Harvard Engineers have created a ground-breaking lens. This new single ‘metalens’ can focus all colours of the rainbow in one point opening up new possibilities for virtual and augmented reality technology.
The team of researchers from Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have called the new technology a ‘metalens’; in a world first, this single lens is able to focus the visible spectrum of light (including white light) onto the same spot in high resolution
It works by using an array of titanium dioxide nanofins. This allows the material to equally focus wavelengths and eliminate chromatic aberration (the effect produced when different wavelengths of light refract through slightly different angles, resulting in a failure to focus).
What are Metalenses
The team have defined their metalens as ‘flat surfaces that use nanostructures to focus light’.
Applications for Metalenses
The team believes that Metalenses could completely revolutionise optics by replacing traditional bulky and curved lenses with a flat surface.
Up to now, metalenses have remained limited in the spectrum of light they can focus well. This has limited their use in applications that would require a full range of light like Augmented Reality and Virtual Reality.
The teams’ new single lens can not only focus the entire visible spectrum of light but do so in high resolution. Something previously only achieved using multiple lenses.
Chromatic Aberrations – Why has focusing the visible spectrum is so challenging
Focusing the all the colours of the spectrum has been a challenge up to now because wavelengths of light move through materials at different speeds.
For example – red wavelengths move through glass faster than blue. This means each colour reaches the same location on an image sensor at different times so the image does not correctly focus. The resulting distortions are called chromatic aberrations.
One of the most significant challenges in designing an achromatic broadband lens is making sure that the outgoing wavelengths from all the different points of the metalens arrive at the focal point at the same time … by combining two nanofins into one element, we can tune the speed of light in the nanostructured material, to ensure that all wavelengths in the visible are focused in the same spot, using a single metalens. This dramatically reduces thickness and design complexity compared to composite standard achromatic lenses Wei Ting Chen, a postdoctoral fellow at SEAS and first author of the paper
Up to now, cameras and optical instruments engineers have been forced to use multiple curved lenses to correct these aberrations,.
The use of multiple lenses – each of which will often have different thicknesses and are frequently made from different materials – adds to the weight and bulk of a modern lens.
What next
The goal of the team now is to scale up the lens (which is only around 1cm in diameter). A larger lens will allow for a new host of new possible applications in virtual and augmented reality.
The research is published in Nature Nanotechnology.
Published by Wei Ting Chen, Alexander Y. Zhu, Vyshakh Sanjeev, Mohammadreza Khorasaninejad, Zhujun Shi, Eric Lee, Federico Capasso as A broadband achromatic metalens for focusing and imaging in the visible. Nature Nanotechnology, 2018; DOI: 10.1038/s41565-017-0034-6<
