Fano Resonance Optical Coatings (FROCs)

A multi-institutional team has created an optical coating capable of reflecting and transmitting the same wavelength simultaneously. Fano Resonance Optical Coatings is the name given to a new class of optical coatings (FROCs).

Previously, optical coatings could only reflect certain wavelengths of light or better transmit certain wavelengths through them. Thermal and photovoltaic bands of the solar spectrum can now be separated using new technology. The advancement could significantly improve the efficiency of solar energy devices that use hybrid thermal-electric power generation. By separating those bands, photovoltaic cells can avoid overheating.

The researchers reported that the Fano Resonance Optical Coating technology could increase the life of a photovoltaic cell sixfold. In practice, the remaining spectra are absorbed as thermal energy, which can be used for various purposes such as energy storage, electricity generation, solar-powered water sanitation, or heating a water supply.

In search of a simpler method, the researchers investigated the use of optical coatings to exploit Fano resonance. They used a 15-nm-thick germanium film on a metal surface to absorb a wide range of wavelengths. The design was combined with a cavity that supported a narrow-band resonance. The coupled cavities demonstrated Fano resonance, which could reflect a very narrow band of light.

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