Visible narrowband transmissive filter of many different colors consist of a simple three-layer silver-glass-silver structure.
Researchers at Northwestern University (Evanston, IL) have created a simple, low-cost metal-dielectric color-filter structure that contains no nanostructuring, yet performs better than existing plasmonic nanohole-array color filters.1 The metal-insulator-metal (MIM) Fabry-Perot cavity is made of glass and silver, is asymmetric, and has a lossy 30-nm-thick silver film as the top layer. The transmissive color filter has a bandwidth of about 40 nm and a peak transmittance of 60%; an absorptive version with a thicker bottom layer has a narrowband (17 nm) absorption of 97%. The optical loss of the top silver layer is essential to the device's operation.
The transmissive version is clearly useful for spectral filtering; the absorptive version could be useful in narrowband photodetectors and light-emitting devices. Both bypass the complications of nanotechnology (or many-layered dielectric film stacks).
The researchers are developing similar structures out of aluminum and glass intended for use in the ultraviolet.
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.
