World’s Thinnest Lens to Revolutionize Cameras

Ultra thin lenses on the screen. (Source: Stuart Hay, ANU)

Ultra thin lenses on the screen. (Source: S. Hay, ANU)

Scientists have created the world’s thinnest lens, one two-thousandth the thickness of a human hair, opening the door to flexible computer displays and a revolution in miniature cameras. Lead researcher Yuerui Lu from Australian National Univer­sity ANU Research School of Engi­neering said the discovery hinged on the remarkable potential of the molyb­denum disulphide crystal.

“This type of material is the perfect candidate for future flexible displays,” said Lu, leader of Nano-Electro-Mechanical System (NEMS) Laboratory in the ANU Research School of Engineering. “We will also be able to use arrays of micro lenses to mimic the compound eyes of insects.”

The 6.3-nanometre lens outshines previous ultra-thin flat lenses, made from 50-nanometre thick gold nano-bar arrays, known as a metamaterial. “Molybdenum disulphide is an amazing crystal,” said Lu. “It survives at high temperatures, is a lubricant, a good semi­conductor and can emit photons too. The capability of mani­pulating the flow of light in atomic scale opens an exciting avenue towards unpre­cedented minia­turisation of optical components and the inte­gration of advanced optical functiona­lities.”

Molybdenum disulphide is in a class of materials known as chalcogenide glasses that have flexible electronic charac­teristics that have made them popular for high-technology components. Lu’s team created their lens from a crystal 6.3-nanometres thick – 9 atomic layers – which they had peeled off a larger piece of molybdenum disulphide with sticky tape. They then created a 10-micron radius lens, using a focussed ion beam to shave off the layers atom by atom, until they had the dome shape of the lens.

The team discovered that single layers of molybdenum disulphide, 0.7 nanometres thick, had remarkable optical properties, appearing to a light beam to be 50 times thicker, at 38 nanometres. This property, known as optical path length, determines the phase of the light and governs interference and dif­fraction of light as it propagates. “At the beginning we couldn’t imagine why molybdenum disulphide had such surprising pro­perties,” said Lu.

Colla­borator Assistant Professor Zongfu Yu at the Univer­sity of Wisconsin, Madison, developed a simulation and showed that light was bouncing back and forth many times inside the high refrac­tive index crystal layers before passing through. Molyb­denum disulphide crystal’s refrac­tive index, the property that quan­tifies the strength of a material’s effect on light, has a high value of 5.5. For comparison, diamond, whose high refrac­tive index causes its sparkle, is only 2.4, and water’s refrac­tive index is 1.3. (Source: ANU)

Reference: J. Yang et al.: Atomically thin optical lenses and gratings, Light: Sci. & App. (2016) 5, e16046, DOI: 10.1038/lsa.2016.46, online 11 March 2016

Link: Research School of Engineering, College of Engineering and Computer Science, the Australian National University, Canberra, Australia

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