Photonic Quasicrystals Research Articles

Improvement efficiency of thin-film solar cell by plasmonic properties of silver

Thin-film silicon solar cells need light trapping mechanisms to enhance the efficiency due to silicon’s weak absorption of light. In this paper, by use of rigorous coupled-wave analysis (RCWA), we propose and simulate a light-trapping quasi-photonic crystal plasmonic thin-film silicon solar cell consisting of an anti-reflection coating (ARC) with refractive index nAR=1.9 and thickness (TAR=0.06μm), a silicon active layer with thickness Tc=0.45μm, a grating surfaces composed of silver and a one-dimensional quasi-photonic crystal composed of SiO2/Si layers. Results show that for proposed structure the cell efficiency arrive to 14.3% for TM with p=0.181μm and 11.71% for TE mode with p=0.42μm which has a significant increase compare usual and similar thin-film silicon solar cells.

Generation of terahertz hollow beams by a photonic quasi-crystal flat lens

We have designed a decagonal photonic quasi-crystal (PQC) flat lens, which turns an incident terahertz (THz) plane wave into a hollow beam easily and flexibly. The features of the THz hollow beam can be controlled by varying the parameters of a point defect in the center of the lens, i.e., the PQC flat lens can be used as a flexible tool for THz optical captivity or optical tweezer. The results showing that an airy disk, whose mean beam width is similar to the incident wavelength and power-in-the-bucket (PIB) is more than 96%, can be generated in the far field.

Planar scanning method for detecting refraction characteristics of two-dimensional photonic quasi-crystal wedge-shaped prisms.

In this study, a planar scanning method is proposed. This novel method adapts two monitors moving along double planar tracks that can be used to detect refraction characteristics of two-dimensional (2D) photonic quasi-crystal (PQC) wedge-shaped prisms. Refraction of a decagonal Penrose-type PQC prism is analyzed for a given incident beam and two polarization modes at different incident positions in the prism using this method. Refraction from the prism is irregular, indicating that nonuniformity in the arrangement of scatterers in the prism causes Bragg-like scattering irregularities. Numerical results show that this method can be used for guiding the design of a 2D PQC prism and for the analysis of its refraction characteristics.

Fabrication of photonic quasicrystalline structures in the sub-micrometer scale

Compared to periodic crystals, photonic quasicrystals (PQC) have higher point group symmetry and are more favorable in achieving complete band-gaps. In this report, a top-cut prism interferometer is designed to fabricate ten-fold photonic quasicrystalline structures in the sub-micro scale. Based on the difference of production conditions, a variety of quasicrystals have been obtained in the SU8 photoresist films. Scanning Probe Microscopy and laser diffraction are used to characterize the produced structures. The corresponding theoretical analysis is also provided to compare with the experimental results. This will provide guidance for the large-area and fast production of ten-fold quasicrystalline structures with high quality.

A simple configuration for fabrication of 2D and 3D photonic quasicrystals with complex structures

A simple method using a single-prism common-path interferometer is presented for the fabrication of complex quasicrystals in sub-micrometer scales. Multiple types of two-dimensional (2D) and three-dimensional (3D) quasicrystalline structures are designed and their diffraction patterns are obtained by using Fourier Transform method. Multi-fold rotational symmetries are demonstrated and compared. By using this method, a wide range of quasicrystals types can be produced with arbitrary complexities and rotational symmetries. The transmittance studies of 12-fold and 18-fold structures also reveal the existence of complete photonic bandgaps, which also demonstrates increased symmetry and significantly improved characteristics of photonic band-gaps.

Energy landscape in a Penrose tiling

Since their spectacular experimental realisation in the early 80's, quasicrystals have been the subject of very active research, whose domains extend far beyond the scope of solid state physics. In optics, for instance, photonic quasicrystals have attracted strong interest for their specific behaviour, induced by the particular spectral properties, in light transport, plasmonic and laser action. Very recently, one of the most salient spectral feature of quasicrystals, namely the gap labelling, has been observed for a polariton gas confined in a one dimensional quasi-periodic cavity. This experimental result confirms a theory which is now very complete in dimension one. In dimension greater than one, the theory is very far from being complete. Furthermore, some intriguing phenomena, like the existence of self-similar eigenmodes can occur. All this makes two dimensional experimental realisations and numerical simulations pertinent and attractive. Here, we report on measurements and energy-scaling analysis of the gap labelling and the spatial intensity distribution of the eigenstates for a microwave Penrose-tiled quasicrystal. Far from being restricted to the microwave system under consideration, our results apply to a more general class of systems.

