Optical diodes and omnidirectional reflectors based on one-dimensional quasiperiodic photonic crystals

The optical properties of one-dimensional quasiperiodic photonic crystals with linear profiles of modulation parameters are considered. It is shown that such systems possess a wider photonic band gap as compared to the ideal periodic system and can be used as omnidirectional reflectors. The asymmetric profiles of parameters in these systems results in the appearance of nonreciprocity of a new type that makes possible their use as the ideal, purely optical diodes.     

An efficient algorithm for computing the dynamic responses of one-dimensional periodic structures and periodic structures with defects

This paper proposes an efficient algorithm for computing the dynamic responses of one-dimensional periodic structures and periodic structures with defects. It uses the symmetric property of the periodic structure and the energy propagation feature of the dynamic system to analyze the algebraic structure of the matrix exponential corresponding to one-dimensional periodic structures and periodic structures with defects. By using the special algebraic structure of this matrix exponential and the precise integration method, an efficient and accurate algorithm is proposed for computing the matrix exponential corresponding to one-dimensional periodic structures or periodic structures with defects. Hence an efficient method is presented for computing the dynamic responses of one-dimensional periodic structures and periodic structures with defects. It is accurate, efficient and saves memory.     

Optical properties of one-dimensional metal-dielectric photonic band-gap structures with low index dielectrics

We report on the design, fabrication and characterization of one dimensional metal-dielectric photonic band-gap structures (MDPBG) using low index dielectric materials. We describe design techniques that compensate for the shortcomings of the low dielectric material. The structures show high, flat, broad passband transmission within the visible spectrum and excellent out of band rejection in the infrared. We demonstrate one such MDPBG with five periods of Al₂O₃/Ag/Al₂O₃ that shows 53 ± 3% transmission over 150 nm within the visible spectrum and an angular variation smaller than 5% within a field-of view of at least 60°. These MDPBGs are thermally insensitive and show good environmental stability.     

Occurrence of faults/APBs in periodic to quasiperiodic transformations

The strip projection method has been used here to establish the structural relationships between various two dimensional quasiperiodic structures and certain well known periodic structures. These periodic structures, designated as unmodulated approximants, can transform into their quasiperiodic counterparts in a continuous fashion. The early stages of such transformations are characterized by the occurrence of faults or APBs. There is considerable high resolution electron microscopy (HREM) and electron diffraction evidence in favour of this in the case of the β-Mn to octagonal quasicrystal, the σ-phase to dodecagonal quasicrystal and the Al₅Ti₃ to quasiperiodic superlattice structure transformations.     

Impurity modes in one-dimensional photonic crystals-analytic approach

Abstract

We investigate the impurity problem in one-dimensional photonic crystals using the two-band Bloch wave approximation. The impurity level, as the lasing mode, is described in terms of the width and the dielectric function of the impurity, which are in fair agreement with the numerical data by the transfer matrix method. The maximum field intensity and the strongest spatial localization occur when the impurity mode is at midgap, indicating large gain enhancement of the lasing mode. The threshold gain and the optimal conditions for the impurity are evaluated. Effects of surface variations are also analysed to further improve the efficiency of the lasing system.     

Thermooptical switching in a one-dimensional photonic crystal

The temperature dependence of the optical transmission spectrum of a one-dimensional multilayer photonic crystal structure with a central defect layer has been studied. The defect was represented by a nematic liquid crystal (5CB) layer with a homeotropic orientation. It is shows that the defect modes exhibit a 10-nm spectral shift due to a change in the refractive index of the liquid crystal in the course of heating-induced transition to the isotropic phase. A comparison of the experimental data to the results of heating-induced transition to the isotropic phase. A comparison of the experimental data to the results of numerical analysis shows the importance of allowance for the decay of defect modes.     

