Engineers working to miniaturize optical systems for modern electronics have seen great success with the lens and optical sensors. It has been more difficult to reduce the size of the third component of an optical system.
A thin, transparent device called a spaceplate is being developed to replace some or all of the free space. For the first time, Cornell researchers have defined the limits of spaceplates in a paper published in the journal Optica. Limits of spaceplates.
In the quest to miniaturize optical systems, an important aspect is the large free-space volume between the detector and the lens.
Before digital cameras, the length of the free space behind a lens was more important than it is now. Light waves coming from different directions are able to converge at the sensor because of the free space. It's one of the reasons why long camera lens designed to focus on and amplify a distant subject are so popular. The optical phase response of free space is mimicked by spaceplates.
In the past, Monticone and Aobo Chen had used computer simulations to demonstrate how they would work in optical systems. The limits of a spaceplate's ability to maximize three fundamental optical parameters are being defined by this work.
"Meeting these three goals at the same time is very difficult," Monticone said. The paper tries to clarify the general physical mechanism behind the space compression effect.
Prior research into spaceplate technology yielded impractical and inefficient designs that needed to be immersed in a material with a highRefractive index, such as oil. The devices couldn't be used to miniaturize optical systems.
Nobody was sure if spaceplates would work for the entire visible spectrum of light and in free space. We wanted to see if there were any physical limits that would prevent spaceplates from working for real cameras.
The boundaries of the paper will tell other engineers how far away they are from the global fundamental limits of the spaceplate devices they are designing. "That's, I think, very useful," he said. We wrote this paper because of that.
Spaceplates can be designed using the same materials that conventional systems are made from, whether it's layers of glass and other transparent materials or a patterned surface. You don't want the space plate to absorb light if it's highly transmissive.
Monticone said that a spaceplate could be made out of a stack of layers and have at least two different Refractive index. The thickness and spacing can be improved.
Spaceplate technology can be used in many other ways. Spaceplates can be used to make use of a wider range of the spectrum. While using computer models, Monticone and Shastri want to design physical experiments with spaceplates.
The next step will be the demonstration of a spaceplate working in free space. Computational design methods will help us maximize spaceplates to work as close to our limits as possible. We might be able to combine a flat lens and a spaceplate within a single device, realizing ultra-thin, monolithic, planar optical systems for a variety of applications.
More information: Kunal Shastri et al, To what extent can space be compressed? Bandwidth limits of spaceplates, Optica (2022). DOI: 10.1364/OPTICA.455680 Journal information: Optica
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