Photonic Crystal Elements
Overview
A photonic crystal is an anisotropic optical multilayer film. It is possible to deposit an optical thin film with regions where the effective index differs by patterning a substrate. In this way it is possible to fabricate a polarizer or a wave-plate.
Because the functionality of the element is achieved by the periodic structure of
the crystal, there is the possibility to engineer the operating wavelength.
Typically the limit of the bandwidth is 20% of the operating wavelength.
For laser applications, the extinction ratio over a narrow band can be controlled by increasing the number of deposited layers.
A 1/4 wave-plate, 1/2 wave-plate etc. can be achieved by the deposition of a multilayer film of several microns. It is also possible to phase match two or more wavelengths using a photonic band gap etc.
