Actively Tunable Photonic Device Enables Multispectral Infrared Camouflage

Abstract

Researchers at the University of Central Florida have designed an innovative adaptive infrared (IR) camouflage system that can operate at any wavelength in the technologically relevant, midwave IR (3?5 ?m) and longwave IR (8?12 ?m) bands. The plasmonic nanostructured system design offers a faster, more efficient way to encode information and provides spectral selectivity, which is unavailable in current adaptive IR camouflage technologies. By using multispectral coupling mechanisms and constraining key structural parameters, the new system enables independent tuning of infrared resonances while keeping visible properties invariant. Such capabilities promote advancements in IR tagging, camouflaging and anticounterfeiting.

Technical Details

The cavity-coupled absorber architecture of the UCF system consists of a complementary gold hole/disk array; a tri-layered cavity spacer of silicon dioxide (SiO2), vanadium dioxide (VO2) and an SU-8 polymer; and a reflective back mirror. The system actuates adaptive camouflage by exploiting the semiconductor-to-metal phase transition in the VO2, which modifies the reflection spectra of the system. Thus, depending on the phase of the VO2 layer, the cavity length dynamically changes. In its semiconducting state, VO2 is transparent to IR so that incident light couples to the entire cavity length. However, in the metallic state, VO2 behaves like a mirror and shortens the cavity length by isolating the SiO2 layer from the system.

To demonstrate the system?s multispectral capabilities, researchers encoded an image into a designer-imprinted surface made using a combination of laser writing lithography and nanoimprint lithography. Individual pixels matched the industry-standard size (sub 20 _m). The researchers then mapped the greyscale pixel values of the image in the visible domain to the hole diameters of the absorber tuned to the IR 8-14 _m band. Based on the greyscale values of the visible image, the researchers assigned a false IR "color" to each pixel, enabling them to camouflage information from the visible domain to the IR domain. The dipolar coupling between the array of holes/disks and their interaction with the optical cavity dictated the IR response, whereas diffraction into Fabry-Perot cavity modes dominated the visible regime. Thus, the image was viewable only under the specific wavelength in the IR spectral domain. In the visible domain, the image displayed as a single, uniform block of color.

Partnering Opportunity

The research team is looking for partners to develop the technology further for commercialization.

Stage of Development

Prototype available.

Benefit

Market Application