An optic to replace space and its application towards ultra-thin imaging systems

Nature Communications volume  12, Article number: 3512 (2021 ) Cite this article

Centuries of effort to improve imaging has focused on perfecting and combining lenses to obtain better optical performance and new functionalities. The arrival of nanotechnology has brought to this effort engineered surfaces called metalenses, which promise to make imaging devices more compact. However, unaddressed by this promise is the space between the lenses, which is crucial for image formation but takes up by far the most room in imaging systems. Here, we address this issue by presenting the concept of and experimentally demonstrating an optical ‘spaceplate’, an optic that effectively propagates light for a distance that can be considerably longer than the plate thickness. Such an optic would shrink future imaging systems, opening the possibility for ultra-thin monolithic cameras. More broadly, a spaceplate can be applied to miniaturize important devices that implicitly manipulate the spatial profile of light, for example, solar concentrators, collimators for light sources, integrated optical components, and spectrometers.

Metasurfaces—engineered surfaces consisting of sub-wavelength scatterers—have attracted a great deal of attention for enabling flat optical components1,2,3,4,5,6. These devices have been implemented in a diverse set of novel linear7,8,9,10,11 and nonlinear optical12,13,14 applications, including sub-wavelength-scale broadband achromatic lenses15, the generation of various transverse spatial modes1,8, lasing16,17, polarimetry18, and holograms19, among others. Notably, metalenses are seen as the most promising by far due to their impact in miniaturizing imaging systems20,21. However, in all imaging systems, lenses represent just one of the two main components; the other, sometimes overlooked in this context, is the millimeter-to-meter-scale optical propagation surrounding the lenses and separating them from the object and image. As evidenced by the long physical length of a typical (e.g., Galilean) telescope, the distances between lenses are just as critical to image formation as the lenses themselves, and can easily be greater than the summed thicknesses of the lenses by an order of magnitude. To date, no work has been published that addresses this dominant contribution to the size of many optical systems.

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