Influence of dielectrics with light absorption on the photonic bandgap of porous alumina photonic crystals

In this work, the influences of dielectrics with light absorption on the photonic bandgaps (PBGs) of porous alumina photonic crystals (PCs) were studied. Transmittance spectra of porous alumina PCs adsorbing ethanol showed that all the PBGs positions red-shifted; however, the transmittance of the PBG bottom showed different trends when the PBGs were located in different wavelength regions. In the near infrared region, liquid ethanol has strong light absorption, and, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs first increased and then decreased. However, in the visible light region, liquid ethanol has little light absorption, and thus, with the increase in adsorption, the PBG bottom transmittance of porous alumina PCs increased gradually all the time. Simulated results were consistent with the experimental results. The capillary condensation of organic vapors in the pores of porous alumina accounted for the change in the PBG bottom transmittance. The nonnegligible light absorption of the organic vapors was the cause of the decrease in the transmittance. The results for porous alumina PC adsorbing methanol, acetone, and toluene further confirmed the influences of light absorption on the PBG bottomed transmittance.

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Self-assembly route for photonic crystals with a bandgap in the visible region

Three-dimensional photonic crystals, or periodic materials, that do not allow the propagation of photons in all directions with a wavelength in the visible region have not been experimentally fabricated, despite there being several potential structures and the interesting applications and physics that this would lead to. We show using computer simulations that two structures that would enable a bandgap in the visible region, diamond and pyrochlore, can be self-assembled in one crystal structure from a binary colloidal dispersion. In our approach, these two structures are obtained as the large (Mg) and small (Cu) sphere components of the colloidal analogue of the MgCu(2) Laves phase, whose growth can be selected and directed using appropriate wall patterning. The method requires that the particles consist of different materials, so that one of them can be removed selectively after drying (for example, by burning or dissolution). Photonic calculations show that gaps appear at relatively low frequencies indicating that they are robust and open for modest contrast, enabling fabrication from more materials.     

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.     

Optical properties of a square-lattice photonic crystal within the partial bandgap

Optical properties of a two-dimensional square-lattice photonic crystal are systematically investigated within the partial bandgap through anisotropic characteristics analysis and numerical simulation of field pattern. Using the plane-wave expansion method and Hellmann-Feynman theorem, the relationships between the incident and refracted angles for both phase and group velocities are calculated to analyze light propagation from air to photonic crystals. Three kinds of flat slab focusing are summarized and demonstrated by numerical simulations using the multiple scattering method.     

Effect of photonic bandgap on upconversion emission in YbPO4:Er inverse opal photonic crystals

We obtained upconversion (UC) light-emitting photonic materials (YbPO(4):Er) with an inverse opal structure by the self-assembly technique in combination with a solgel method. The effect of the photonic stopband on the UC luminescence of the (2)H(11/2), (4)S(3/2)→(4)I(15/2), and (4)F(9/2)→(4)I(15/2) transitions of Er(3+) has been observed in the inverse opals of the Er(3+)-doped YbPO(4). Significant suppression of the UC emission was detected if the photonic bandgap overlapped with the Er(3+) ions emission band, while enhancement of the UC emission occurs if the emission band appears at the edge of the bandgap.     

二维旋转直柱光子晶体的频率带隙结构分析

设计了一种二维方形旋转正四边形直柱光子晶体,利用平面波展开方法计算了其光子频率带结构,发现在低频和高频区域,该类光子晶体的光子频率禁带明显增大.计算了空气中Al材料的旋转四边形直柱光子晶体的带结构和态密度,当填充比等于0.5时存在绝对带隙,旋转角度为45°时绝对带隙最大,旋转角度为0时,光子频率禁带位于高频区域.利用FDTD方法检验了计算结果,并分析了旋转角度为45°时,正四边形直柱光子晶体的波导特性以及TM模的电场分布.     

Characterization and study of photonic crystal fibres with bends

Analysis of a photonic crystal fibre (PCF) with bends is presented. Using the versatile finite difference time domain method, the modal characteristics of the PCFs are found. Possibilities of employing PCFs with bends in sensing are discussed. It is found that a large evanescent field is present when the bend angle exceeds 45°.     

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.     

Coated photonic crystals: computation of the Green tensor and analysis of the bandgap

A finite-size two-dimensional photonic crystal composed of dielectric rods with holes centered within each rod is considered. The geometry of the rods, as well as the holes, is of arbitrary shape. A boundary-element method is implemented for computing the Green tensor. The semi-analytical solution is used for validating the numerical results in the case of circular geometry. Different types of configurations and geometry shapes are considered in the computation.     

Omnidirectional reflection in several frequency ranges of one-dimensional photonic crystals

We investigate omnidirectional reflection from higher-order gaps in one-dimensional photonic crystals. Moreover, we present a designing criterion for omnidirectional reflection from several distinct gaps simultaneously, using only a single photonic crystal with a constant period. We show that for practical values of photonic crystals parameters, several relatively large omnidirectional gaps may be obtained. As an example, we demonstrate an omnidirectional reflector that exhibits two distinct wide omnidirectional ranges at near-infrared wavelengths. This omnidirectional reflector that operates in several ranges of wavelengths may have various potential applications.     