Topological Photonic Quasicrystals: Fractal Topological Spectrum and Protected Transport

We show that it is possible to have a topological phase in two-dimensional quasicrystals without any magnetic field applied, but instead introducing an artificial gauge field via dynamic modulation. This topological quasicrystal exhibits scatter-free unidirectional edge states that are extended along the system's perimeter, contrary to the states of an ordinary quasicrystal system, which are characterized by power-law decay. We find that the spectrum of this Floquet topological quasicrystal exhibits a rich fractal (self-similar) structure of topological "minigaps," manifesting an entirely new phenomenon: fractal topological systems. These topological minigaps form only when the system size is sufficiently large because their gapless edge states penetrate deep into the bulk. Hence, the topological structure emerges as a function of the system size, contrary to periodic systems where the topological phase can be completely characterized by the unit cell. We demonstrate the existence of this topological phase both by using a topological index (Bott index) and by studying the unidirectional transport of the gapless edge states and its robustness in the presence of defects. Our specific model is a Penrose lattice of helical optical waveguides - a photonic Floquet quasicrystal; however, we expect this new topological quasicrystal phase to be universal.

Narrow stop band optical filter using one-dimensional regular Fibonacci/Rudin Shapiro photonic quasicrystals

One-dimensional deterministic aperiodic multilayered photonic crystals can be formed by stacking together dielectric layers of several different types according to substitutional generalized Fibonacci or Rudin Shapiro sequences. An efficient numerical technique based on calculus of transfer matrix of multiple layers is used to study the formation of optical gaps. The quasi-periodicic distribution gives some interesting optical properties and offers a multitude of adjacent pseudo-band gaps in different frequency range. The potential of photonic structure are explored by varying the structural parameters. The presence of band gaps due to long-range correlations. Further analysis shows that the central frequency of transmission band (stop band) can be changed by varying the type of distribution of two considered layers which formed the all quasi-photonic crystals cells and the order of quasiperiodic sequences. The structure is exploited to design selective optical filters with narrow band gaps and polychromatic stop band filters. These results make aperiodic photonic structures very attractive for the engineering of novel passive photonic.

Chromatic Dispersion of an Optical Fiber Based on Photonic Quasicrystals with Twelve-Fold Symmetry and its Application as Directional Coupling

Optical fibers composed by photonic quasicrystals it is based on aperiodic structures characterized by at least two different symmetrical patterns from the base matrix. In this work, an optical fiber composed by quasi-periodic and symmetric matrix was analyzed using the finite element method in conjunction with cylindrical perfectly matched layers. The structure is composed by pure silica and/or silica doped with germanium, and originated from twelve distributions of air holes symmetrically with a defect caused by the absence of the fiber central hole. The obtained results shown that the structure in analysis exhibits an ultra-flat chromatic dispersion for a range of wavelengths varying from 1.4 to 1.6 µm covering the bands E,S, C and L, with chromatic dispersion, for the silica doped with germanium, varying between 22.1 and 23.01 [ps.km-1.nm-1]. This photonic quasicrystal fiber (PQCF) was used to form a coupler with three identical horizontal cores surrounded by air holes. The signal power launched in the central core is equally divided between the two neighboring cores with 50% of the coupling ratio.

Expressions for reflection and transmission coefficients for one-dimensional photonic quasicrystals

We give general expressions for the light reflection and transmission coefficients for one-dimensional (1D) photonic quasicrystals in the framework of the so-called two-wave approximation. A special attention is paid to quasicrystals composed of dielectric layers, where the reflection and transmission coefficients as a function of the length of the structure take a simple form. The expression for the diffraction vectors of a 1D quasicrystal with an arbitrary number of different constituent segments is discussed as well.

Anomalous optical Anderson localization in mixed one dimensional photonic quasicrystals.

Anomalous optical Anderson localization (AOAL) in mixed one-dimensional (1D) photonic quasicrystals with matching impedance is obtained when the average refractive index of left- and right-handed layers is approximately zero. The transport properties of ordinary and anomalous localization are investigated and compared. The difficulties in expressing analytically the scaling factors of the mixed photonic quasicrystals are illustrated from Hamiltonian-map analysis. An approach based on transfer matrix method is proposed to simulate the localization behavior. From the simulation, it is found that the narrow distribution of the phase shift is responsible for AOAL in the mixed photonic structures. The scaling factors of AOAL decrease with the broadening of the phase shift distribution. The maximum phase shifts of the mixed photonic structures determine the lower boundary of the anomalous localization.

Making invisible materials

All-dielectric photonic quasicrystals may act as zero-refractive-index homogeneous materials despite their lack of translational symmetry and periodicity, stretching wavelengths to infinity and offering applications in light wavefront sculpting and optical cloaking.

Thermal Emission Control via Bandgap Engineering in Aperiodically Designed Nanophotonic Devices.

Aperiodic photonic crystals can open up novel routes for more efficient photon management due to increased degrees of freedom in their design along with the unique properties brought about by the long-range aperiodic order as compared to their periodic counterparts. In this work we first describe the fundamental notions underlying the idea of thermal emission/absorption control on the basis of the systematic use of aperiodic multilayer designs in photonic quasicrystals. Then, we illustrate the potential applications of this approach in order to enhance the performance of daytime radiative coolers and solar thermoelectric energy generators.

