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A new patent file reveals innovative research by the US Army in the field of anti-reflective coating, inspired by nature. In addition to improving the optical components used by soldiers, this tech could be used to increase the efficiency of solar panels, cut glare on flat-panel TVs, outdoor signage, etc.
Moths are nocturnal and have evolved eyes with a periodic, surface-graded structure so that light bends instead of reflecting. “The surface of the eye of a moth is covered by bumps that are each roughly 200 nm high and whose centers are spaced approximately 300 nm apart. Since the bumps are smaller than the wavelength of visible light, visible light sees the surface as… (in a way that) decreases reflection by effectively removing the air-lens interface. Thus, the bumps serve as an anti-reflective coating on the eye of the moth,” according to the Army’s patent application.
Vincent Schnee from the U.S. Army’s Night Vision and Electronic Sensors Directorate is the only inventor named in the patent filing. Instead of laser etching individual optical elements, which takes days and days, Schnee is thinking like a press operator at a newspaper.
The document explains that the first step is to cover a silicon cylinder in the moth-eye pattern using two-photon lithography, a micro-3D printing technique using a tightly focused laser beam. The etched cylinder is then used as a rolling stamp, pressing the moth-eye pattern on the optical lens using epoxy with germanium nanoparticles as its ink.
In addition to scaling production, the material used to create the moth-eyed nano-layer can be the same material as the optical element.
“This allows perfect matching of indices of refraction between the optical element and the anti-reflective coating,” according to Schnee’s patent application cited by techlinkcenter.org. “Such a perfect match is not easily achieved with conventional layered dielectric anti-reflective coatings.”