Arbitrary angle waveguide bends based on zero-index metamaterials

In this paper, efficient arbitrary angle bends based on impedance-matched zero-index metamaterials (ZIMs) are proposed. Numerical simulations on ZIM-based bends are carried out in waveguide systems. The results show clearly that electromagnetic waves can tunnel through the ZIM-based bends with high transmittance at any bending angles. Moreover, a realistic ZIM-based bends are designed and fabricated on microstrip transmission line. Both simulated and experimental results confirm well the low loss and arbitrary angle bending effects in a system hiring ZIM-based microstrip ring resonator as bending corners.     

Optimization of T-shaped waveguide branches in two-dimensional photonic crystals

The interval and the radius of a pair of defect dielectric rods in waveguide channels near the branching region of a T-shaped waveguide branches are simultaneously varied, and their effects on the transmission properties are investigated using the finite-difference time-domain (FDTD) method. Numerical results show that there is an optimized region where the relative bandwidth of high-transmission (total transmittance 0.95) band of the branches is larger than 17%, which is higher than that of the existing same structures (11.60%) with fixed interval. These results provide for engineering application of simple T-shaped waveguide branches with high transmission.     

Silica glass bend waveguide assisted by two-dimensional photonic crystals

In this paper we report on the modeling of low index contrast silica glass 90° bend ridge waveguides assisted by a two-dimensional photonic crystal. A three-dimensional finite-difference time-domain (3D-FDTD) based computer code has been used in order to evaluate the transmission characteristics and the in-plane losses of the investigated waveguides having different values of the bend radius. The performance of the bend structure surrounded by two-dimensional photonic crystals is compared to that of a classical bend ridge waveguide and the phenomenon of light confinement is critically analyzed. The device design is optimized for quasi-TM polarization at the wavelength of 1.3 μm.     

二维光子晶体T型波导分支器数值模拟研究

采用平面波展开法和时域有限差分法,对GaAs二维正方晶格光子晶体的色散特性和带隙结构进行了数值模拟研究,并对GaAs二维光子晶体线缺陷构成的T型波导分支器的微波传输特性进行了模拟和优化。数值模拟结果表明,光子晶体填充比对带隙结构有显著地影响。通过在拐角处插入额外的电介质棒对GaAs二维正方光子晶体T型波导分支器进行优化,数值模拟的结果表明,优化的GaAs二维正方光子晶体T型波导分支器在一阶带隙范围内透射系数将提高到0.96以上。     

Ultracompact waveguide bends with simple topology in two-dimensional photonic crystal slabs for optical communication wavelengths

Ultracompact waveguide bends with simple topology in two-dimensional photonic crystal slabs are proposed by using an annular air groove at the bend corner to improve transmissions of the bends. Analysis indicates that the guided light wave experiences a very slight difference of propagation properties between straight waveguides and bends (with 60 degrees and 120 degrees bending angles). Transmissions of more than 90% can be achieved in the 60 degrees and 120 degrees bends for light waves at 1.55 microm with bandwidths of 101 and 74 nm, respectively.     

Improved bends for two-dimensional photonic crystal waveguides

For two-dimensional photonic crystals involving infinitely long dielectric rods or air-holes on square or triangular lattices, a number of high performance 60° and 90° waveguide bends are obtained by solving optimization problems involving the radii of a few rods or air-holes as the degrees of freedom. In particular, the proposed 60° bends significantly outperform previous designs that insert three or five identical air-holes in the bend. The optimization problems are solved using a recently developed method based on the so-called Dirichlet-to-Neumann (DtN) maps of the unit cells.     

Arbitrary structuring of two-dimensional photonic crystals by use of phase-only Fourier gratings

The computer-generated holography technique is applied to the structuring of two-dimensional (2D) photonic crystals with inherently embedded arbitrary defects. The technique uses phase-only Fourier gratings as a generator of spot arrays in the focal plane, such that a single exposure produces a 2D array of focused spots with desired defects or modifications in the lattice structure. We demonstrate several types of large-area 2D lattice structures with square, hexagonal, or hybrid lattices embedded with point and (or) line defects. Scanning the Fourier plane in the depth direction throughout multiphoton polymerization media allows 3D lattices with stacked defect layers to be formed.     