Tunable photonic bandgap in a one-dimensional superconducting-dielectric superlattice

The transmittance of one-dimensional photonic crystals consisting of superconductor and lossless dielectric has been systematically studied through the transfer-matrix method. Obviously, the shift of the photonic bandgap (PBG) becomes more noticeable by adjusting the thicknesses of the dielectric layers than that of superconductor layers. Furthermore, the number of PBGs can be controlled by varying the thicknesses of dielectric layers. Compared to the thicknesses of the dielectric layers, the width of the PBGs is more sensitive to the thicknesses of the superconductor layers. However, the width of the first PBG promptly varies when the thicknesses of the dielectric layers increase from 0 to 40?nm. If the contribution of the normal conducting electrons of the superconductor is nonnegligible, the temperature of the superconductor has no influence on the width of the PBGs. Moreover, the damp coefficient does not affect the PBGs under low-temperature conditions.     

Terahertz wave propagation in one-dimensional periodic dielectrics

We demonstrate the temporal evolution of terahertz (THz) wave propagation in one-dimensional periodic dielectrics. Distributed Bragg reflectors and a resonant cavity are investigated: The structures involve air gaps interleaved between polymer films. Transmitted and reflected broadband THz waves are measured by means of THz time-domain spectroscopy. The experimental results agree well with transfer matrix calculations.     

一维光子晶体完全光子禁带与结构的关系

阐述了完全光子禁带的概念.用光学特征矩阵方法,通过数值模拟计算,讨论了一维光子晶体出现完全光子禁带与晶体结构和介质材料的折射率的密切关系.具体计算了用同样两种介质材料组成3种不同结构的一维光子晶体,对于TM及TE电磁模式在不同入射角下的透射率谱,从中找出它们的完全光子禁带,发现3种结构的完全光子禁带的波长范围及宽度各不相同.另外,研究结果表明组成光子晶体的两种材料的折射率差别越大,两种电磁模的禁带越宽,越容易产生完全光子禁带.简单讨论了完全光子禁带出现的条件.     

Analysing photonic structures in plants

The outer layers of a range of plant tissues, including flower petals, leaves and fruits, exhibit an intriguing variation of microscopic structures. Some of these structures include ordered periodic multilayers and diffraction gratings that give rise to interesting optical appearances. The colour arising from such structures is generally brighter than pigment-based colour. Here, we describe the main types of photonic structures found in plants and discuss the experimental approaches that can be used to analyse them. These experimental approaches allow identification of the physical mechanisms producing structural colours with a high degree of confidence.     

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.     

Wide-field-of-view GaAs/AlxOy one-dimensional photonic crystal filter

The design, fabrication, and characterization of a one-dimensional photonic crystal optical filter that has a relatively narrow, flat-topped passband within a wide stop band and small angular sensitivity is presented. The filter is based on a one-dimensional photonic crystal structure that has multiple defects, facilitating simultaneous minimization of the angular sensitivity and optimization of the passband's characteristics. We use epitaxially grown and selectively oxidized GaAs/AlxOy multilayers to achieve a high-index-contrast material system and incorporate the experimentally determined optical and material properties into the design of the device. A flat-topped bandpass filter with a bandwidth of 65 nm and a wide field of view of 50 degrees is experimentally characterized and compared with the design predictions.     

Gap modes of one-dimensional photonic crystal surface waves

The finite-difference time-domain method is employed for the analysis of coupling of the surface modes of two truncated one-dimensional photonic crystals separated by a gap. The wave vector, field distributions, and existence conditions of the coupled surface modes are investigated. The wave vector of symmetric gap modes increases with decreasing gap width, while that of antisymmetric modes decreases-exactly opposite of the situation for surface plasmons on metallic half-spaces separated by a dielectric gap. Photonic crystal gap modes could easily and effectively be used as nondissipating gap-mode waveguides.     

