Optical interleavers based on two-dimensional photonic crystals

An ultrasmall device size optical interleaver based on directional coupler waveguides in two-dimensional photonic crystals (PCs) is proposed. The numerical results show that the proposed PCs waveguide structure could really function as an interleaver with the central wavelength 1550 nm and the channel spacing 0.8 nm (frequency spacing of 100 GHz) of the dense wavelength division multiplexing (DWDM) specification. It can be widely used as the wavelength selective element for multiplexer-demultiplexer to lower or raise channel densities in DWDM optical fiber communication systems.     

Negative refraction in two-dimensional photonic crystals

A two-dimensional, square-lattice photonic crystal model possessing analytical solutions is investigated to ascertain the requirements for negative refraction to occur. The refraction properties are presented for both polarizations assuming in-plane propagation and phase matching conditions across a surface perpendicular to the ΓM-direction of the crystal. It is shown that the most isotropic and highest effective refractive index is obtained near the maximum of the lowest band for a crystal with a high refractive index contrast between its constituent materials.     

Acousto-optic efficiency of two-dimensional photonic crystals

The Bragg regime of the acousto-optic (AO) interaction in two-dimensional (2D) photonic crystals (PhCs) is considered. Approximate formulas for the AO figures of merit of PhCs are obtained and their frequency dependences for 2D PhC of the Si-SiO₂ system are calculated. It is shown that the figures of merit of a composite PhC can exceed the values of these parameters for the components.     

Resonance properties of two-dimensional photonic crystals

The resonance properties of two-dimensional photonic crystals, which are manifested by the localization of radiation inside these objects at frequencies corresponding to their bandgap boundaries, have been theoretically studied. This effect is compared to resonances in photonic crystals with violated internal structure, which are related to the generation of defect modes.     

Photonic crystals and photonic structures

This paper reviews the state-of-the-art of photonic band gap materials, addressing separately the spectral ranges of microwaves and optics. In the microwave domain, applications seem to emerge in particular, thanks to the recent breakthrough of metallo-dielectric structures. In the optical domain, 3D structures have been recently demonstrated in the infrared. In the mean time, refractive index engineering of a variety of complex structures involving photonic band gap reflections as well as more classical Fresnel confinement of light is now underway for the study of quantum electrodynamics in the solid state.     

Beam splitter and beam bends based on self-collimation effect in two-dimensional photonic crystals

Basing on the self-collimation effect of photonic crystals, one-to-two beam splitter, beam bend and one-to-three beam splitter are, respectively, designed by introducing a different line defect along the same direction. From the equal-frequency contour plot which is calculated by the plane wave expansion method, we obtain the frequency and the propagate direction of the self-collimated beam. The self-collimated beam propagation in photonic crystals with different line defects is simulated by the two-dimensional finite-difference time-domain method with perfectly matched layer absorbing boundary conditions. The simulation results show that one-to-two beam splitter, beam bend and one-to-three beam splitter can be realized by appropriately arranging the line defect along the proper direction. Such devices can greatly enhance photonic crystals for use in high-density optical integrated circuits.     

Symmetry properties of two-dimensional anisotropic photonic crystals

A theoretical study of two-dimensional photonic crystals made of anisotropic material is presented. Detailed computation principles including a treatment of the TE and TM polarizations are given for a photonic crystal made of either uniaxially or biaxially anisotropic materials. These two polarizations can be decoupled as long as any one of the principal axes of the anisotropic material is perpendicular to the periodic plane of the photonic crystal. The symmetry loss due to the anisotropy of the material and the variation of the Brillouin zones relative to the tensor orientations are also analyzed. Furthermore, the symmetry properties of the two-dimensional photonic band structure are studied, and the resulting effect on the photonic bandgap and the dispersion properties of photonic crystal are analyzed as a function of the orientation of the anisotropic material.     