IR reflection spectra of NaCl crystals near a lattice resonance

This paper analyzes reflection spectra of NaCl crystals near an IR permittivity resonance. Dispersion laws, ω = ω(k), are derived for polariton waves. We calculate the velocity and effective mass of polaritons in different branches, compare theoretical results with a measured IR reflection spectrum reported earlier, and interpret the features observed in the reflection spectrum near the longitudinal optical phonon frequency.     

Optical thin-film reflection filters based on the theory of photonic crystals

Based on the theory of photonic crystals and the framework of a single-channel reflection filter that we presented before, structures of reflection filters with multiple channels are proposed. These structures can overcome some drawbacks of conventional multichannel transmission filters and are much easier to fabricate. We have practically fabricated the reflection filters with two and three channels, and the tested results show approximate agreement with theoretical simulation. Moreover, the superprism effect is also simulated in the single-channel reflection filter, the superiorities to transmission filters are discussed, and these analyses may shed some light on new applications of reflection filters in optical communication and other systems.     

All optical active high decoder using integrated 2D square lattice photonic crystals

The paper introduces a novel all optical active high 2 × 4 decoder based on 2D photonic crystals (PhC) of silicon rods with permittivity of ε = 10.1 × 10^?11 farad/m. The main structure of optical decoder is designed using a combination of five nonlinear photonic crystal ring resonator, set of T-type waveguide, and line defect of Y and T branch splitters. The proposed structure has two logic input ports, four output ports, and one bias input port. The total size of the proposed 2 × 4 decoder is equal to 40 μm × 38 μm. The PhC structure has a square lattice of silicon rod with refractive index of 3.39 in air. The overall design and the results are discussed through the realization and the numerically simulation to confirm its operation and feasibility.     

Colorimetric porous photonic bandgap sensors with integrated CMOS color detectors

In this paper, the development of a novel colorimetric sensor system based on the integration of complementary metal-oxide-semiconductor (CMOS) color detectors with a modified porous polymeric photonic bandgap sensor is reported. The color detector integrated circuit IC is implemented with AMI (AMI Semiconductor) 1.5 /spl mu/m technology, a standard CMOS fabrication process available at MOSIS (http://www.mosis.org). The color detectors are based on the spectral responses of buried double junctions (BDjs) and stacked triple junctions (STJs); the ratio of the photocurrents at the junctions provides spectral information. Both types of color detectors are characterized with a monochromator, and the results are compared. The BDJ color detector is used with a porous photonic bandgap reflection grating whose reflection spectra shifts as a function of the concentration of vapor analyte present. The experimental results verify that the color change of the photonic crystal can be detected and correlated to the change in analyte concentration. The entire system is compact and low power.     

空芯光子带隙光纤及其传感技术

本文综述了空芯光子带隙光纤的独特性质,并介绍了近年来这类光纤在传感领域应用的新进展。光波在空气纤芯中低损耗传输是空芯光子带隙光纤的重要特性,它带来了长距离、大能量密度的光与物质相互作用通道,降低了光纤材料属性对传输光的影响(如中红外吸收、热光效应),为诸如痕量气体/液体探测、高精度光纤陀螺仪等传感应用提供了高效的新平台。空芯光子带隙光纤内部精细的微结构具有新颖的机械性能和热性能,有利于诸如声波、振动探测等传感应用;还可结合光纤后期热处理、选择性填充等技术,对多孔包层进行结构修改或材料填充,获得进一步的性能和功能扩展。这些灵活性已用于开发具有新特性的光纤器件,例如光栅、起偏器和偏振干涉仪。目前,空芯光子带隙光纤传感技术的发展已大大扩展了光纤的环境感知能力和应用范围,是全光器件和光集成技术发展的重要方向。

     

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.     

Manipulating wavelength-selective emission with heterogeneous photonic crystals

The usual near-field radiation profile of a light beam emanating from a photonic crystal waveguide (PCW) has a main lobe at the center line of the waveguide. However, a centrally symmetric profile for the emission pattern with two sidelobes can be required in some applications, e.g., Y-type power dividers, wavelength multiplexers, and semiconductor lasers. With such motivations in mind, we present the design of a compact structure that deflects the beam propagation direction in this manner. The idea utilizes the manipulation of the dispersion diagram of cascaded photonic crystals by exploiting the bandgap and self-collimation properties. The waveguide mode in the PCW can be transformed from a propagating mode into a diffusive one by altering the filling factor, which, in turn, leads to off-axis light emission. By using the finite-difference time-domain method, we show that the emission takes place into free space at the inclined output surfaces of the PCW with deviation angles of ±45°.