Low-dimensional waveguide microwave photonic crystals

Structures containing periodically alternating elements, which are a source of high-order waves, are investigated as low-dimensional waveguide microwave photonic crystals. The band character of the transmittance and the reflectance of a photonic crystal, which consists of sequentially alternating dielectric layers and thin metallic plates partially overlapping the waveguide section, is revealed by the numerical modeling and the experimental investigation of amplitude-frequency characteristics. It has been shown that the application of metallic plates with gaps in the structure of the photonic crystal made it possible to decrease its longitudinal size substantially compared with photonic crystals fabricated based on elements made of alternating dielectric layers with various permittivities.     

Transmission of slow light through photonic crystal waveguide bends

The spectral dependence of the bending loss of cascaded 60 degrees bends in photonic crystal (PhC) waveguides is explored in a slab-type silicon-on-insulator system. An ultralow bending loss of (0.05 +/- 0.03) dB/bend is measured at wavelengths corresponding to the nearly dispersionless transmission regime. In contrast, the PhC bend is found to become completely opaque for wavelengths corresponding to the slow-light regime. A general strategy is presented and experimentally verified to optimize the bend design for improved slow-light transmission.     

Polarization-independent self-collimating bends and beam splitters in photonic crystals

Polarization independent bends and beam splitters for transverse electric (TE) and transverse magnetic (TM) polarizations have been demonstrated in two-dimensional (2D) photonic crystals (PhCs). In virtuel of equi-frequency contour analysis and finite-difference time-domain calculations, self-collimation behaviors for TE- and TM-polarizations are achieved at the same frequency. Simulation results show a 90-degree bend with 90% efficiency and beam splitters with about 96% total efficiency for both TE- and TMpolarizations, where the light is self-guided by the self-collimation effect. Such bends and beam splitters are expected to play important roles in optical devices where polarization insensitivity is needed.     

The single-longitudinal-mode operation of a ridge waveguide laser based on two-dimensional photonic crystals

An electrically driven, single-longitudinal-mode GaAs based photonic crystal (PC) ridge waveguide (RWG) laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic is achieved by introducing the PC to the RWG laser. The triangle PC is etched on both sides of the ridge by photolithography and inductive coupled plasma (ICP) etching. The lasing spectra of the RWG lasers with and without the PC are studied, and the result shows that the PC purifies the longitudinal mode. The power per facet versus current and current-voltage characteristics have also been studied and compared.     

慢光在光子晶体弯折波导中的高透射传播

研究了慢光模式在SOI(silicon-on-insulator)材料光子晶体线缺陷弯折波导中的传输特性. 通过优化波导弯折处的结构参数,慢光模式在光子晶体60°与120°弯折波导中的透射率提高10倍以上,归一化透射率分别达到80%和60%以上. 为了进一步减慢光速,设计了新颖的高Q值耦合腔弯折波导结构,在归一化透射率达到75%的基础上,光波群速度低至c/170(c为真空光速). 研究结果对于增强光子晶体的慢光效应,提高光子晶体慢光器件的微型化和集成化都有一定的积 关键词： 光子晶体 慢光 弯折波导 透射率     

Magneto-optical defects in two-dimensional photonic crystals

We analyze the properties of magneto-optical defect states in two-dimensional photonic crystals. With out-of-plane magnetization, the magneto-optical coupling splits doubly-degenerate TE states into two counter-rotating modes at different frequencies. The strength of magneto-optical coupling strongly depends on the spatial overlap of the cavity domain structures and the cross product of the modal fields. The transport property of the resultant nonreciprocal states is demonstrated in a junction circulator structure with a magneto-optical cavity coupled to three waveguides. By a proper matching of the magneto-optical frequency splitting with the cavity decay rate into the waveguide, ideal three-port circulator characteristics with complete isolation and transmission can be achieved, with an operational bandwidth proportional to the magneto-optical constant. The proposed optical circulator in a bismuth-iron-garnet/air photonic crystal is demonstrated with finite-difference time-domain calculations and is compared to an alternative implementation of silicon/air crystal infiltrated with a single bismuth-iron-garnet domain.     