Nonlinear optical responses in two-dimensional photonic crystals

A two-dimensional (2D) highly nonlinear lithium niobate (LN) photonic crystal (PhC) waveguide is fabricated with the aim of studying its nonlinear optical properties. We show a large enhancement of the second-harmonic generation (SHG) in the 2D LN PhCs, originating from resonance between the external pump laser field and a photonic band mode. The SHG enhancement results agree well with the experimental photonic band structure obtained by an angle-dependent optical reflectivity and the theoretical band structure generated by three-dimensional finite-difference time-domain calculations. These results open new possibilities for the use of 2D LN PhC waveguide in integrated nonlinear optical applications.     

Equal-frequency surface analysis of two-dimensional photonic crystals

This paper presents an analytical treatment of equal-frequency surface analysis of a two-dimensional photonic crystal. We first define the equal-frequency surface in terms of plane waves, which can be numerically evaluated. Then one- and two-plane-wave approximations are proposed, which consequently lead to analytical expressions of the equal-frequency surface. The approach presented is well suited to two-dimensional photonic crystals of weak dielectric modulation. For photonic crystals with a large modulation, the approach can be used to gain a general idea of the shape of the bands.     

Tuning the flow of light in two-dimensional metallic photonic crystals based on Faraday effect

In this paper, we investigate the tunability of two-dimensional metallic photonic crystals by an external magnetic field. Our theoretical analysis is based on the frequency-dependent plane wave expansion method. The numerical results show that the external magnetic field has a pronounced effect on the permittivity of the metals. Therefore, the photonic band structures can be strongly tuned and controlled by adjusting the external magnetic field. Our structure is a good candidate for many applications such as filters, optical switches and modulators.     

All-optical controllable channel-drop filters in two-dimensional square-lattice photonic crystals

A novel all-optical controllable channel-drop filter in photonic crystals (PC) of square lattice is presented. We show that using a resonant-cavity-based add-drop filter with a wavelength-selective reflection feedback and a single-control switching module which is based on nonlinear PC microcavities, the dropped channel can be routed to the drop port or returned to the bus waveguide. Using the temporal coupled-mode theory and two-dimensional nonlinear finite-difference time-domain method, the performance of the proposed device is investigated and the simulation results show the validity of the proposed design.     

Channel drop filter in two-dimensional triangular lattice photonic crystals

Based on two-dimensional photonic crystals with a triangular lattice, a channel drop filter with a wavelength-selective reflection microcavity is designed. In the structure, two microcavities are used. One is used for a resonant tunneling-based channel drop operation. The other is used to realize wavelength-selective reflection feedback in the bus waveguide. The phase term, which is derived by means of coupled-mode theory to achieve close to 100% drop efficiency, is satisfied by modifying the sizes of the border air holes next to the bus waveguide section between the two cavities. Using the finite-difference time-domain method, the simulation results show complete power transfer between the bus and drop waveguides via the system.     

Computing equifrequency contours of two-dimensional photonic crystals by Dirichlet-to-Neumann maps

Equifrequency contours provide important information for designing special photonic crystal devices. In this paper, we present an efficient method to compute equifrequency contours for two-dimensional photonic crystals with triangular and honeycomb lattices. Our method is based on the Dirichlet-to-Neumann (DtN) operator of a unit cell in the photonic crystal. The DtN operator maps the wave field on the boundary of the unit cell to its normal derivatives. For photonic crystals with a triangular or honeycomb lattice, a small linear eigenvalue problem is formulated to calculate the dispersion relation. The formulation is based on the DtN map of the unit cell for a given angular frequency, and the eigenvalue is related to the wave vector. Our method is especially suitable for calculating the equifrequency contours, if a relatively small number of frequencies are involved.     

Properties of two-dimensional photonic crystals with octagonal quasicrystalline unit cells

The bandstructures of two-dimensional photonic crystals with octagonal quasicrystalline unit cells have been calculated. The existence of photonic band-gaps in such structures is demonstrated, and results showing the variation of the spectral position and width of the photonic band-gaps with the size of the unit cell and filling fraction within the unit cell are presented.     

