Full Photonic Band Gap Research Articles

Phoxonic bandgap modulation in optomechanical crystals with shifting hole

Optomechanical crystals (OMCs) control light and mechanical vibrations by simultaneously presenting photonic and phononic bandgaps. Tuning the position of these bandgaps is essential to address different technological applications. In this study, we present a one-dimensional OMC with wings and a hole whose position is shifting sideways. Simulations of the photonic and phononic band diagrams show that the hole shift effectively controls the width and position of the band gaps. Furthermore, the hole shift also opens new photonic bandgaps that extend the frequency range with full photonic bandgaps. The width of the phononic bandgap is maximum for a hole shift to be 42% wider than without a hole shift. Despite large band movements induced by the hole shift, the average displacement is null, which means that the hole shift does not impact the photon and phonon density of states (DOS). These results can be used to optimize the design of optomechanical cavities for specific frequency range applications.

Design of phoxonic filter using locally-resonant cavities

A phoxonic crystal structure with a full phononic and photonic band gap is designed in this study, which is capable of conducting sound waves and also light waves with transverse magnetic (TM) polarization. Materials used in the structures are nylon and molybdenum, both of which have adequate difference in refractive index and elastic constants. It is worth of noting that the filling factor is considered to be 28% in all of the structures, in order to ease of fabrication. The final phoxonic filter structure is obtained by the comparison of several phoxonic filter structures in a similar condition. Since it is difficult to coordinate light and sound in phoxonic structures, the proposed structure has some advantages compared to other filters. This structure shows the optical and acoustical transmission linewidths equal 3.8 KHz in phononic and 0.06 nm in photonic modes, respectively. Also, the output quality factor is 23699 in phononic and 21201 in photonic modes. Finite element, plane wave expansion, and finite-difference time-domain methods are utilized for simulation.

Additive Manufacturing of High-Refractive-Index, Nanoarchitected Titanium Dioxide for 3D Dielectric Photonic Crystals.

Additive manufacturing at small scales enables advances in micro- and nanoelectromechanical systems, micro-optics, and medical devices. Materials that lend themselves to AM at the nanoscale, especially for optical applications, are limited. State-of-the-art AM processes for high-refractive-index materials typically suffer from high porosity and poor repeatability and require complex experimental procedures. We developed an AM process to fabricate complex 3D architectures out of fully dense titanium dioxide (TiO2) with a refractive index of 2.3 and nanosized critical dimensions. Transmission electron microscopy (TEM) analysis proves this material to be rutile phase of nanocrystalline TiO2, with an average grain size of 110 nm and <1% porosity. Proof-of-concept woodpile architectures with 300-600 nm beam dimensions exhibit a full photonic band gap centered at 1.8-2.9 μm, asrevealed by Fourier-transform infrared spectroscopy (FTIR) and supported by plane wave expansion simulations. The developed AM process enables advances in 3D MEMS, micro-optics, and prototyping of 3D dielectric PhCs.

Tuning full photonic band gap with plasma frequency in two-dimensional photonic crystals composed of anisotropic dielectric rods in plasma background

In this study, we analyze full photonic band gap formation and properties of two-dimensional photonic crystals with square lattice, composed of anisotropic tellurium rods with different geometric shapes in a plasma background. Using the finite-difference time-domain method, we discuss the tunability of the full photonic band gap width as a function of the plasma frequency for different values of tellurium rod’s parameters. The calculated results show that our proposed structures represent full photonic band gaps with considerable width, which are dependent on plasma frequency.

Self-assembled three-dimensional inverted photonic crystals on a photonic chip

Three dimensional photonic crystals (PhCs) exhibiting a full photonic band gap have high potential in optical signal processing and detector applications. However, the challenges in the integration of the 3D PhCs into photonic circuits have so far hindered their exploitation in real devices. This article demonstrates the fabrication of 3D PhCs exploiting the capillary directed self-assembly (CDSA) of monodisperse colloidal silica spheres, their inversion to silicon shells, and integration with silicon waveguides. The measured transmission characteristics agree with numerical predictions and provide strong indication of a full photonic band gap in the inverted 3D photonic crystals at wavelengths close to 1.55 μm. Silicon inverted photonic crystal self-assembled into a cavity in a waveguide intersection and the corresponding photonic band structure of the crystal, together with the simulated transmission, reflection, and absorption spectra.

