Simple three-layer silver-glass-silver optical structure serves as narrowband spectral filter
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.
REFERENCE:
1. Zhongyang Li et al., ACS Photonics (2015); doi: 10.1021/ph500410u
John Wallace | Senior Technical Editor (1998-2022)
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.