Large-area, Lithography-Free Super Absorbers and Color Filters at Visible Frequencies Using Ultrathin Metallic Films

TL;DR

This paper presents a lithography-free, large-area method for creating high-performance visible-frequency super absorbers and color filters using ultrathin metallic films within asymmetric Fabry-Perot cavities, overcoming nanofabrication challenges.

Contribution

It introduces a novel, scalable design for optical filters based on ultrathin metallic films and asymmetric cavities, achieving high absorption and narrow-band color filtering without nanofabrication.

Findings

Achieved 97% absorption with a 17 nm bandwidth in super absorbers.

Demonstrated color filters with 60% peak transmission and 40 nm bandwidth.

Performance surpasses nanostructure-based filters in certain metrics.

Abstract

Plasmonic materials and metamaterials have been widely utilized to achieve spectral transmission, reflection and absorption filters based on localized or delocalized resonances arising from the interaction of photons with nanostructured materials. Realization of visible-frequency, high-performance, large-area, optical filters based on nanoplasmonic materials is rather challenging due to nanofabrication related problems (cost, fabrication imperfection, surface roughness) and optical losses of metals. Here, we propose and demonstrate large-area perfect absorbers and transmission filters that overcome difficulties associated with the nanofabrication using a lithography-free approach. We also utilize and benefit from the optical losses in metals in our optical filter designs. Our resonant optical filter design is based on a modified, asymmetric metal-insulator-metal (MIM) based Fabry-Perot cavity with plasmonic, lossy ultra-thin (~30 nm) metallic films used as the top metallic layer. We demonstrated a narrow bandwidth (~17 nm) super absorber with 97% maximum absorption with a performance comparable to nanostructure/nanoparticle-based super absorbers. We also investigated transmission (color) filters using ultra-thin metallic films, in which different colors can be obtained by controlling the dielectric spacer thickness. With performance parameters of transmission peak intensity reaching 60% and a narrow-band of ~ 40 nm, our color filters exceed the performance of widely studied plasmonic nanohole array based color filters. Proposed asymmetric Fabry-Perot cavities using ultra-thin metallic films could find applications in spectrally selective optical (color and absorber) filters, optoelectronic devices with controlled bandwidth such as narrow-band photodetectors, and light-emitting devices.