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

Disordered one-dimensional photonic bandgap (PBG) structures could prove useful in designing broadband reflectors capable of filtering chosen polarizations of incoming light. By capitalizing on the similarities between defects and disorder, it is possible to construct a 1D PBG structure such that the layers are non-uniform but the structure can retain its most novel properties. This is done by allowing the thickness of the layers in the structure to deviate uniformly around an average thickness by a preselected amount of deviation. A mathematical model using the Transfer Matrix Method for simulation has been previously constructed by this group. This model has been verified using FDTD simulation as well. The PBG structure was then fabricated consisting of TiO2 deposited by electron-beam physical vapor deposition (e-beam PVD) first at normal incidence and then at a 70 degrees oblique angle. This pattern was repeated to create six bilayers of TiO2 films. This alternating pattern gives rise to the novel structure of a PBG structure by creating a repeating pattern of amorphous and biaxial, columnar, birefringent TiO2, which is analogous to using two different materials. Through testing using a polarizer, analyzer, and HeNe laser with a wavelength of 632.8 nm, it has been found that the sample does in fact match well with the expected theoretical results and acts as a broadband reflector for the TM polarization designed for a 70 degrees incidence angle. The average layer thickness of the fabricated TiO2 PBG is 22.7 nm.