Optical absorbers based on strong interference in ultra-thin films

TL;DR

This paper reviews recent developments in ultra-thin film optical absorbers that leverage interference effects, offering practical, scalable solutions for various optical applications without complex nanostructuring.

Contribution

It introduces the concept of ultra-thin-film interference-based absorbers, highlighting their theoretical foundation and diverse applications, advancing scalable optical absorber design.

Findings

Achieved high absorption with films much thinner than the wavelength

Demonstrated applications in color coatings and photovoltaics

Provided theoretical insights into loss-induced phase shifts

Abstract

Optical absorbers find uses in a wide array of applications across the electromagnetic spectrum, including photovoltaic and photochemical cells, photodetectors, optical filters, stealth technology, and thermal light sources. Recent efforts have sought to reduce the footprint of optical absorbers, conventionally based on graded structures or Fabry-Perot-type cavities, by using the emerging concepts of plasmonics, metamaterials, and metasurfaces. Unfortunately, these new absorber designs require patterning on subwavelength length scales, and are therefore impractical for many large-scale optical and optoelectronic devices. In this article, we summarize recent progress in the development of optical absorbers based on lossy films with thicknesses significantly smaller than the incident optical wavelength. These structures have a small footprint and require no nanoscale patterning. We outline the theoretical foundation of these absorbers based on "ultra-thin-film interference", including the concepts of loss-induced phase shifts and critical coupling, and then present several applications, including ultra-thin color coatings, decorative photovoltaics, high-efficiency photochemical cells, and infrared scene generators.