Enhanced beaming of light from a photonic crystal waveguide via a self-collimation photonic crystal

A simple method to control the light transmission from a photonic crystal waveguide (PCW) is proposed. The self-collimation (SC) effect in PC is utilized to depress the diffractive behavior of the light beam emitting out from the PCW. The finite difference in time domain (FDTD) simulation results show that choosing appropriate self-collimation frequency and the space between the PCW and the SC-PC can achieve a very good collimating beam in the outgoing side.     

Conditions for self-collimation in three-dimensional photonic crystals

We introduce the theoretical criterion for achieving three-dimensional self-collimation of light in a photonic crystal. Based on this criterion, we numerically demonstrate a body-center-cubic structure that supports wide-angle self-collimation and is directly compatible with the recently developed holographic fabrication technique. We further show that both bends and beam splitters can be introduced into this structure by the use of interfaces.     

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.     

Broadband large-angle self-collimation in two-dimensional silicon photonic crystal

We report a two-dimensional silicon photonic crystal structure that supports the self-collimation effect with large incident angles over a broad wavelength range. We theoretically and experimentally show the propagation light in the designed and fabricated structure without diffraction. Broadband large-angle self-collimation is observed in infrared wavelength.     

Controlling the self-collimation characteristics of a near-infrared two-dimensional metallic photonic crystal

Self-collimation characteristics of the two-dimensional square-lattice photonic crystal(PC) consisting of metal rods immersed in silicon are studied by the finite-difference time-domain method.The Drude dispersion model is adopted to describe the metal rod,and the self-collimation behaviours of the near-infrared light through the PC are studied.The frequency region and the tolerance of incident angle for the self-collimation behaviour can be controlled by changing the shape of the metal rods.     

Polarization beam splitter based on photonic crystal self-collimation Mach-Zehnder interferometer

A polarization beam splitter based on a self-collimation Mach-Zehnder interferometer (SMZI) in a hole-type silicon photonic crystal was proposed and numerically demonstrated. Utilizing polarization dependence of the transmission spectra of the SMZI and polarization peak matching (PPM) method, the SMZI can work as a polarization beam splitter (PBS) by selecting appropriate path length difference in the structure. Because of its intrinsic operating principle, the PBS possesses high polarization extinction ratios (PERs). As its dimensions are only several operating wavelengths, the PBS may have practical applications in photonic integrated circuits.     

Experimental demonstration of super quasi-phase matching in nonlinear photonic crystal

We have demonstrated super quasi-phase matching (QPM) in a super periodically poled lithium niobate (PPLN), which is composed of multiple ordinary PPLN cells. When super QPM is achieved, the slight phase mismatch in each PPLN cell can be further compensated for, and the relevant second harmonic generation is facilitated greatly. This mechanism provides an insightful means to relieve the limitation imposed by sample fabrication inaccuracy and will open up a promising avenue toward highly efficient nonlinear interactions.     

Wavelength-division-multiplexing system with photonic crystal self-collimation and co-directional coupling effect

A wavelength-division-multiplexing system with high compactness and extremely simple structures is designed and analyzed theoretically for optical communication wavelengths. The structure consists of a self-collimation region, a coupler, a coupling section, and two arbitrarily bent periodic dielectric waveguides (PDWGs). Operation principle of the devices is based on self-collimation and directional coupling mechanism. The equal-frequency contours (EFCs) are nearly flat from 0.17–0.22 (2πc/a), thus the self-collimation region acts as a multiplexer. Operation principle of the demultiplexer is based on directional coupling in two parallel periodic dielectric waveguides. The device performances have been evaluated by the finite-difference time-domain simulations coupled with perfectly matched layer (PML) boundary conditions.     

基于自准直效应的光子晶体异质结偏振分束器

基于光子晶体的自准直效应和禁带特性,提出了一种具有非正交异质结结构的光子晶体偏振分束器.无需引入缺陷或波导,可使光波在该结构中准直无发散地传输并实现分束功能,对制造工艺的要求大大降低.利用Rsoft软件,结合平面波展开法和二维时域有限差分法,对提出的偏振分束器进行了仿真研究.结果表明,该偏振分束器在一个较大的频率范围f=0.275—0.285(a/λ)内可实现横电(TE)和横磁(TM)模的大角度偏振分离,TE和TM模的透过率均在88%以上,偏振消光比分别大于26.57 dB和17.50 dB.该结构可应用到太赫兹波段的传输系统中,a=26μm,尺寸大小为572μm×546μm,在91—95μm波长范围内可实现TE和TM模的分离.利用该结构可设计用于光通信系统(n=3.48)的偏振分束器,a=426.25 nm,结构仅为9.38μm×8.95μm.本方案结构简单,易于集成,有望在集成光路的发展中发挥重要作用.     

Photonic drop splitters based on self-collimation ring resonators in a silicon photonic crystal

We report here 1 × 3 and 1 × 2 photonic drop splitters (PDSs) with different splitting ratios based on self-collimation ring resonators (SCRRs) in an air-hole silicon photonic crystal. An 1 × 3 PDS consists of four beam splitters and an 1 × 2 PDS consists of three beam splitters and one mirror. Light propagates in the PDSs employing self-collimation effect. The theoretical transmission spectra at different drop ports in PDSs were analyzed with the multiple-beam interference theory. Then they were investigated with the finite-difference time-domain (FDTD) simulation technique. The simulation results agree well with the theoretical prediction. For the drop wavelength 1550 nm, the free spectral range of the PDSs is about 29 nm, which almost covers the whole optical communication C-band window. Because of small dimensions, air-hole structure and whole-silicon material, the proposed PDSs hold great potentials for applications in photonic integrated circuits.     

