Design of cubic-phase optical elements using subwavelength microstructures.

We describe a design methodology for synthesizing cubic-phase optical elements using two-dimensional subwavelength microstructures. We combined a numerical and experimental approach to demonstrate that by spatially varying the geometric properties of binary subwavelength gratings it is possible to produce a diffractive element with a cubic-phase profile. A test element was designed and fabricated for operation in the LWIR, approximately lambda=10.

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.

Modulating dispersion properties of low index photonic crystal structures using microfluidics.

We present a technique for manipulating the dispersive properties of low index periodic structures using microfluidic materials that fill the lattice with various fluids of different refractive indices. In order to quantify the modulation of the optical properties of the periodic structure we use Equi-frequency contours (EFC) data to calculate the frequency dependant refractive index and the refractive angle. We further introduce various types of defects by selectively filling specific lattice sites and measuring the relative change in the index of refraction.

Design of two-dimensional polarization-selective diffractive optical elements with form-birefringent microstructures.

We describe a design methodology for synthesizing polarization-sensitive diffractive optical elements based on two-dimensional form-birefringent microstructures. Our technique yields a single binary element capable of producing independent phase transformations for horizontally and vertically polarized illumination. We designed two elements for operation at 10.

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.

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.

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.

Fabrication and characterization of three-dimensional silicon tapers.

We present the fabrication of 3D adiabatically tapered structures, for efficient coupling from an optical fiber, or free-space, to a chip. These structures are fabricated integrally with optical waveguides in a silicon-on-insulator wafer. Fabrication involves writing a single grayscale mask in HEBS glass with a high-energy electron beam, ultra-violet grayscale lithography, and inductively coupled plasma etching.

Optimizing bending efficiency of self-collimated beams in non-channel planar photonic crystal waveguides.

In this paper, we propose a device to bend light in non-channel planar photonic crystal (PhC) waveguides using the self-collimation phenomenon. The mode distribution in a non-channel planar PhC waveguide is investigated in detail in order to help understand the proposed bending mechanism. Three-dimensional finite-difference time-domain simulations show an over 80% bending efficiency for a 90 degree bend.

High transmission through waveguide bends by use of polycrystalline photonic-crystal structures.

A hybrid photonic-crystal structure is presented as a candidate for enhancing transmission through sharp photonic-crystal waveguide bends built on a perforated dielectric slab. This structure, which we refer to as a polycrystalline structure, combines two photonic-crystal lattices. Polycrystalline photonic-crystal structures offer the ability to minimize reflections as well as mismatches that a propagating wave might encounter while undergoing a sharp corner or a discontinuity between different waveguide sections.

Tunable photonic crystal microcavities.

We present a method for tuning a photonic crystal microcavity by modulating the index of refraction of the lattice sites within and surrounding the microcavity. The index of refraction can be actively modulated after infiltrating anisotropic liquid crystals into a two-dimensional photonic crystal lattice of air cylinders in silicon. We analyze the Q-factors and resonance frequencies of a tunable photonic crystal microcavity by considering various methods of index modulation.