Optomechanical coupling in the Anderson-localization regime

Optomechanical crystals, purposely designed and fabricated semiconductor nanostructures, are used to enhance the coupling between the electromagnetic field and the mechanical vibrations of matter at the nanoscale. However, in real optomechanical crystals, imperfections open extra channels where the transfer of energy is lost, reducing the optomechanical coupling eficiency. Here, we quantify the role of disorder in a paradigmatic one-dimensional optomechanical crystal with full phononic and photonic bandgaps. We show how disorder can be exploited as a resource to enhance the optomechanical coupling beyond engineered structures, thus providing a new toolset for optomechanics.

Full photonic band gap properties of plasma photonic crystals with triangular structure

In this study, we analyse full photonic band gap (PBG) properties of two-dimensional plasma photonic crystals (PCs) with triangular lattice, composed of anisotropic tellurium rods with different geometrical shapes immersed in plasma background. Using the finite-difference time-domain method, we discuss the maximization of the full PBG width as a function of tellurium rods parameters with different shapes and orientations. The numerical results show that our proposed structures represent significant large full PBGs in comparison to previously studied plasma PCs.

Amplifying and compressing optical filter based on one-dimensional ternary photonic crystal structure containing gain medium

The transmission spectrum properties of the one-dimensional ternary photonic crystal (1DTPC) structure, composed of dielectric (D), metal (M) and gain (G) materials, with three different arrangements of (DGM)N, (GDM)N and (DMG)N, where N is the number of periodicity, were investigated. Two full photonic band gaps and N−1 resonant peaks, localized between them, were observed on transmittance spectra on near-UV spectrum region. When the gained layer was placed in front of the metal, the peaks appeared with higher resolution. There is a peak, localized on the higher band-edge of the first gap, which shows very interesting property than the other peaks. Thus, it amplifies and compresses faster with increase in the N and strength of the gain coefficient. The effects of the gain coefficient and periodicity number are graphically illustrated. This communication presents a PC structure that can be a good candidate to design an amplifying and compressing single or multi-channel optical filter in the UV region.

2D photonic crystal complete band gap search using a cyclic cellular automaton refination

We present a refination method based on a cyclic cellular automaton (CCA) that simulates a crystallization-like process, aided with a heuristic evolutionary method called differential evolution (DE) used to perform an ordered search of full photonic band gaps (FPBGs) in a 2D photonic crystal (PC). The solution is proposed as a combinatorial optimization of the elements in a binary array. These elements represent the existence or absence of a dielectric material surrounded by air, thus representing a general geometry whose search space is defined by the number of elements in such array. A block-iterative frequency-domain method was used to compute the FPBGs on a PC, when present. DE has proved to be useful in combinatorial problems and we also present an implementation feature that takes advantage of the periodic nature of PCs to enhance the convergence of this algorithm. Finally, we used this methodology to find a PC structure with a 19% bandgap-to-midgap ratio without requiring previous information of suboptimal configurations and we made a statistical study of how it is affected by disorder in the borders of the structure compared with a previous work that uses a genetic algorithm.

Investigation of the effect of noncircular scatterers on the band structure of anisotropic photonic crystal slabs

Using the supercell approach based on the plane wave expansion method, we analyze the photonic bandgap (PBG) of square and triangular photonic crystal slabs composed of air holes in an anisotropic tellurium background with SiO(2) as cladding material. Two shapes (square and hexagonal) are considered for air holes. We discuss the maximization of the full PBG width as a function of noncircular air hole parameters, their orientation, and also slab thickness. The numerical results show that both structures represent a full PBG with noticeable width, which can be helpful for designing optical devices.

