12-fold Photonic Quasicrystals Research Articles

Enhancing light extraction efficiency of polymer light-emitting diodes with a 12-fold photonic quasi crystal

This work demonstrates the enhancement of light extraction of polymer light-emitting diodes (PLEDs) by incorporating a 12-fold photonic quasi crystal (PQC) in the device structure. Multi-exposure two-beam interference technique combined with inductively coupled plasma etching was employed to pattern a 12-fold PQC structure on the ITO film on a glass substrate of the diode. The air-hole coverage (AHC) and etching depth dependences of the light emitting performance of the 12-fold PQC patterned PLEDs were investigated. For AHC within the range between 6.4% and 32.3%, a nearly constant enhancement of the luminance efficiency of the PQC PLEDs was observed. On the other hand, the light emitting performance of the PQC PLEDs is very sensitive to the etching depth. The photoluminescence intensity of the PQC PLEDs increases monotonically with the etching depth. In contrast, the electro luminance efficiency shows a non-monotonic dependence on etching depth with a maximum occurring at 55 nm etching depth. The maximum improvement of luminance efficiency of the 12-fold PQC PLEDs reaches nearly 95% compared with an un-patterned PLED at an injection current of 110 mA.

Fourier–Bessel analysis of localized states and photonic bandgaps in 12-fold photonic quasi-crystals

A Fourier-Bessel (FB) basis is used to solve two-dimensional (2D) cylindrical Maxwell's equations for localized states within dielectric structures that possess rotational symmetry. The technique is used to determine the wavelengths and profiles of the stationary states supported by the structure and identify the bandgaps. 12-fold quasi-crystals for the TE and TM polarizations are analyzed. Since the FB approach with 2D photonic crystals in this fashion is new, the accuracy of the results is confirmed using finite-difference time-domain simulations.

Q-Factor Microcavity Design Based on 12-Fold Photonic Quasicrystals

A microcavity based on 12-fold photonic quasicrystals is achieved by the aid of alteration in the proposed structure. The central air hole is missed, and the three nearest surrounding holes radiuses and positions are modified in order to optimize the Q-factor. In addition, special fine variations are imposed on the mentioned parameters to shift the resonant wavelength in the 1.55- and 1.31-μm window bands. One of the predominant features of this microcavity structure is its capability of obtaining a Q-factor of about 2 × 106 in the 1.55-μm wavelength window band, which is the most desirable wavelength in the optical telecommunication.

Multiple slow light bands in photonic crystal coupled resonator optical waveguides constructed with a portion of photonic quasicrystals

Coupled resonator optical waveguides (CROWs) in complex two-dimensional (2D) photonic crystals (PCs) constructed with a portion of 12-fold photonic quasicrystals (PQs) are proposed. We show that enhanced transmission and slow light can be simultaneously achieved in such waveguides as well as general CROWs. Moreover, due to higher degree of flexibility and tunability of PQs for defect mode properties compared to conventional periodic PCs, multiple slow light bands can be flexibly obtained in CROWs constructed with complex 2D PCs. Our results may lead to the development of a variety of novel ultracompact devices for photonic integrated circuits.

Efficiency Improvement of GaN-Based LEDs With a $ \hbox{SiO}_{2}$ Nanorod Array and a Patterned Sapphire Substrate

The enhancement of light extraction from GaN-based light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS) and a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 12-fold photonic quasi-crystal (PQC) structure using nanoimprint lithography is presented. At a driving current of 20 mA on transistor-outline-can package, the light output powers of LED with a PSS and LED with a PSS and a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> PQC structure are enhanced by 35% and 48%, compared with the conventional LED. In addition, the higher output power of the LED with a PSS and a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> PQC structure is due to better reflectance on PSS and higher epitaxial quality on an n-GaN using a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 12-fold PQC structure pattern. These results provide promising potential to increase output powers of commercial light-emitting devices.

Improved Light Output Power of GaN-Based Light-Emitting Diodes Using Double Photonic Quasi-Crystal Patterns

The enhancement of light extraction from GaN-based light-emitting diodes (LEDs) with a double 12-fold photonic quasi-crystal (PQC) structure using nanoimprint lithography is presented. At a driving current of 20 mA on a transistor-outline-can package, the light output power of an LED with a nanohole patterned sapphire substrate (NHPSS) and an LED with a double PQC structure are enhanced by 34% and 61%, compared with the conventional LED. In addition, the higher output power of the LED with the double PQC structure is due to better reflectance on NHPSS and higher scattering effect on p-GaN surface using a 12-fold PQC structure pattern. These results provide promising potential to increase the output powers of commercial light-emitting devices.

Interaction of fast electron beam with photonic quasicrystals

The interactions of two-dimensional 10-fold and 12-fold photonic quasicrystals with a moving electron beam have been studied by using the multiple-scattering method. The electron energy loss spectroscopy (EELS) and three-dimensional local density of states in these systems have been calculated. Some three-dimensional localized states in these defect-free two-dimensional systems have been found. It has been demonstrated that these localized states can be explored by means of the EELS.

Enhanced light output power of GaN-based vertical-injection light-emitting diodes with a 12-fold photonic quasi-crystal by nano-imprint lithography

GaN-based thin-film vertical-injection light-emitting diodes (VLEDs) with a 12-fold photonic quasi-crystal (PQC) by nano-imprint lithography (NIL) are fabricated and presented. At a driving current of 20 mA and with a chip size of 350 µm × 350 µm, the light output power of our thin-film LED with a 12-fold PQC structure reaches 41 mW. This result is an enhancement of 78% when compared with the output power of a VLED without a PQC structure. In addition, the corresponding light radiation pattern shows a narrower beam shape due to the strong guided light extraction effect by the formed PQC structure in the vertical direction.

Two-dimensional photonic crystals constructed with a portion of photonic quasicrystals

Photonic quasicrystals (PQs) can produce interesting photonic properties but the lack of periodicity in structures makes exact prediction on their photonic band structures (PBSs) a fundamental challenge currently. Here, we propose a kind of complex two-dimensional photonic crystal (PC) structures constructed with a small portion of different PQs for the purposes of overcoming the difficulty of numerical calculations on the PBSs but maintaining photonic properties of the original PQs owned. Theoretically calculated results on PBSs of the complex PC with a local feature consistent with 12-fold rotational symmetry show that, in the cases of dielectric cylinders in air, air-holes in a dielectric, and metal cylinders in air, respectively, the complex PC can indeed produce similar photonic properties of the original 12-fold PQ such as uniform or isotropic PBGs under much lower dielectric contrast etc. The complex PCs can be constructed with the local parts of n-fold symmetric PQs and should provide a way for creating novel photonic functional materials.

FDTD analysis of out-of-plane propagation in 12-fold photonic quasi-crystals

The out-of-plane propagation characteristics of an infinitely extended 12-fold photonic quasi-crystal structure is modeled using the FDTD technique. The quasi-crystal pattern is designed using the dual beam multiple exposure holographic lithography system previously reported. Simulations indicate that two types of mode families are possible; “bandgap guided” and; “index guided”. Results are presented showing mode profiles; effective index versus propagation constant and wavelength plots; and modal attenuation due to power leakage. Potential applications include a new novel micro-structured optical fiber.