Many things in the natural world are geometrically chiral, meaning they cannot be superimposed onto their mirror image. Being able to observe and analyze the chirality of an object is very important in numerous fields. However, current chiral imaging techniques to resolve polarization and spectral (color) information require multiple cascading components, leading to bulky and expensive pieces of equipment.
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), Cambridge, MA, have developed an ultra-compact, flat lens that can simultaneously capture both spectral information and the chirality of an object.
Chiroptical properties can be probed across the entire visible spectrum using only a single planar lens and a camera, without the addition of other optical components. The lens consists of two arrays of titanium oxide nanofins on one glass substrate, which forms two images of opposite chirality. Blue and green nanofins focus right-circularly polarized light and left-circularly polarized light, respectively, and display the images side-by-side.
To demonstrate the efficacy of the lens, the team imaged the chiral exoskeleton of a beetle. One image was formed by focusing left-circularly polarized light reflected from the beetle and another image was formed from right-circularly polarized light. The left-handed chirality of the beetle’s shell could clearly be seen. The lens can also show when an object is not chiral, such as a coin, which reflects left and right circularly polarized light the same.
A key feature of the lens is its size. The chiral lens is very compact (only 3 mm in diameter and thinner than hair), allowing integration into portable devices.