3D titania photonic crystals replicated from gyroid structures in butterfly wing scales: approaching full band gaps at visible wavelengths

3D titania photonic crystals are replicated from single gyroid structures found in the butterfly Callophrys rubi. Photonic crystals were characterised using SEM imaging, X-ray and Raman scattering and reflection spectroscopy. The overall symmetry and topology of the original single gyroid structures is replicated with high fidelity. Titania replicas display photonic responses that are thermal history dependent. Replicas treated at 700 °C, show up to 96% reflectivity at ∼505 nm, while at lower and higher treatment temperatures the photonic response was not as pronounced. Simulated band structures fitted to the observed spectral reflectivity data constrain the solid volume fractions and dielectric constants of the replicas. The titania photonic crystals were also found to be optically active, with both left- and right-handed single gyroids contributing to the chiral response. The 3D titania photonic crystals replicated here have nearly complete overlapping of partial band gaps, strongly suggesting that materials with full photonic band gaps are experimentally within reach using the general replication approach reported here.

Theoretical Analysis of Band Gap of 2-D Square Photonic Crystals Fabricated by Dual-Step Dual-Team Holographic Method

The dual-step dual-team holographic method to fabricate square lattices is proposed. The effect of intensity threshold was analyzed by calculating the intensity spatial distribution. The photonic band gap properties of two-dimensional square lattice fabricated by holographic lithography are investigated numerically. The influences of intensity threshold and dielectric contrast on photonic gap are comprehensively studied by plane wave expansion method. Calculations of band structure as a function of the intensity threshold show that the full photonic band gap does not increase monotonically with dielectric contrast ratio, but has a peak value instead by studying the relation between the complete PBG and the dielectric contrast.

Sculpturing of photonic crystals by ion beam lithography: towards complete photonic bandgap at visible wavelengths

Three dimensional (3D) ion beam lithography (IBL) is used to directly pattern 3D photonic crystal (PhC) structures in crystalline titania. The process is maskless and direct write. The slanted pore 3D structures with pore diameters of 100 nm having aspect ratio of 8 were formed. It is shown that chemical enhancement of titania removal up to 5.2 times is possible in XeF2 gas for the closest nozzle-to-sample distance; the enhancement was ∼ 1.5 times for the actual 3D patterning due to a sample tilt. Tolerances of structural parameters and optimization of IBL processing required for the fabrication of PhCs with full photonic bandgap in visible spectral range in rutile are outlined. Application potential of 3D-IBL is discussed.

Tunneling of ultradirective radiation in metamaterials with zero-average index bandgap

In a zero-average refractive index metamaterial the light propagation is forbidden and a narrow full photonic bandgap is open in correspondence of the frequency where it vanishes and the refractive index is averaged over the volume. However, it should be underlined that Fabry-Presonances can open a propagation state inside such a particular type of bandgap. Based on a photonic crystal exhibiting a negative refractive index, it was found that such Fabry- Presonant states allow images transmission with subwavelength details. C 2011 Society of

Decay of a quantum dot in two-dimensional metallic photonic crystals

In this paper we have developed a theory for the decay of a quantum dot doped in a two-dimensional metallic photonic crystal consisting of two different metallic pillars in an air background medium. This crystal structure forms a full two-dimensional photonic band gap when the appropriate pillar sizes are chosen. The advantage of using two metals is that one can easily control the density of states and optical properties of these photonic crystals by changing the plasma energies of two metals rather than one. Using the Schrödinger equation method and the photonic density of states, we calculated the linewidth broadening and the spectral function of radiation due to spontaneous emission for two-level quantum dots doped in the system. Our results show that by changing the plasma energies one can control spontaneous emission of quantum dots doped in the metallic photonic crystal.

Dimer‐Based Three‐Dimensional Photonic Crystals

AbstractThe self‐assembly of polystyrene dimer‐ and spherocylinder‐shaped colloids is achieved via controlled drying on glass and silicon substrates. 3D monoclinic colloidal crystal structures are determined from scanning electron microscopy images of sections prepared using focused ion‐beam (FIB) milling. Full photonic bandgaps between the eighth and ninth bands are found for a systematic range of colloidal dimer shapes explored with respect to the degree of constituent lobe fusion and radius ratio. The pseudogap between bands 2 and 3 for spherocylinder‐based monoclinic crystals is also probed using normal incidence reflection spectroscopy.

