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Hyperbolic Metamaterial Filter for Angle-independent TM-Transmission in Imaging Applications

With conventional narrowband filters, the center-wavelength of the narrow transmission band undergoes large shifts as the angle of incident light changes. In this project, we designed and experimentally verified a type of hyperbolic metamaterial Bragg stack that eliminates, or vastly reduces, this angle-of-incidence dependence (i.e., dispersion) of the transmission band for TM polarized beam. The filter developed in this project is composed of array of subwavelength sized metal wires vertically penetrating in the dielectric layers of the Bragg stack. We first discuss the physical reasons why such a structure is expected to minimize dispersion, then we performed detailed electromagnetic modeling, fabrication of proof-of-concept structures, and optical testing of the structures. The filter is fabricated by CMOS fabrication techniques and optical characterized using Fourier-transform infrared spectroscopy. Both simulated and experimental data show that narrow band transmission filters can be designed such that the center-wavelength of the transmission peak for TM polarized incident light does not change as the angle of incidence of an incoming beam changes. These types of narrowband notch filters have been used in many sensing and imaging applications, including remote sensing and hyperspectral imaging.