title: Gradient-index narrow-bandpass filter fabricated with glancing-angle deposition.
abstract: Glancing-angle deposition (GLAD) is a fabrication method capable of producing thin films with engineered nanoscale porosity variations. GLAD can be used to create optical thin-film interference filters from a single source material by modification of the film refractive index through control of film porosity. We present the effects of introducing a layer of constant low density into the center of a rugate thin-film filter fabricated with the GLAD technique. A rugate filter is characterized by a sinusoidal refractive-index profile. Embedding a layer of constant refractive index, with a thickness equal to one period of the rugate index variation, causes a narrow bandpass to appear within the filter's larger stop band. Transmittance measurements of such a gradient-index narrow-bandpass filter, formed with titanium dioxide, revealed an 83% transmittance peak at a vacuum wavelength of 522 nm, near the center of the stop band, with a FWHM bandwidth of 15 nm.
authors.affiliation: Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada. vanpopta@ualberta.ca
authors.forename: Andy C
authors.initials: AC
authors.lastname: van Popta
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Hawkeye
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Sit
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Brett