Design, Fabrication, and Characterization of a Disordered, One-Dimensional, Broadband Photonic Bandgap Structure

摘要

Disordered one-dimensional photonic bandgap (PBG) structures could prove useful in designing broadbandreflectors capable of filtering chosen polarizations of incoming light. By capitalizing on the similarities betweendefects and disorder, it is possible to construct a 1D PBG structure such that the layers are non-uniform but thestructure can retain its most novel properties. This is done by allowing the thickness of the layers in the structureto deviate uniformly around an average thickness by a preselected amount of deviation. A mathematical modelusing the Transfer Matrix Method for simulation has been previously constructed by this group. This model hasbeen verified using FDTD simulation as well. The PBG structure was then fabricated consisting of TiO_2 depositedby electron-beam physical vapor deposition (e-beam PVD) first at normal incidence and then at a 70o obliqueangle. This pattern was repeated to create six bilayers of TiO_2 films. This alternating pattern gives rise to the novelstructure of a PBG structure by creating a repeating pattern of amorphous and biaxial, columnar, birefringentTiO2 ,which is analogous to using two different materials. Through testing using a polarizer, analyzer, and HeNelaser with a wavelength of 632.8 nm, it has been found that the sample does in fact match well with the expectedtheoretical results and acts as a broadband reflector for the TM polarization designed for a 70º incidence angle.The average layer thickness of the fabricated TiO_2 PBG is 22.7 nm.