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An optical component known as a 鈥渟paceplate鈥� could squeeze an entire camera and long-focus lens into a wafer-thin chip, paving the way for even greater miniaturisation of smartphones and other devices. Limitations have held spaceplates back, but now theoretical work shows that they aren鈥檛 just pie in the sky.

The lenses and sensors used in cameras have shrunk radically over the years, but the remaining hurdle to further miniaturisation is the empty space needed between the two. After light passes through a lens, it must travel some distance to reach the focal point, which is where sensors are located 鈥� this is why many modern smartphones have a 鈥渃amera bump鈥� on the back, to give the light enough room for the camera to focus.

Spaceplates offer a way round this by using substances called metamaterials to do away with the need for space. 鈥淎 spaceplate mimics the way light propagates and spreads in empty space, but over a smaller distance,鈥� says at Cornell University in Ithaca, New York. 鈥淲ith a spaceplate, light effectively 鈥榚xperiences鈥� more space than is actually there.鈥�

The idea was and introduced two possible types of spaceplate: one was made up of 25 alternating layers of silica and silicon, the other was comprised of a homogenous section made of calcite that needed to be immersed in glycerol or linseed oil in order to properly focus light.

But early spaceplate prototypes only worked in one colour or required immersion in oil, so they haven鈥檛 got off the ground and have left some people doubting that they would ever work as desired.

Now, Monticone and his colleagues have shown, mathematically and with simulations, that physics does provide a way to build a spaceplate that drastically reduces the length needed to achieve focusing while maintaining high image quality and working across the visible spectrum of light. They don鈥檛 know how exactly it would need to be designed to work, but they have proved that it is theoretically possible.

, a member of the team and an author of the original 2021 paper while at the University of Ottawa in Canada, says the idea behind layered spaceplates is that they work on a similar principle to anti-reflective coatings on glasses, where a thin layer on top of the lens creates a second, out-of-phase reflection that cancels out the reflection from the lens itself. Light travelling through a spaceplate is reflected numerous times between layers.

鈥淭hey鈥檙e not bending the light, what they鈥檙e doing is they鈥檙e bouncing it back and forth,鈥� says Reshef. The light is bounced all the way to a focal point that would otherwise require more thickness.

Reshef, who now works at an optics start-up, says that although the physics behind spaceplates is maturing, the initial spaceplate design was created by a genetic algorithm that tried a vast array of potential solutions and slowly converged on a working design, because nobody was sure where to start. Whether this design is the best way to make a spaceplate remains unknown.

鈥淲e鈥檝e answered the most frequently asked question about spaceplates 鈥� and arguably the most important roadblock for the adoption of this platform 鈥� namely, whether spaceplates can work over a broad range of colours,鈥� says Monticone. The next step will be the experimental demonstration of a high-quality optical spaceplate and its integration in an optical system like a smartphone camera.