Inductive grid filters for rejection of infrared radiation

Abstract

Inductive grid filters are metallic mesh structures, which reject long wavelengths but transmit short wavelengths. Our interest is in filters with the rejection cut-off at around 1 μm. In this region the finite conductivity of metals must be considered. An extensive theoretical investigation is carried out by rigorous diffraction theory to determine the best choice of metal and the influence of the grid parameters on the spectral transmittance of the filter. Experimental results with nickel and gold grids fabricated on dielectric substrates are presented. Their fabrication process involves thin-film deposition, electron beam lithography, reactive ion etching and electroplating. The optical characterization results performed with spectrophotometry are in reasonable agreement with the theoretical predictions.