Layered Photonic Crystals Research Articles

One-Dimensional Defect Layer Photonic Crystal Sensor for Purity Assessment of Organic Solvents.

This paper presents the design and analysis of a one-dimensional defect layer photonic crystal (1D-DLPC) sensor for the assessment of the purity of chemical solvents with enhanced accuracy. Chemical solvents are frequently used in chemical processes as reaction mediums. It is essential to ascertain its purity since impurities can significantly affect the outcome of the reaction. The structure of the proposed one-dimensional defect layer photonic crystal sensor consists of a defect layer sandwiched between alternate layers of ZnO and SiO2 organized with a certain periodicity. It has been shown that the localized defect modes inside the structure can detect minute refractive index changes based on the degree of impurity of chemical solvents. Simulation studies have been performed through the transfer matrix method (TMM) and the performance of the design is evaluated using several metrics such as sensitivity, full width at half-maximum, figure of merit, quality factor, and dynamic range. Results indicate that the designed one-dimensional defect layer photonic crystal sensor has a significantly high efficiency and is suitable for detecting impure solvents.

Tunable interface state in one dimensional composite photonic structure

Based on the Transfer Matrix method (TMM), we evaluate the conditions and controllability of interface states in one-dimensional photonic structures composed of two binary layered photonic crystals, PCI and PCII, having the same photonic bandgaps but different unit cells. For PCs with inversion symmetry but different symmetry centers, the composite photonic structure exhibits interface states in the middle of the corresponding bandgaps where the sum of the reflection phases of the PCs is zero. The observed interface states persist even when the inversion symmetry is broken by shifting the unit cell of the individual PC as long as the sum of the reflection phases is still zero. Moreover, the location of interface states inside the bandgaps can be controlled by adjusting the thicknesses of the adjacent layers at the interface of two PCs. The composite photonic structure can be realized easily by standard electron beam evaporation technology, opening more possible applications in multi-channel narrowband filters and other optical modulation devices.

Asymmetric band diagrams in photonic crystals with a spontaneous nonreciprocal response

We study the propagation of electromagnetic waves in layered photonic crystals formed by materials with a spontaneous nonreciprocal response, such as Tellegen (axion) media or topological insulators. Surprisingly, it is proven that stratified Tellegen photonic crystals that break simultaneously the space inversion and time-reversal symmetries have always symmetric dispersion diagrams. Interestingly, we show that by combining chiral and nonreciprocal materials the photonic band diagrams can exhibit a spectral asymmetry such that $\ensuremath{\omega}(\mathbf{k})\ensuremath{\ne}\ensuremath{\omega}(\ensuremath{-}\mathbf{k})$. Furthermore, it is demonstrated that in some conditions two juxtaposed Tellegen medium layers have an electromagnetic response analogous to that of a biased ferrite slab.

Double-layer Fano resonance photonic crystal filters

We report ultra-compact surface-normal high-Q optical filters based on single- and double-layer stacked Fano resonance photonic crystal slabs on both Si and quartz substrates. A single layer photonic crystal filter was designed and a Q factor of 1,737 was obtained with 23 dB extinction ratio. With stacked double-layer photonic crystal configuration, the optical filter Q can increase to over 10,000,000 in design. Double-layer filters with quality factor of 9,734 and extinction ratio of 8 dB were experimentally demonstrated, for a filter design with target Q of 22,000.

Mesoscopic Self-Collimation and Slow Light in All-Positive Index Layered Photonic Crystals

We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows us to combine slow-light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air.

The Langmuir‐Blodgett Approach to Making Colloidal Photonic Crystals from Silica Spheres

The area of colloidal photonic crystal research has attracted enormous attention in recent years as a result of the potential of such materials to provide the means of fabricating new or improved photonic devices. As an area where chemistry still predominates over engineering the field is still in its infancy in terms of finding real applications being limited by ease of fabrication, reproducibility and 'quality'- for example the extent to which ordered structures may be prepared over large areas. It is our contention that the Langmuir-Blodgett assembly method when applied to colloidal particles of silica and perhaps other materials, offers a way of overcoming these issues. To this end the assembly of silica and other particles into colloidal photonic crystals using the Langmuir-Blodgett (LB) method is described and some of the numerous papers on this topic, which have been published, are reviewed. It is shown that the layer-by-layer control of photonic crystal growth afforded by the LB method allows for the fabrication of a range of novel, layered photonic crystals that may not be easily assembled using any other approach. Some of the more interesting of these structures, including so-called heterostructured photonic crystals comprising of layers of spheres having different diameters are presented and their optical properties described. Finally, we offer our comments as to future applications of this interesting technology.