Single-beam holography for Ag nanoparticle-embedded two-dimensional binary metallodielectric photonic crystals

Absolute photonic bandgaps of photonic crystals can be increased by reducing the structural symmetry and/or by enhancing the refractive index contrast. We have experimentally demonstrated a single-beam holography for creating Ag nanoparticle-embedded 2D binary photonic microstructures by adding a different diameter rod in the center of each original 2D honeycomb lattice for simultaneously realizing both symmetry reduction and the enhancement of the index contrast of PC structures.     

The properties of cutoff frequency in two-dimensional superconductor photonic crystals

In this paper, by means of frequency-dependent plane wave expansion method we investigate the properties of photonic band structures in two-dimensional superconductor photonic crystals. Effects of cut-off frequency are investigated by various parameters such as filling factor, the lattice constant alteration, threshold frequency of the superconductor, and shape of the rods as well. We show that the cut-off frequency can be efficiently tuned by the operating temperature. Moreover, it can be tailored by changing the dielectric constant of the background and the threshold frequency of the superconductor material.     

基于声子晶体的车内噪声研究

声子晶体是近年来提出的一种新型功能材料,是一种由两种或多种材料组成的具有周期性结构和弹性波带隙的声学功能材料或结构,并且振动频率在声子晶体带隙范围内的振动会被抑制或禁止传播,它所具有的这种弹性波带隙特性为汽车车内噪声控制,特别是车内低频噪声控制提供了一种新的研究方法.在介绍了声子晶体的概念、基本特征及能带结构的基础上,阐述了声子晶体在振动与噪声控制领域的研究现状,同时对车内噪声的产生机理进行了分析,最后对声子晶体在应用于汽车车内降噪方面的研究做了展望.     

Metallic photonic crystals based on solution-processible gold nanoparticles

We demonstrate the fabrication of metallic photonic crystals, in the form of a periodic array of gold nanowires on a waveguide, by spin-coating a colloidal gold suspension onto a photoresist mask and subsequent annealing. The photoresist mask with a period below 500 nm is manufactured by interference lithography on an indium tin oxide (ITO) glass substrate, where the ITO layer has a thickness around 210 nm and acts as the waveguide. The width of the nanowires can be controlled from 100 to 300 nm by changing the duty cycle of the mask. During evaporation of solvent, the gold nanoparticles are drawn to the grooves of the grating with apparently complete dewetting off the photoresist for channels less than 2 microm in width, which therefore form nanowires after the annealing process. Strong coupling between the waveguide mode and the plasmon resonance of the nanowires, which is dependent on the polarization and incidence angle of the light wave, is demonstrated by optical extinction measurements. Continuity of the nanowires is confirmed by conductivity properties. Simplicity, high processing speed, and low cost are the main advantages of this method, which may have a plethora of applications in telecommunication, all-optical switching, sensors, and semiconductor devices.     

Simulation of two-dimensional Kerr photonic crystals via fast Fourier factorization

We present an adaptation of the fast Fourier factorization method to the simulation of two-dimensional (2D) photonic crystals with a third-order nonlinearity. The algorithm and its performance are detailed and illustrated via the simulation of a Kerr 2D photonic crystal. A change in the transmission spectrum at high intensity is observed. We explain why the change does not reduce to a translation (redshift) but rather consists in a deformation and why one side of the bandgap is more suited to a switching application than the other one.     

Gallium nitride based logpile photonic crystals

We demonstrate a nine-layer logpile three-dimensional photonic crystal (3DPC) composed of single crystalline gallium nitride (GaN) nanorods, ～100 nm in size with lattice constants of 260, 280, and 300 nm with photonic band gap in the visible region. This unique GaN structure is created through a combined approach of a layer-by-layer template fabrication technique and selective metal organic chemical vapor deposition (MOCVD). These GaN 3DPC exhibit a stacking direction band gap characterized by strong optical reflectance between 380 and 500 nm. By introducing a "line-defect" cavity in the fifth (middle) layer of the 3DPC, a localized transmission mode with a quality factor of 25-30 is also observed within the photonic band gap. The realization of a group III nitride 3DPC with uniform features and a band gap at wavelengths in the visible region is an important step toward realizing complete control of the electromagnetic environment for group III nitride based optoelectronic devices.