Surface plasmon tunable filter and spectrometer-on-a-chip

The surface plasmon tunable filter (SPTF) is a new technology invented at the Jet Propulsion Laboratory. When white light is incident on a metal/air/metal structure, under appropriate conditions, surface plasmon waves are excited at one metal/air material interface. Those photons in the surface plasmon resonance wavelength range will be converted into the energy of free electrons in the metal, then coupled into the other metal film which re-radiates light at the identical resonant wavelength. This surface plasmon resonance depends on the dielectric constant of the metal and the thickness of the air gap. When the thickness of the air gap changes, the surface plasmon resonance spectrum shifts from one wavelength to another, and the device functions as a tunable filter. The SPTF is a light weight, low power device, which can be integrated with a solid state image sensor to form a spectrometer-on-a-chip. Theoretical calculation has shown that this image spectrometer can also work in JR range up to at least 10 mu m.