Time-domain terahertz study of defect formation in one-dimensional photonic crystals

One-dimensional photonic crystals composed of silicon and air layers with and without twinning defect (i.e., a periodicity break where one half of the photonic structure is a mirror image of the other one) are studied by means of terahertz time-domain transmission and reflection spectroscopy. The structure with defect is decomposed into building blocks: two twins and a defect. A phase-sensitive characterization in transmission and reflection allows us to fully determine the transfer matrices of any block and consequently to predict the properties of composed structures regardless of the microstructure of the constituting blocks. It is shown and experimentally demonstrated that the defect level position is controlled by the reflectance phase of the twins. Possible approach of the reflectance phase determination by use of Kramers-Kronig analysis is also discussed.     

A compact optical wavelength splitter in one-dimensional photonic crystal waveguides

A fundamental T-branch in one-dimensional photonic crystal waveguides based on the omnidirectional reflection is constructed. Numerical simulations of this T-branch indicate that without any structural optimization, four high reflectance peaks and three high transmittance peaks appear alternately within a wide enough frequency band. The T-branch with the unique transmission characteristics can be used as a wavelength splitter. Combining the fundamental T-branch with flexible bends of one-dimensional photonic crystal waveguides, we construct simple and compact wavelength splitters with arbitrary branching angles. Those wavelength splitters are expected to be applied to high density photonic integrated circuits.     

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.     

General conditions of polarization-independent transmissions in one-dimensional magnetic photonic crystals

Abstract

Based on the transfer matrix theory, general conditions of polarization-independent transmissions in one-dimensional photonic crystals are derived. It is shown that the polarization-independent transmissions are obtained in photonic crystals consisting of two alternating layers with the same refraction index and optical thickness as well as the mutually reciprocal wave impedance. By using two different photonic crystals satisfying the above relation to constitute the light quantum-well structures, the structures have polarization-independent transmission properties. When a defective layer with wave impedance of 1 is introduced in the photonic crystals, the defective photonic crystals also have the polarization-independent transmission properties. In addition, polarization-independent low-pass spatial filters are achieved based on these photonic crystal structures.     

Properties of defect modes in geometrically chirped one-dimensional photonic crystals

The variation of the transmission coefficient with defect mode frequency in a geometrically chirped photonic crystal with central defect layer has been investigated theoretically using transfer matrix method and validated experimentally by fabricating and characterizing such photonic crystals. The defect mode frequency is extracted by modeling the defect layer as a Fabry-Perot resonant cavity with mirrors replaced by two geometrically chirped photonic crystals. It is shown that the structural asymmetry of the chirped photonic crystals with respect to the central defect layer affects the width of the photonic band gap and also induces coupling variation between the eigenmodes of the defect layer and those at the band edges of the constituent photonic crystals. This leads to variation in the defect mode transmittance across the photonic band gap and introduces notches at positions where the eigenmodes of the band edges have maximum transmission.     

Optimization of photonic crystal structures

We report on the numerical structural optimization of two-dimensional photonic crystal (PhC) power dividers by using two different classes of optimization algorithms, namely, a modified truncated Newton (TN) gradient search as deterministic local optimization scheme and an evolutionary optimization representing the probabilistic global search strategies. Because of the severe accuracy requirements during optimization, the proper PhC device has been simulated by using the multiple-multipole program that is contained in the MaX-1 software package. With both optimizer classes, we found reliable and promising solutions that provide vanishing power reflection and perfect power balance at any specified frequency within the photonic bandgap. This outcome is astonishing in light of the discrete nature inherent in the underlying PhC structure, especially when the optimizer is allowed to intervene only within a very small volume of the device. Even under such limiting constraints structural optimization is not only feasible but has proven to be highly successful.     

Nanodiamond particles forming photonic structures

Colloid suspensions of irregularly shaped, highly charged detonation nanodiamond particles are found to have unexpected optical properties, similar to those of photonic crystals. This finding is all the more surprising since the particles used in this work are far more polydisperse than those typically forming photonic crystals. Intensely iridescent structures have been fabricated using the centrifugation of aqueous suspensions of nanodiamonds.