To capture panoramic views in a single shot, photographers typically use fish-eye lenses — ultra-wide-angle lenses made from multiple pieces of curved glass that distort incoming light to produce wide, bubble-like images. Their spherical, multipiece design makes fisheye lenses inherently bulky and often costly to produce.
Engineers have designed a wide-angle lens that is completely flat and produces crisp, 180-degree panoramic images. The design is a type of “metalens” — a wafer-thin material patterned with microscopic features that work together to manipulate light in a specific way.
In this case, the new fisheye lens consists of a single, flat, millimeter-thin piece of glass covered on one side with tiny structures that precisely scatter incoming light to produce panoramic images, just as a conventional curved, multi-element fisheye lens assembly would. The lens works in the infrared part of the spectrum but it could be modified to capture images using visible light as well.
Metalenses, while still largely at an experimental stage, have the potential to significantly reshape the field of optics. Previously, scientists designed metalenses that produce high-resolution and relatively wide-angle images of up to 60 degrees. To expand the field of view further would traditionally require additional optical components to correct for aberrations or blurriness — a workaround that would add bulk to a metalens design.
Instead, the researchers came up with a simple design that does not require additional components and keeps a minimum element count. The new metalens is a single transparent piece made from calcium fluoride with a thin film of lead telluride deposited on one side. The team then used lithographic techniques to carve a pattern of optical structures into the film.
Each structure, or “meta-atom,” is shaped into one of several nanoscale geometries, such as a rectangular or a bone-shaped configuration, that refracts light in a specific way; for example, light may take longer to scatter or propagate off one shape versus another — a phenomenon known as phase delay.
In conventional fisheye lenses, the curvature of the glass naturally creates a distribution of phase delays that ultimately produces a panoramic image. The team determined the corresponding pattern of meta-atoms and carved this pattern into the back side of the flat glass. On the front side, the team placed an optical aperture, or opening, for light. When light comes in through this aperture, it will refract at the first surface of the glass and then will get angularly dispersed. The light will then hit different parts of the backside from different and yet continuous angles.
The new lens can be adapted to other wavelengths of light. To make a similar flat fisheye lens for visible light, for instance, the optical features will have to be made smaller to better refract the particular range of wavelengths. The lens material would also have to change but the general architecture would remain the same.
The new design could potentially be adapted for a range of applications, with thin, ultra-wide-angle lenses built directly into smartphones and laptops rather than physically attached as bulky add-ons. The low-profile lenses might also be integrated into medical imaging devices such as endoscopes as well as in virtual reality glasses, wearable electronics, and other computer vision devices.