| Apr 14, 2022 |
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(Nanowerk News) Researchers have designed a new compact camera that acquires wide-angle images of high-quality using an array of metalenses — flat nanopatterned surfaces used to manipulate light. By eliminating the bulky and heavy lenses typically required for this type of imaging, the new approach could enable wide-angle cameras to be incorporated into smartphones and portable imaging devices for vehicles such as cars or drones.
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Tao Li and colleagues from Nanjing University in China report their new ultrathin camera in Optica (“Planar wide-angle-imaging camera enabled by metalens array”). The new camera, which is just 0.3 centimeters thick, can produce clear images of a scene with a viewing angle of more than 120 degrees.
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| Researchers designed a new compact camera that acquires high-quality wide-angle images using an array of metalenses. Their new planar camera (MIWC) produced clearer images of pictures projected across a curved screen compared to a camera based on a single traditional metalens. (Image: Tao Li, Nanjing University)
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Wide-angle imaging is useful for capturing large amounts of information that can create stunning, high-quality images. For machine vision applications such as autonomous driving and drone-based surveillance, wide-angle imaging can enhance performance and safety, for example by revealing an obstacle you couldn’t otherwise see while backing up in a vehicle.
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“To create an extremely compact wide-angle camera, we used an array of metalenses that each capture certain parts of the wide-angle scene,” said Li. “The images are then stitched together to create a wide-angle image without any degradation in image quality.”
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Miniaturizing the wide-angle lens
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Wide-angle imaging is usually accomplished with a fish-eye compound lens or other type of multilayer lens. Although researchers have previously tried to use metalenses to create wide-angle cameras, they tend to suffer from poor image quality or other drawbacks.
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In the new work, the researchers used an array of metalenses that are each carefully designed to focus a different range of illumination angles. This allows each lens to clearly image part of a wide-angle object or scene. The clearest parts of each image can then be computationally stitched together to create the final image.
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“Thanks to the flexible design of the metasurfaces, the focusing and imaging performance of each lens can be optimized independently,” said Li. “This gives rise to a high quality final wide-angle image after a stitching process. What’s more, the array can be manufactured using just one layer of material, which helps keep cost down.”
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Seeing more with flat lenses
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To demonstrate the new approach, the researchers used nanofabrication to create a metalens array and mounted it directly to a CMOS sensor, creating a planar camera that measured about 1 cm × 1 cm × 0.3 cm. They then used this camera to image a wide-angle scene created by using two projectors to illuminate a curved screen surrounding the camera at a distance of 15 cm.
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| The researchers fabricated a metalens array (enlarged on the right) and mounted it directly to a CMOS sensor. This created a planar camera that measured about 1 cm × 1 cm × 0.3 cm. (Image: Tao Li, Nanjing University)
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They compared their new planar camera with one based on a single traditional metalens while imaging the words “Nanjing University” projected across the curved screen. The planar camera produced an image that showed every letter clearly and had a viewing angle larger than 120°, more than three times larger than that of the camera based on a traditional metalens.
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The researchers note that the planar camera demonstrated in this research used individual metalenses just 0.3 millimeters in diameter. They plan to enlarge these to about 1 to 5 millimeters to increase the camera’s imaging quality. After optimization, the array could be mass produced to reduce the cost of each device.
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