Octonacci photonic quasicrystals

We study theoretically the transmission spectra in one-dimensional photonic quasicrystals, made up of SiO2(A) and TiO2(B) materials, organized following the Octonacci sequence, where the nth-stage of the multilayer Sn is given by the rule Sn=Sn-1Sn-2Sn-1, for n⩾3 and with S1=A and S2=B. The expression for transmittance was obtained by employing a theoretical calculation based on the transfer-matrix method. For normally incident waves, we observe that, for a same generation, the transmission spectra for transverse electric (TE) and transverse magnetic (TM) waves are equal, at least qualitatively, and they present a scaling property where a self-similar behavior is obtained, as an evidence that these spectra are fractals. The spectra show regions where the omnidirectional band gaps emerges for specific generations of Octonacci photonic structure, except to TM waves. For TE waves, we note that all of them have almost the same width, for different generations. We also report the localization of modes as a consequence of the quasiperiodicity of the heterostructure.

Conical Dispersion and Effective Zero Refractive Index in Photonic Quasicrystals

It is recognized that for a certain class of periodic photonic crystals, conical dispersion can be related to a zero-refractive index. It is not obvious whether such a notion can be extended to a noncrystalline system. We show that certain photonic quasicrystalline approximants have conical dispersions at the zone center with a triply degenerate state at the Dirac frequency, which is the necessary condition to qualify as a zero-refractive-index medium. The states in the conical dispersions are extended and have a nearly constant phase. Experimental characterizations of finite-sized samples show evidence that the photonic quasicrystals do behave as a near zero-refractive-index material around the Dirac frequency.

Five-fold Symmetric Photonic Quasi-crystal Fiber with High Negative Dispersion

Dispersion causes optical pulses broadening and must be compensated for in long-distance high-speed optical data transmission systems. We investigate optical properties of micro structured fiber with 5-fold symmetric quasicrystal lattice of air-holes in a silica matrix for the first time. Dual-Concentric core Photonic Quasicrystal Fiber (DC-PQF) lattices with varying hole diameters were investigated and curves for the effective index, dispersion parameter and confinement losses were calculated by finite element method. For dispersion compensation purpose, we have proposed a novel 5-fold PQF with a high negative dispersion values ≈ 16,000 ps/(nm-km) could be reached for the wavelength around 1310 nm.

Photonic quasicrystal nanopatterned silicon thin film for photovoltaic applications

In this paper, the authors numerically studied the optical properties of a silicon photonic quasicrystal (PQC) nanohole array for photovoltaic applications. With the same active layer thickness, the ultimate efficiency of a solar cell integrated with an optimized PQC nanohole array can be enhanced by 9.01% and 1.40% compared to that with an ordered square lattice of a nanohole array and a random nanohole array, respectively. The absorptance enhancement is mainly due to the higher-order rotational symmetry in PQC structures, which leads to the presence of additional resonant modes, the broadening of existing modes and the reduction of surface reflectance. The angular response for both transverse-electric and transverse-magnetic modes are also analyzed in detail.

Experimental and theoretical investigation of macro-periodic and micro-random nanostructures with simultaneously spatial translational symmetry and long-range order breaking.

Photonic and plasmonic quasicrystals, comprising well-designed and regularly-arranged patterns but lacking spatial translational symmetry, show sharp diffraction patterns resulting from their long-range order in spatial domain. Here we demonstrate that plasmonic structure, which is macroscopically arranged with spatial periodicity and microscopically constructed by random metal nanostructures, can also exhibit the diffraction effect experimentally, despite both of the translational symmetry and long-range order are broken in spatial domain simultaneously. With strategically pre-formed metal nano-seeds, the tunable macroscopically periodic (macro-periodic) pattern composed from microscopically random (micro-random) nanoplate-based silver structures are fabricated chemically through photon driven growth using simple light source with low photon energy and low optical power density. The geometry of the micro-structure can be further modified through simple thermal annealing. While the random metal nanostructures suppress high-order Floquet spectra of the spatial distribution of refractive indices, the maintained low-order Floquet spectra after the ensemble averaging are responsible for the observed diffraction effect. A theoretical approach has also been established to describe and understand the macro-periodic and micro-random structures with different micro-geometries. The easy fabrication and comprehensive understanding of this metal structure will be beneficial for its application in plasmonics, photonics and optoelectronics.

Nanostructured PEDOT:PSS film with two-dimensional photonic quasi crystals for efficient white OLED devices

Polymeric nanostructured highly conductive films with Photonic Quasi Crystal topologies are presented with possibilities to open the path towards highly efficient white OLEDs.

单棱镜共光路干涉法制作多结构二维光子准晶

单棱镜共光路干涉法制作多结构二维光子准晶