Deep and tapered silicon photonic crystals for achieving anti-reflection and enhanced absorption

Tapered silicon photonic crystals (PhCs) with smooth sidewalls are realized using a novel single-step deep reactive ion etching. The PhCs can significantly reduce the surface reflection over the wavelength range between the ultra-violet and near-infrared regions. From the measurements using a spectrophotometer and an angle-variable spectroscopic ellipsometer, the sub-wavelength periodic structure can provide a broad and angular-independent antireflective window in the visible region for the TE-polarized light. The PhCs with tapered rods can further reduce the reflection due to a gradually changed effective index. On the other hand, strong optical resonances for TM-mode can be found in this structure, which is mainly due to the existence of full photonic bandgaps inside the material. Such resonance can enhance the optical absorption inside the silicon PhCs due to its increased optical paths. With the help of both antireflective and absorption-enhanced characteristics in this structure, the PhCs can be used for various applications.

Full-photonic-bandgap structures for prospective dye-sensitized solar cells

The photonic bands of various TiO 2 photonic crystals filled with acetonitrile were investigated with the perspective for application to dye-sensitized solar cells. Finite-difference time-domain methods revealed that three-dimensional (3D) photonic crystals with diamond-log and inverse-diamond-log structures composed of TiO 2 and an electrolyte had full photonic band gaps under certain conditions. The quality factor of the band gap and the electrolyte filling factor of the structures were optimized. Moreover, with the consideration for easy fabrication of such photonic crystals, two-dimensional (2D) photonic crystals, i.e., TiO 2 slabs with square holes filled with electrolytes, were also investigated. Two-dimensional structures that have a full photonic band gap were also discovered. These discoveries may lead to early electrochemical applications of dye-sensitized photonic-crystal electrodes.

Fabrication of three-dimensional terahertz photonic crystals with diamond structure by particle manipulation assembly

We reported the fabrication of terahertz photonic crystals by three-dimensional (3D) particle manipulation assembly. Our method, which is based on pick-and-place manipulation and interparticle laser welding, enabled accurate assembling of an arbitrary 3D structure, regardless of particle polydispersity. By using this method, we fabricated a diamond crystal from ZrO2/polyethylene composite particles (diameter of 400 μm). The obtained crystal exhibited a photonic stop gap in the ⟨111⟩ direction; this result was in good agreement with the theoretical result, suggesting that the crystal has a full photonic bandgap at around 0.2 THz.

A Chemical Synthetic Route towards “Colloidal Molecules”

A non-exhaustive list of fields in which extensive research has been dedicated to colloidal particles during the past century includes condensed matter physics, biology, optics, materials science, and chemistry. Both our current understanding of various physical phenomena and our capability to fabricate new functional materials have been considerably enriched by the development of synthetic strategies that are capable of generating copious quantities of colloidal entities of good size uniformity. Nevertheless, most of the available monodisperse colloidal materials are spherical, as the minimization of the interfacial free energy strongly drives a particle to adopt such a shape. [1] This strongly limits the number of new structures which can be engineered by using these colloids as building blocks. For instance, the crystallization of spherical colloids into three-dimensional periodic lattices has recently allowed the emergence of a very active field of research—photonic colloidal crystals, known as artificial opals. Nevertheless, the light diffraction properties of these crystals are rather limited because of their face-centered cubic lattice, which results from the packing of spheres. It has been predicted that crystals with a lower degree of symmetry, such as the diamond lattice, can exhibit a full photonic bandgap. To build such photonic crystals, well-defined colloids with nonspherical shapes are required. Van Blaaderen recently introduced the elegant term of “colloidal molecules”, [2] which takes into account that spherical colloids can be treated as if they were atoms and that molecules can form more complex materials than can atoms. Therefore, the reproducible fabrication of large amounts of colloids that have a good uniformity in