基于光子晶体自准直环形谐振腔的全光均分束器

通过等频图分析并结合时域有限差分法模拟,在一个与偏振态无关的自准直光子晶体环形谐振腔中,研究发现当环形谐振腔内的光传输距离改变时,横电波(TE)和横磁波(TM)两种偏振态的光在通过环形谐振腔之后的输出将会随之变化并呈现出不同的周期性.通过选择适合的传输距离,实现了TE,TM自准直的情况下同时分束50%的结果,构成了一种基于光子晶体自准直环形谐振腔的全光均分束器.全光均分束器扩大了分束器的运用范围,也会在高密度集成光路中发挥重要的作用. 关键词： 光子晶体 环形谐振腔 自准直 分束器     

Extraordinary wavelength dependence of self-collimation effect in photonic crystal with low structural symmetry

We present the optical properties of a new type of photonic crystal (PC) named star-shaped PC (STAR-PC) with anomalous equi-frequency contours. Intentionally introducing low-symmetry in the primitive unit cell gives rise to progressively tilting flat contours, which are observed in the fifth band of the transverse magnetic mode. Due to the intrinsic dispersive feature of the proposed PCs, i.e. tilted self-collimation, the incident signal with different wavelengths can be successfully separated in a spatial domain without introducing any corrugations or complexities inside the structure. We show numerical investigations of wavelength selective characteristic of the proposed PC structure in both time and frequency domains. The STAR-PC approach can be considered a good candidate for the wavelength division applications in the design of compact photonic integrated circuits. For the purpose of wavelength separation implementations, the proposed structure may operate within the wavelength interval of 1484.5–1621.5 nm with a broad bandwidth of 8.82%. The corresponding inter-channel crosstalk value is as low as ?19 dB and the calculated transmission efficiency is above 97%.     

Experimental demonstration of 1535-1555-nm simultaneous optical wavelength interchange with a nonlinear photonic crystal

We present results of what is to our knowledge the first experimental demonstration of simultaneous optical wavelength interchange by use of a two-dimensional second-order nonlinear photonic crystal. Fabrication and performance parameters of a 1535-1555-nm wavelength interchange nonlinear photonic crystal fabricated in lithium niobate are discussed.     

Fabrication of high-quality three-dimensional photonic crystal heterostructures

Three-dimensional photonic crystal (PC) heterostructures with high quality are fabricated by using a pressure controlled isothermal heating vertical deposition technique. The formed heterostructures have higher quality, such as deeper band gaps and sharper band edges, than the heterostructures reported so far. Such a significant improvement in quality is due to the introduction of a thin TiO₂ buffer layer between the two constitutional PCs. It is revealed that the disorder caused by lattice mismatch is successfully removed if the buffer layer is used once. As a result, the formed heterostructures possess the main features in the band gap of constitutional PCs. The crucial role of the thin buffer layer is also verified by numerical simulations based on the finite-difference time-domain technique.     

Modified spontaneous emission of CdTe quantum dots inside a photonic crystal

The angular dependence of the spontaneous emission of CdTe quantum dots (QDs) inside a photonic crystal with a pseudogap is reported. The sensitive dependences of the radiative lifetime and the photoluminescence spectrum of CdTe QDs on the observation angle demonstrate the effect of the photonic bandgap on the spontaneous emission of the QDs.     

Extremely high transmission of light through a nanohole inside a photonic crystal

The transmission of light through single nanoholes with diameters considerably smaller than the wavelength of light (smaller than ??/10) is experimentally studied. The nanoholes were made in a gold film, which is a part of a photonic crystal forming a microcavity with the quality factor Q ?? 100. A 28-fold increase in the transmission of light through a nanohole inside the microcavity compared to transmission through a nanohole in a gold film is demonstrated. The high spectral selectivity of light transmission through a nanohole is discovered, which is characterized by two features: (i) the transmission maximum is located at the resonance wavelength of the microcavity and (ii) the peak full width at half-maximum is about ??/90.     

Design for directional emitter based on self-collimation photonic crystal by adding two-layer dielectric rods

We propose a novel directional emitter for achieving highly efficient beaming of self-collimated light from two-dimensional photonic crystal (PC). The structure is composed of a two-dimensional (2D) photonic crystal and two-layer dielectric rods. The finite-difference time-domain (FDTD) simulations show that the emission properties are sensitive to the distance between photonic crystal and two-layer dielectric rods. By adjusting the relative position of the two-layer dielectric rods, highly efficient beaming emission can be realized.     

Optical properties of a three-dimensional silicon square spiral photonic crystal

We report the fabrication and optical characterization of a tetragonal square spiral photonic crystal with a three-dimensional relative band gap of approximately 10% using the glancing angle deposition (GLAD) technique. This thin film structure is produced in a one-step process that is highly versatile as a wide range of crystal structures can be created simply through the variation of deposition parameters. Measurements indicate upper and lower frequency band edges at vacuum wavelengths of 2.50 and 2.75 μm, in the infrared region of the spectrum.     

High-efficiency calculations for three-dimensional photonic crystal cavities

A numerical method was developed by combining a plane-wave-based transfer matrix method and a robust rational function interpolation algorithm. The optical properties of three-dimensional photonic crystal cavities were extracted in a short computation time with high numerical accuracy.     

Butterfly wing color: A photonic crystal demonstration

We have theoretically modeled the optical behavior of a natural occurring photonic crystal, as defined by the geometrical characteristics of the Teinopalpus Imperialis butterfly. In particular, following a genetic algorithm approach, we demonstrate how its wings follow a triclinic crystal geometry with a tetrahedron unit base. By performing both photonic band analysis and transmission/reflection simulations, we are able to explain the characteristic colors emerging by the butterfly wings, thus confirming their crystal form.