Optimal light trapping in ultra-thin photonic crystal crystalline silicon solar cells

Crystalline silicon is an attractive photovoltaic material because of its natural abundance, accumulated materials and process knowledge, and its appropriate band gap. To reduce cost, thin films of crystalline silicon can be used. This reduces the amount of material needed and allows material with shorter carrier diffusion lengths to be used. However, the indirect band gap of silicon requires that a light trapping approach be used to maximize optical absorption. Here, a photonic crystal (PC) based approach is used to maximize solar light harvesting in a 400 nm-thick silicon layer by tuning the coupling strength of incident radiation to quasiguided modes over a broad spectral range. The structure consists of a double layer PC with the upper layer having holes which have a smaller radius compared to the holes in the lower layer. We show that the spectrally averaged fraction of photons absorbed is increased 8-fold compared to a planar cell with equivalent volume of active material. This results in an enhancement of maximum achievable photocurrent density from 7.1 mA/cm(2) for an unstructured film to 21.8 mA/cm(2) for a film structured as the double layer photonic crystal. This photocurrent density value approaches the limit of 26.5 mA/cm(2), obtained using the Yablonovitch light trapping limit for the same volume of active material.

Light propagation in layered photonic crystals with admixture layers

Abstract The virtual-crystal approximation is used for numerical simulation of a polariton spectrum transformation in composite materials, consisting of alternating silicon and liquid crystal layers and randomly included admixture layers. The character of dependence of the bandgap width and the refractive index upon the concentra-tion of admixture layers is discussed. It is shown that the energy structure of this imperfect superlattice can be significantly altered by implantation of appropriate defect layers. Keywords: photonic crystal, Si - liquid crystal system, admixture layer, bandgap width. PACS: 78.66.-w UDC: 535.3 1. Introduction Propagation of electromagnetic waves in thin films and layered crystalline media is cur-rently drawing a close attention of researchers. The works [1–4] give the account of the related researches carried out for photonic crystals and [5] – for some composite materials based on silicon and liquid crystals. On the one hand, the interest towards these objects is due to their significance for electronics. On the other hand, this is because a notable ad-vance of technology that allows growing of ultra-thin films and periodic structures with controlled characteristics. There have been numerous theoretical and experimental studies (see, e.g., [6] and references therein) on exciton-like excitations in ideal dielectric superlattices. A general theory of optical waves in anisotropic crystals, including those formed of macroscopic layers, has been discussed in Ref. [7]. The authors [8] have investigated dispersion of po-laritons in a superlattice with two admixture layers. At the same time, a considerable in-terest has been focused on non-ideal superlattices with an arbitrary number of admixture layers, as well as on dependence of polariton spectrum on the concentration of corre-sponding defects. Further development of the theory of layered structures evidently re-quires considering more complex models like superlattices with randomly included ad-mixture layers of variable composition. A better understanding of how the optical proper-

Statistical theory of multiple scattering of waves applied to three-dimensional layered photonic crystals

On the basis of the statistical theory of multiple scattering of waves, we offer a numerical approach to calculate coherent transmission and reflection for the three-dimensional (3-D) photonic crystals that consist of partially disordered dielectric spheres. With the proposed scheme, which we call the transfer-matrix (TM) method with quasi-crystalline approximation (QCA), we consider a quasi-regular 3-D assembly of particles as a stack of close-packed monolayers with a short-range ordering. Single-scattering characteristics are determined by Mie theory. Lateral electrodynamic coupling between the particles of a monolayer is treated in the QCA. Multibeam interference between monolayers is described in a manner analogous to the TM technique. We apply the TM-QCA calculation technique to study two revealed effects: (1) short-wavelength attenuation due to particles of finite sizes and (2) nonmonotonic dependence of the pseudogap depth on the particle size, refractive-index contrast, and intermonolayer distances.

Optical properties of monolayer lattice and three-dimensional photonic crystals using dielectric spheres

The transmittance spectra for the monolayer triangle lattice using millimeter-sized ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ spheres are measured and calculated at various incident angles of electromagnetic waves. From the results, the dispersion of photonic bands for the monolayer triangle lattice is obtained. Furthermore, the transmittance spectra of three-dimensional layered photonic crystals are measured for different layer numbers and different air gaps. Theoretical analysis shows that the photonic band gaps refer to the anticrossing between heavy photon bands and light photon bands. Finally, we discuss the future prospect of the photonic crystals using dielectric spheres.