Photonic Crystal Technology Introduction

1. An Introduction to Photonic Crystals

A photonic crystal is a periodic structure of materials with differing refractive indices. Therefore, the optical multilayer films widely used as anti-reflection films etc. for the surface of television monitors, glasses and other optical components can be considered to be one dimensional photonic crystals. However, generally the term photonic crystal refers to two dimensional and three dimensional structures.
The pitch of the structure is usually chosen such that it is half the wavelength of the light for which the element is designed for. Typically, photonic crystals used in the visible optical region are designed and fabricated so that the period is about 300nm.

Like optical multilayer films, photonic crystals are used to control optical transmission, reflection and refraction characteristics. Using 2D and 3D photonic crystals it is possible to control the propagation of light at arbitrary angles of incidence and not only the light normally incident as is the case for conventional optical films.
Further, using photonic crystals, it is possible to achieve optical functionality not possible using conventional optical materials. Examples of such functionality are introduced briefly on the functionality page.

2. Photonic Crystal Structures

Two different optical materials (or one optical material and air) periodically arranged as above constitute a photonic crystal. A periodic one dimensional structure can easily be fabricated by sequential deposition of two materials. Though, various structures and fabrication methods have been proposed for photonic crystals of two dimensions and three dimensions, these are considerably more difficult to fabricate.

The wood pile photonic crystal was one of the first three dimensional photonic crystals to be proposed. The origin of the name is the manner in which the optical material is piled up to form a support structure similiar to that of a well. The fabrication process of piling up the "logs" is complex and the use of semiconductor fabrication processes is necessary. The opal type photonic crystal stacks beads. These techniques generally require a large amount of time, though there are techniques such as self-assembly; where grains of an optical material are placed in a liquid.

Our autocloned photonic crystal is composed of a patterned multilayer film, and is the only, multi-dimensional, photonic crystal that can be fabricated by conventional sputtering deposition, and established mass production technologies.