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SPIE O+P 2018: bright future for 'game-changing' lens concept

20 Aug 2018

Components featuring titanium oxide nanofins set to appear in consumer electronics and medicine, predicts San Diego plenary speaker Federico Capasso.

by Ford Burkhart in San Diego
“It’s revolutionary,” says Federico Capasso, an advocate of the trailblazing metasurface approach to lens-making that could, he said, result in replacing existing lenses in microscopes, cameras, laptops, and cell phones.

The Harvard professor and metamaterials expert, an opening day plenary speaker at SPIE’s Optics+Photonics symposium, believes that such structures, featuring a surface comprising titanium dioxide nanofins just a few microns in size, will be at the heart of the future of lenses, and emphasized their value for biomedical imaging.

At a sobering moment during his talk, Capasso recalled a time when a Harvard colleague was investigating lung cancer, and needed to see details of the developing tumor at the microscopic scale.

Capasso said his students designed a high-resolution lens - a metalens - for her bronchoscope to look at the diseased tissue. In turn, she was able to locate the cancer and for the first time to see images that could not be captured by standard commercial lenses.

“Metalenses are thin, easy to fabricate and cost-effective, across the whole visible range of light,” he said. “This is the next big step.”

Aberration control
Capasso, who is the Robert L. Wallace Professor of Applied Physics at Harvard, gave his talk during the opening plenary session at the San Diego Convention Center, under the title “Metasurface Flat Optics: Unifying Semiconductor Manufacturing and Lens Making.”

One key advantage of the metalens approach revolves around chromatic aberration, an effect that results from the way that different wavelengths move through both conventional optics and tissue at different speeds. Different colors reach the same location at different times, with different foci, creating distortions.

Capasso’s single, flat metalens can focus the entire visible spectrum of light in the same spot, in high resolution.

To explain, he showed slides featuring several patterns of rows of the tiny fins that are able to eliminate chromatic aberration. The effect is achieved by optimizing the shape, width, distance, and height of the nanofins, which control the speed of different wavelengths of light simultaneously.

With traditional optics, multiple lenses must be used to achieve that, meaning that correcting for distortion may call for as many as six or seven optical components.

Instead, paired nanofins control the refractive index on the metasurface and are tuned to yield different time delays for the light passing through different fins.

Product launch next year?
Capasso said his laboratory will use tools developed for semiconductor production to create new kinds of flat or planar optics. “Metal surfaces give you control of the plane, amplitude and polarization of light,” he said. This can reduce the complexity of existing lenses, while increasing their multi-functionality."

Fabrication using a single mask should ensure low-cost production, with the lightweight components also suitable for vertical integration. “You can design anything you want in terms of dispersion control,” said the Harvard researcher. “The textbooks tell you that this is not possible, but it is.”

What’s more, Capasso’s own laboratory has spun out a company to commercialize these lenses and expects to launch a product as early as 2019. “There is a real future here to change, at a fundamental level, this kind of refractive optics,” he said. “This should be game changing.”

The startup, called Metalenz, was co-founded last year by Capasso, alongside Harvard researcher Rob Devlin and businessman Bart Riley, the firm’s CEO.

About the Author

Ford Burkhart is a writer based in Tucson, Arizona.

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