sensor with different slotted waveguide width are calculated. In addition, sensitivity and the optical properties such as transmission spectrum and field distributions are compared between electro-optical sensor based on line defect photonic crystal waveguide (W1-PhCW) and that based on slotted photonic crystal waveguide (S-PhCW). Simulation results demonstrate that, compared with electro-optical sensor based on line defect photonic crystal waveguide, the sensitivity and quality factor is improved by 30 times and 6.6 times respectively in sensor based on slotted photonic crystal waveguide. Besides, the proposed PhC sensor devices have the advantage of a compact structure with the potential for monolithic integration with optical-to-electrical on-chip conversion and detection.     

Photonic band gaps structure properties of two-dimensional function photonic crystals

The tunable two-dimensional photonic crystals band gap, absolute photonic band gap and semi-Dirac point are beneficial to designing the novel optical devices. In this paper, tunable photonic band gaps structure was realized by a new type two-dimensional function photonic crystals, which dielectric constants of medium columns are functions of space coordinates. However for the two-dimensional conventional photonic crystals the dielectric constant does not change with space coordinates. As the parameter adjustment, we found that the photonic band gaps structures are dielectric constant function coefficient, medium columns radius, dielectric constant function form period number and pump light intensity dependent, namely, the photonic band gaps position and width can be tuned. we also obtained absolute photonic band gaps and semi-Dirac point in the photonic band gaps structures of two-dimensional function photonic crystals. These results provide an important theoretical foundation for design novel optical devices.     

光子晶体线缺陷波导中的折射率相位移调制增强效应

在传统的基于全内反射原理的低折射率比介质波导所构建的相位移调制型光学器件中,调制区域的长度通常在毫米到厘米量级.由于器件横向尺寸保持在微米量级,因此狭长结构成为了传统光波导器件的典型特征,这限制了光学器件集成度的提高,严重制约了集成光路的进一步发展.光子晶体的出现为高密集成光路的发展提供了一条新的途径.本文使用平面波展开方法计算了光子晶体线缺陷波导中的色散曲线.研究发现:在色散曲线下边缘处,材料折射率的一个微小变化可以引起传输常数的较大变化,如果工作频率点选择在带下边缘附近,则可以大幅度减小相位移调制型器件调制区域的长度.本文使用时域有限差分方法进一步验证这种增强效应,计算结果表明,对于0.46%的折射率变化,光子晶体线缺陷波导中的相位调制长度仅为均匀媒质中相位移调制长度的11.7%.通过以进一步研究,这种增强效应有望应用与高密度集成光路.     

谐振腔侧边1×5介质柱调谐光子晶体滤波器

在正方格二维光子晶体结构中设计了基于可调谐谐振腔的带通滤波器,通过改变1×5谐振腔侧边调谐介质柱位置调节谐振腔与波导系统工作时传输的波段,用CMT理论分析了输入端耦合衰减率及输入端失谐因子对滤波器的影响。借助FDTD方法得到了滤波器波长传输谱,结果表明:当滤波器结构工作于1320~1810 nm波长段时,输出端38个通帯的-3 dB带宽Δλ范围为4.18~11.15 nm,通带峰值波长可调宽度为186.56 nm。该微型滤波器适于光电通信粗波分解复用WDDM系统设计和光集成设计等方面。     

Efficient coupler between chip-level and board-level optical waveguides

We propose an efficient optical coupler between a submicrometer-sized silicon waveguide on a silicon photonic chip and a multi-micrometer wide polymer waveguide on an optical printed circuit board for interchip optical networks. We show low coupling loss <0.4 dB with high lateral and angular tolerance to misalignment so that coupling can be done by automatic pick-and-place equipments with high throughput and low cost. The coupler has a wide optical bandwidth from 1470 to 1650 nm.     

Optical properties of one-dimensional photonic crystals obtained by micromatchining silicon (a review)

The theoretical and experimental investigations of photonic band gaps in one-dimensional photonic crystals created by micromatchining silicon, which have been performed by the author as part of his doctoral dissertation, are presented. The most important result of the work is the development of a method of modeling photonic crystals based on photonic band gap maps plotted in structure–property coordinates, which can be used with any optical materials and in any region of electromagnetic radiation, and also for nonperiodic structures. This method made it possible to realize the targeted control of the optical contrast of photonic crystals and to predict the optical properties of optical heterostructures and three-component and composite photonic crystals. The theoretical findings were experimentally implemented using methods of micromatchining silicon, which can be incorporated into modern technological lines for the production of microchips. In the IR spectra of a designed and a fabricated optical heterostructure (a composite photonic crystal), extended bands with high reflectivities were obtained. In a Si-based three-component photonic crystal, broad transmission bands and photonic band gaps in the middle IR region have been predicted and experimentally demonstrated for the first time. Si–liquid crystal periodic structures with electric-field tunable photonic band-gap edges have been investigated. The one-dimensional photonic crystals developed based on micromatchining silicon can serve as a basis for creating components of optical processors, as well as highly sensitive chemical and biological sensors in a wide region of the IR spectrum (from 1 to 20 μm) for lab-on-a-chip applications.     

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。     

点缺陷二维光子晶体波导的出射光集束

光子晶体器件在高密度集成光通信中有广泛的应用,为解决光子晶体波导出射光场的空间控制,采用时域有限差分法分析光子晶体波导结构的缺陷传播特性,提出基于点缺陷优化波导结构,通过在波导出射口两侧加上点缺陷,出射光方向性有显著提高,实现三点光源干涉系统的光集束。模拟结果表明缺陷态越靠近能带结构中央,共振腔的耦合效率越高;相反,缺陷态越靠近能带结构边缘位置,则共振腔耦合效率越低,因此,选取禁带区域四分之一处对应的点缺陷,可以有效实现波导出射的光集束。     

Analysis of optical characteristics of holey photonic crystal devices with the extended coupled-mode formalism

Presented here is a new approach for analysis of the so-called holey photonic crystals—a class of electro-optical components, in which periodicity of air holes in dielectric media is used for confinement of light. This class includes several kinds of microstructured fibers, semiconductor lasers etc. Accurate evaluation of optical characteristics of those devices is usually a complicated problem due to the large dimensions and the fine structure of their refractive index distribution. Furthermore, usually, only numerical solutions for this class of optical components are available. The overwhelming majority of the physical models, suitable for analysis of holey photonic devices, proceed from the “natural” assumption: the devices are considered as arrays of air holes, surrounded by dielectric material. In this work we propose another model. Namely, we treat them as arrays of dielectric spots (waveguides), embedded in the air (cladding material). This model allows utilization of the extended coupled-mode theory (a relatively new approach designed for analysis of infinite arrays of coupled waveguides and previously considered inapplicable to holey optical components) for calculations of the latter. In this sense, we present a new method for analysis of holey photonic crystals. On the one hand, our method allows analytical evaluation of some optical characteristics of holey optical components (such as the number of photonic bands and bandwidth). On the other hand, accurate numerical computation of the photonic band structure of the holey photonic devices, incorporating a large number of holes, can be done with this technique on a timescale of several minutes.