Diffraction inhibition in two-dimensional photonic crystals

We show the existence of flat equal-frequency contour across the entire first Brillouin zone in two-dimensional photonic crystals. Under this condition, light diffraction can be inhibited. Moreover, the beam can be highly localized between two neighboring rows of the defect-free photonic crystal. Such a finding may have novel applications in light beam manipulations and on-chip integrated photonic devices.     

Negative refraction in two-dimensional photonic crystals

We present some of our recent results for negative refraction in photonic crystals. The concept of negative refraction in photonic crystals is firstly introduced. Then, the propagation of electromagnetic waves in photonic crystals is systematically studied. By the layer Korringa–Kohn–Rostoker method, the coupling efficiency between external plane waves and the Bloch waves in photonic crystals is investigated. It is found that the coupling coefficient is highly angular dependent even for an interface between air with n=1 and a photonic crystal with effective index n_eff=-1. It is also shown that, for point imaging by a photonic crystal slab, owing to the negative refraction, the influence of the surface termination on the transmission and the imaging quality is significant. Finally, we present results experimentally demonstrating negative refraction in a two-dimensional photonic crystal at optical communication wavelengths. PACS 42.70.Qs; 41.85.Ct; 42.30.Va     

Terahertz two-dimensional high-Q photonic crystal waveguide cavities

Numerical simulations were used to design a variety of high-Q resonant cavities for integration into a terahertz 2D photonic crystal waveguide. After fabrication, the transmission characteristics of each integrated cavity were explored. These photonic waveguide-coupled cavities demonstrate resonances with linewidths approaching 10 GHz. The results compare favorably to previous observations of rectangular waveguide cavities. Good agreement between the experimental results and the numerical simulations was obtained.     

Superbending effect in two-dimensional graded photonic crystals

We study the superbending effect in a two-dimensional graded photonic crystal (GPC) for both TE and TM modes. We show that the lateral beam shift is extremely sensitive to the wavelength for the TM mode but not TE mode, indicating the potential in designing some special superbending devices, for example, TE/TM splitter and polarization-indifference waveguide at prescribed wavelengths.     

Archimedes 32,4,3,4结构光子晶体中与偏振无关的自准直分束器

通过等频图分析并结合时域有限差分法法模拟, 在Archimedes 3²,4,3,4结构排列的二维光子晶体中同一频率下同时实现了电磁波两种偏振态的自准直. 研究发现,在该结构光子晶体中引入缺陷,当线缺陷宽度改变时, TE和TM两种偏振态光束的分束效果将会随之变化.由此通过控制缺陷宽度,分别实现了两种偏振态光束的50% ∶50%分束以及90°大角度光折弯,分束和折弯的效率都较为理想,为未来设计基于光子晶体的新型光子学器件提供了一种新的思路.     

Optical circulators in two-dimensional magneto-optical photonic crystals

We propose an optical circulator formed of a magneto-optical cavity in a 2D photonic crystal. With spatially engineered magnetic domain structures, the cavity can be designed to support a pair of counterrotating states at different frequencies. By coupling the cavity to three waveguides, and by proper matching of the frequency split of the cavity modes with the coupling strength between the cavity and the waveguide, ideal three-port circulators with complete isolation and transmission can be created. We present a guideline for domain design needed to maximize the modal coupling and the operational bandwidth for any given magneto-optical constant.     

Band-edge-induced Bragg diffraction in two-dimensional photonic crystals

Two-dimensional photonic crystals composed of two orthogonal volume diffraction gratings have been photogenerated in photopolymers. When the read beam is set at the Bragg angle, the diffraction efficiency of the transmission grating is strongly enhanced at the band edge of the reflection grating recorded in the material. Such a device provides Bragg operation and enhancement of the diffraction efficiency of the thin diffraction grating together with good wavelength selectivity. Such advantages could be interesting for optical signal processing.