Caihua Chen

Thin film silicon solar cell design based on photonic crystal and diffractive grating structures

In this paper we present novel light trapping designs applied to multiple junction thin film solar cells. The new designs incorporate one dimensional photonic crystals as band pass filters that reflect short light wavelengths (400 - 867 nm) and transmit longer wavelengths(867 -1800 nm) at the interface between two adjacent cells. In addition, nano structured diffractive gratings that cut into the photonic crystal layers are incorporated to redirect incoming waves and hence increase the optical path length of light within the solar cells. Two designs based on the nano structured gratings that have been realized using the scattering matrix and particle swarm optimization methods are presented. We also show preliminary fabrication results of the proposed devices.

Dispersion-based optical routing in photonic crystals

We present and experimentally validate self-collimation in planar photonic crystals as a new means of achieving structureless confinement of light in optical devices. We demonstrate the ability to arbitrarily route light by exploiting the dispersive characteristics of the photonic crystal. Propagation loss as low as 2.17 dB/mm is observed, and proposed applications of these devices are presented.

Self-collimation in photonic crystal structures: a new paradigm for applications and device development

In this paper, we report on the development of the self-collimation phenomenon in photonic crystal structures for integrated optics applications. In addition, detailed numerical analysis, design procedures, fabrication and characterization techniques are included. Applications presented in this paper include: channelless waveguiding, orthogonal bending of light, tunable beam splitter, all-optical analog-to-digital converter, reconfigurable optical switch, chemical/gas sensor and a three-dimensional optical interconnect bus.

Plane-wave expansion method for calculating band structure of photonic crystal slabs with perfectly matched layers

We present a new algorithm for calculation of the band structure of photonic crystal slabs. This algorithm combines the plane-wave expansion method with perfectly matched layers for the termination of the computational region in the direction out of the plane. In addition, the effective-medium tensor is applied to improve convergence. A general complex eigenvalue problem is then obtained. Two criteria are presented to distinguish the guided modes from the PML modes. As such, this scheme can accurately determine the band structure both above and below the light cone. The convergence of the algorithm presented has been studied. The results obtained by using this algorithm have been compared with those obtained by the finite-difference time-domain method and found to agree very well.

High-efficiency coupling structure for a single-line-defect photonic-crystal waveguide

We present the design and fabrication of a planar structure for coupling light from a multimode feed waveguide into a single-line-defect photonic-crystal waveguide. Finite-difference time-domain calculations predict a coupling efficiency of greater than 90%, and preliminary experimental results indicate successful coupling through a single-line-defect photonic-crystal waveguide. Device design, fabrication, and characterization are presented.

Dispersion-based beam splitter in photonic crystals

A novel implementation of a dispersion-based beam splitter in a photonic crystal (PhC) is proposed. The beam splitter consists of two periodic structures: a nonchannel dispersion-guiding region and a splitting structure operating inside the photonic bandgap. The dispersion-guiding PhC structure is used to route the optical wave by exploiting the dispersion properties of the lattice. An arbitrary power ratio between the output beams can be achieved by varying the parameters of the splitting structure. Within the studied range of splitting structures, high output power was observed and verified experimentally.

Analysis of splitters for self-collimated beams in planar photonic crystals

In this paper, we present methods for beam splitting in a planar photonic crystal, where the light is self-guided as dictated by the selfcollimation phenomenon. We present an analysis of a one-to-two and one-to-three beam splitter in a self-guiding photonic crystal lattice and validate our design and simulations with experimental results. Moreover, we present the first one-to-three splitter in a self-guiding planar photonic crystal. Additionally, we discuss the ability to tune the properties of these devices and present initial experimental results.

Thin infrared imaging systems through multichannel sampling

The size of infrared camera systems can be reduced by collecting low-resolution images in parallel with multiple narrow-aperture lenses rather than collecting a single high-resolution image with one wide-aperture lens. We describe an infrared imaging system that uses a three-by-three lenslet array with an optical system length of 2.3 mm and achieves Rayleigh criteria resolution comparable with a conventional single-lens system with an optical system length of 26 mm. The high-resolution final image generated by this system is reconstructed from the low-resolution images gathered by each lenslet. This is accomplished using superresolution reconstruction algorithms based on linear and nonlinear interpolation algorithms. Two implementations of the ultrathin camera are demonstrated and their performances are compared with that of a conventional infrared camera.

Revised plane wave method for dispersive material and its application to band structure calculations of photonic crystal slabs

In this letter we present a revised formulation of the plane wave method (PWM) for the band structure calculation of photonic crystals. In comparison to the conventional PWM, the formulation in this letter allows for modeling of dispersive material. One application of the presented method is for band structure calculations of photonic crystal slabs. While a thin photonic crystal slab is considered, a full three-dimensional (3D) problem can be reduced to a two-dimensional one by using the effective index method. However, the obtained effective index of such a slab is frequency dependent. The revised PWM is then applied to solve this problem. The results obtained using this algorithm have been compared with those using a full 3D finite-difference time-domain method and found to agree very well.

Photonic Crystal Structures and Applications: Perspective, Overview, and Development

In this paper, we present an overview of milestone achievements in the research and development of photonic crystal structures and their perspective applications. We highlight challenges in the analysis techniques, device design, efficient coupling techniques, and fabrication and characterization techniques for both planar and three-dimensional structures. We discuss extensively progress to date to overcome various aspects in the available modeling and simulation tools as well as the necessary fabrication procedures to produce functional photonic crystal structures and devices. Hence, the goal of the work presented in this paper is to present key building blocks, which will in turn facilitate the full utilization of the unique spatial and temporal properties of photonic crystal structures