Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry

Abstract

A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal–insulator–metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850 nm based on Ag (25 nm) and MgF$_{2}$ (75–250 nm). Maximum spectral transmittance is measured at ∼70% with a $\textit{Q}$-factor of ∼20.Engineering and Physical Sciences Research Council (EPSRC) (EP/L015455/1); Cambridge Commonwealth, European and International Trust