Controlling the spectral transmission, reflection, and absorption properties of optical structures is of great interest for many applications in photonics. Particularly, perfect absorbers over a wide frequency (wavelength) range are desirable for thin-film thermal emitters, thermo-solar cells, photodetectors, and smart windows. Up to date, several mechanisms have been proposed to achieve nearly 100% absorption in various frequency ranges of the electromagnetic spectrum; starting from microwaves to near infrared (NIR) and visible. One of the first demonstrations of a structure that was absorbing with nearly 100% efficiency was proposed by Landy et al. in 2008,[1] where metamaterial resonator arrays were used to achieve narrowband and highly resonant absorption of GHz and THz waves. The narrowband character of the resonances can be an advantage when absorbers with high quality factor are required and wavelength selectivity is desirable. However, there are many applications that need broadband absorption. To this end great efforts have been made during the last decade, for instance by mixing multiple resonances in a many-fold resonator, which can lead to, e.g., dual band[2] or multiband[3-9] resonant absorption. Unfortunately fabrication of these structures requires sophisticated techniques such as micro- or nano-lithography, severely limiting their scalability and increasing the cost of the absorber.

Peer Reviewed