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An engineering research team from the University of Utah (United States) has recently developed a new generation of camera lenses that are almost completely flat. This advanced imaging technology could have applications as diverse as flattening smartphone design without reducing functionality, enabling camera-carrying drones to drastically increase their range with reduced weight, conducting imaging experiments in extremely narrow spaces, and military uses.
The research, published in Proceedings of the National Academy of Sciences (PNAS) in 2019, demonstrates the possibility for broadband long-wave infrared (LWIR) imaging in a single flat lens no thicker than 10 μm (or 0.01 mm, about half the width of the smallest human hairs).
Not only are these lenses considerably thinner than even the thinnest camera lenses in commercial use today (the latest smartphone lenses measure up to 3 mm thick and are the main barrier to ultra-flat smartphone design), but the lenses are around 100 times lighter than comparable reflective lenses.
How Do You Flatten a Lens?
It is well known that lenses – be they for imaging, telescopic or microscopic uses – work due to curvature in the lens material which magnifies light, however, new technology has allowed a lens to be flat and bend light to capture an image.
The researchers designed a lens made of countless minute components. These nano-optic components are positioned so that they can diffract light around the lens until it reaches the sensor, removing the need for curvature in a single lens component that is necessarily thick.
These so-called multilevel diffractive lenses (MDLs) are much easier to manufacture than previous iterations in ultra-thin camera lens technology such as metalenses, which are made of discrete constituent parts. In contrast, MDLs are formed from a patterned polymer and can be manufactured at a greatly reduced cost and difficulty.
New Polymers, Processes and Algorithms
To create these ultra-thin MDLs, the team had to engineer a new polymerization technique, design new manufacturing processes, and create new algorithms to position the microstructure parts of the lens effectively.
They designed two MDLs with slightly different approaches. Firstly using advanced lithography techniques to “print” the MDL structure onto a polymer base, then secondly, using nanotechnology methods to polymerize silicon (Si). The former approach resulted in lenses that are slightly less powerful, although it could be much cheaper and simpler to manufacture at scale than the Si method.
The designs were obtained using a gradient-descent based search algorithm that the team modified to maximize focusing efficiency.
Applications for Ultra-Thin Camera Lenses
The applications for this technology are as wide as the lenses are thin. While the two lens designs that the researchers developed and tested only captured light in the infrared (IR) range, they attest that their results “will have important applications for all spectral bands”.
If the new methods developed by the team for creating ultra-thin lenses can be successfully applied to a wider range of lenses, then application areas can include defense, medicine, agriculture and even environmental monitoring.
Specific applications for ultra-thin, lightweight lenses might be in camera-carrying drones. Typically these are restricted in range due to the prohibitive weight of the imaging equipment they carry. The ultra-lightweight MDL demonstrated in this research would enable drones to travel much further than otherwise possible with the same amount of electrical charge. This would have significant ramifications in the field of environmental monitoring, as more and more remote locations could be imaged giving valuable and otherwise unattainable data to environmental scientists.
In medicine, these tiny lenses could operate inside the human body in places that conventional curved lenses cannot reach. This would give medical practitioners valuable information about patients’ bodies, as well as helping to develop our understanding of the human body in general.
In terms of the consumer market, such ultra-thin and lightweight lenses could help unlock a new generation of flat smartphones. Combined with material advances such as graphene, smartphones of the future could become almost entirely flat. Similar to this, applications in wearable technology and biotechnology could become possible, bringing about a futuristic world of augmented realities and live image sensing and analysis, supported by these flat lenses.
References and Further Reading
Meem, M., Banerji, S., Majumder, A., Vasquez, F.G., Sensale-Rodriguez, B. and Menon, R. (2019). Broadband lightweight flat lenses for long-wave infrared imaging. Proceedings of the National Academy of Sciences, 116(43), pp.21375–21378. https://doi.org/10.1073/pnas.1908447116