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 850nm based on Ag (25nm) and MgF2 (75-250nm). Maximum spectral transmittance is measured at ∼70% with a Q-factor of ∼20.
Highlights
Optical transmission filters, linear variable bandpass filters (LVBFs), are crucial optical elements in a number of different applications including astronomy and hyper-spectral imaging [1]
Alternatives include holographic color filters [6], but these suffer from inherent diffraction orders and, again, require expensive lithographic processes
In this paper, using fabrication methodology based on the modification of conventional metal evaporation techniques, we demonstrate LVBFs based on ultra-thin-film MIM cavities at first-order resonance, which include a thin (25 nm) top–bottom metallic (Ag) layer coupled to a dielectric cavity composed of transparent MgF2 (75–250 nm)
Summary
Linear variable bandpass filters (LVBFs), are crucial optical elements in a number of different applications including astronomy and hyper-spectral imaging [1]. Conventional LVBF fabrication processes include reflow of photographically patterned layers of resist [2,3], gray-scale lithography [4], and mechanically moving multiple graded masks [5]. These techniques suffer drawbacks including high cost, complexity, and processing time. Alternatives include holographic color filters [6], but these suffer from inherent diffraction orders and, again, require expensive lithographic processes. Plasmonicenhanced optical elements have been investigated [7,8,9,10,11,12], yet they inherently suffer damping (loss) mechanisms and likewise require lithographic processes
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