The Harvard School of Engineering and Applied Sciences (SEAS) has presented a new type of lenses that can completely revolutionize the market, and that can have important repercussions on the development of virtual reality headsets.
This is a huge leap compared to a prototype shown in 2012. The new lenses are ultra-thin and completely flat, made of a glass substrate and tiny silicon antennas that concentrate light. The light that passes through this lens curves instantly instead of gradually as with traditional lenses. Such a curvature can be designed by an algorithm and adjusted to perform almost any purpose.
“This means that more complicated effects such as color correction, which in a conventional optical system requires light to pass through several thick lenses one after the other, can be achieved in an extremely thin and miniaturized device,” says research director Federico Capasso.
Bernard Kress, the top optics expert in the Google X department, values this advance very positively:
“Google [X], and especially the Google Glass group, relies entirely on state-of-the-art optical technologies to develop products that offer greater functionality, can be easily mass-produced, take up little space and are lightweight, without compromising their efficiency. Last year, we proposed to Professor Capasso’s group the achievement of a goal that was unattainable using flat lenses. Although there are various ways to design achromatic lenses, until now there was no solution to implement a flat, dispersion-free optical element that simultaneously offers uniform efficiency and the same diffraction angle for three different wavelengths. We were very pleased that Professor Capasso accepted our challenge, and we were also surprised to see that they were able to solve the problem in just one year.”
The new lenses, dubbed “achromatic metasurface”, dramatically improve the prototype shown by Capasso’s research group in 2012. That prototype, the first in its category, corrected some of the aberrations of conventional lenses, but suffered from the limitation of focusing light of a single wavelength, and its efficiency was low. The new model uses a dielectric material instead of metallic for the nanoantennas, a change that greatly improves efficiency and, combined with a new design approach, allows their operation with a wide range of wavelengths. And most importantly, the new design allows the creation of two different planar optical devices. The first, instead of sending different colors in different directions like a conventional grid, deflects three wavelengths at exactly the same angle. In the second, the three lengths converge at the same point. Therefore, a flat lens can create a color image by focusing on the primary colors, red, green and blue. Computer simulations suggest that, using a similar architecture, lenses capable of collimating many different wavelengths, and not just three, could be created.
“This is a giant step forward when it comes to manufacturing a planar optical technology in a very small size that overcomes the limitations of standard planar lenses, known as diffractive,” says Capasso. “It also opens new doors to new functionalities due to the amount of space that is gained thanks to metasurfaces.”
The truth is that our mouths water when we think about the possibilities. Without being experts in optics, who knows if this would allow the use of a curved screen in an HMD that completely covers our viewing angle and leave behind the barrier of just 100º FOV that can be achieved with the limitations of current lenses. Undoubtedly, this discovery has the potential to be a real revolution, and we hope that other HMDs developers will make some evaluation of it as soon as possible. For now, it seems that in Google Glass they are delighted.
