Researchers with the University of Massachusetts at Lowell and MIT have developed a new type of fisheye lens that is flat and crafted from a single piece of glass. The lens is round, according to the researchers, and it is capable of capturing sharp 180-degree panoramas. This is the first flat fisheye lens made from a single piece of glass, which measures 1mm thick.
Ordinary spherical fisheye lenses are made from multiple pieces of glass designed to bend the light in such a way that it produces circular wide-angle images. The newly developed flat lens instead captures wide-angle panoramas by utilizing ‘tiny structures’ that scatter light in place of the curved glass elements in more costly spherical fisheye lenses.
The version of the lense introduced by the researchers is made for infrared photography, but the team says that it could be modified for use as a regular visible spectrum lens, as well. The flat design is ultimately more compact and less expensive to produce than spherical multi-element lenses.
The researchers envision a variety of uses for their lens design beyond interchangeable lenses. The thin, flat nature of the design would make it possible to implement the fisheye into smartphones, for example, eliminating the need to use a third-party lens add-on. Similar implementation could be used with laptops, VR headsets and even devices like medical imaging equipment.
MIT associate professor Juejun Hu, one of the researchers on the project, explained:
This design comes as somewhat of a surprise, because some have thought it would be impossible to make a metalens with an ultra-wide-field view. The fact that this can actually realize fisheye images is completely outside expectation. This isn’t just light-bending — it’s mind-bending.
Metalens refers to a flat lens that has tiny structures for focusing light. While wide-angle metalenses aren’t new, the researchers note that a single piece of glass without any extra optics have been limited to 60-degrees. The newly published study details how the team got around these restrictions to develop an ultra-wide-angle lens capable of capturing 180-degree panoramas without extra components.
This 180-degree fisheye metalens features a single piece of transparent glass made from calcium fluoride with a lead telluride film on one side. A pattern of ‘optical structures’ called meta-atoms was carved into the film using lithographic techniques, the result of which were many ‘nanoscale geometries’ used to bend the light in specific, precise ways.
The carved structures can introduce phase delays into the scattering of the light — depending on their shape — to imitate the natural phase delays produced by the curved glass elements in spherical fisheye lenses. The light passes from the carved structures on the back of the lens through an optical aperture on the front of the lens.
Study co-author Mikhail Shalaginov said:
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. As long as you design the back side properly, you can be sure to achieve high-quality imaging across the entire panoramic view.
The study was partially funded by DARPA through its EXTREME program, which tasks experts with developing optical tools ‘to enable new functionality and/or vastly improve size, weight, and power characteristics of traditional optical systems.’ The agency goes on to explain that EXTREME will ‘explore this optical design space and aims to understand the trade-offs, and harness the possibilities, afforded’ by Engineered Optical Materials (EnMats).