Chien C. Chang

Connected hexagonal photonic crystals with largest full band gap

A two-dimensional photonic crystal with a large full band gap has been designed, fabricated, and characterized. The photonic crystal design was based on a calculation using inverse iteration with multigrid acceleration. The fabrication of the photonic crystal on silicon was realized by the processes of electron-beam lithography and inductively coupled plasma reactive ion etching. It was found that the hexagonal array of circular columns and rods has an optimal full photonic band gap. In addition, we show that a larger extraction of light from our designed photonic crystal can be obtained when compared with the frequently used photonic crystals reported previously. Our designed PC structure therefore should be very useful for creating highly efficient optoelectronic devices.

Monte Carlo Simulation of Optical Properties of Phosphor-Screened Ultraviolet Light in a White Light-Emitting Device

In this paper, we study the optical properties of phosphor-screened ultraviolet light emitted by a quantum well through a chamber. The chamber contains randomly distributed red, blue and green phosphors, and is top-covered with a layer of omnidirectional photonic bandgap material. A Monte Carlo ray tracing method is developed to model the absorption, reflection and transmission for the excited radiation of the ultraviolet light as well as the visible light by the individual phosphor particles. The efficiency of emitting white light by synthesizing the visible light through the top substrate is investigated with respect to the weight ratio, the size of phosphor particles, the dimension of the chamber and the reflectivity of the side wall and the bottom substrate.

Numerical Study of Three-Dimensional Photonic Crystals with Large Band Gaps

The study presents a finite difference formulation for efficiently computing band structures of three-dimensional photonic crystals. First of all, we will show how to correctly discretize the doubl...

Two Classes of Photonic Crystals with Simultaneous Band Gaps

In this study, we consider band structures of two classes of photonic crystals with two geometric parameters. The first class has a square lattice and is studied for dielectric contrast, centered at e/e0=11.4 (GaAs-air). The second class has a hexagonal lattice and is studied for dielectric contrast, centered at e/e0=13 (silicon-air). These examples have the following feature: the optimal (and largest) full band gap is obtained when both band gaps for E and H polarizations have the same (simultaneous) band edges. In addition, photonic crystals with two geometric parameters typically have much larger optimal band gaps than their counterparts with one geometric parameter.

Augmented coupling interface method for solving eigenvalue problems with sign-changed coefficients

In this paper, we propose an augmented coupling interface method on a Cartesian grid for solving eigenvalue problems with sign-changed coefficients. The underlying idea of the method is the correct local construction near the interface which incorporates the jump conditions. The method, which is very easy to implement, is based on finite difference discretization. The main ingredients of the proposed method comprise (i) an adaptive-order strategy of using interpolating polynomials of different orders on different sides of interfaces, which avoids the singularity of the local linear system and enables us to handle complex interfaces; (ii) when the interface condition involves the eigenvalue, the original problem is reduced to a quadratic eigenvalue problem by introducing an auxiliary variable and an interfacial operator on the interface; (iii) the auxiliary variable is discretized uniformly on the interface, the rest of variables are discretized on an underlying rectangular grid, and a proper interpolation between these two grids are designed to reduce the number of stencil points. Several examples are tested to show the robustness and accuracy of the schemes.

Phononic Band Gaps of Elastic Periodic Structures: A Homogenization Theory Study

In this study, we investigate band structures of phononic crystals with particular emphasis on the effects of the mass density ratio and of the contrast of elastic constants. The phononic crystals consist of arrays of different media embedded in a rubber or epoxy. It is shown that the density ratio rather than the contrast of elastic constants is the dominant factor that opens up phononic band gaps. The physical background of this observation is explained by applying the theory of homogenization to investigate the group velocities of the low-frequency bands at the center of symmetry Γ.Copyright