1. THE PHYSICS OF TUNABLE IMAGING

A rich variety of physical phenomena can isolate a finite spectral band: absorption, scattering, diffraction, evanescence, birefringence, acousto-optics, single layer and multi-layer interference, multi-path interferometry, polarizability, and so on. Most of the available optical filter technologies are listed below:

linear / circular variable filter

multi-layer dielectric filter

Fabry-Perot interferometer

Michelson interferometer

acousto-optic filter

solid etalon filter

solid Michelson filter

generalized resonant grating filter

sub-lambda evanescent grating filter

volume phase holographic grating filter

Lyot-Öhman filter

generalized Lyot filter

generalized Solc filter

liquid crystal filter

There is a bewildering array of future possibilities, including tunable crystal lattice structures, and many possible variants on the above technologies. Here, we focus on a few key technologies.