Wide field-of-view imaging with a metalens

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A research group from Nanjing University has published a new paper titled "Planar wide-angle-imaging camera enabled by metalens array" in the recent issue of Optica.

Abstract:
Wide-angle imaging is an important function in photography and projection, but it also places high demands on the design of the imaging components of a camera. To eliminate the coma caused by the focusing of large-angle incident light, traditional wide-angle camera lenses are composed of complex optical components. Here, we propose a planar camera for wide-angle imaging with a silicon nitride metalens array mounted on a CMOS image sensor. By carefully designing proper phase profiles for metalenses with intentionally introduced shifted phase terms, the whole lens array is capable of capturing a scene with a large viewing angle and negligible distortion or aberrations. After a stitching process, we obtained a large viewing angle image with a range of >120 degrees using a compact planar camera. Our device demonstrates the advantages of metalenses in flexible phase design and compact integration, and the prospects for future imaging technology.


Metalens array mounted directly on a CMOS camera




Schematic diagram of the principle and device architecture. (a) Schematics of wide-angle imaging by MIWC. Zoom-in figure shows the imaging principle with each part of the wide-angle image clearly imaged separately by each metalens. (b) Photograph of MIWC. The metalens array can be seen in the middle of the enlarged figure on the right. (c) Architecture of MIWC. The metalens array is integrated directly on the CMOS image sensor (DMM 27UJ003-ML) and fixed by an optically clear adhesive (OCA) tape (Tesa, 69402).



Experimental wide-angle imaging results by MIWC. (a) Projected “NANJING UNIVERSITY” on the curved screen covers a viewing angle of 120° and then is imaged by MIWC. (b) Imaging results and corresponding mask functions of lenses with designed angles of −57.5∘, 0°, 57.5°. (d) Imaging result of a traditional metalens showing limited field of view. (e) Final imaging result of MIWC by processing with mask functions and sub-images, which shows three times larger FOV compared with the traditional lens.

Press release: https://phys.org/news/2022-04-miniature-wide-angle-camera-flat-metalenses.html

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Lensless camera for in vivo microscopy

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A team comprised of researchers from Rice University and Baylor College of Medicine in Houston, TX has published a Nature Biomedical Engineering article titled "In vivo lensless microscopy via a phase mask generating diffraction patterns with high-contrast contours."

Abstract: The simple and compact optics of lensless microscopes and the associated computational algorithms allow for large fields of view and the refocusing of the captured images. However, existing lensless techniques cannot accurately reconstruct the typical low-contrast images of optically dense biological tissue. Here we show that lensless imaging of tissue in vivo can be achieved via an optical phase mask designed to create a point spread function consisting of high-contrast contours with a broad spectrum of spatial frequencies. We built a prototype lensless microscope incorporating the ‘contour’ phase mask and used it to image calcium dynamics in the cortex of live mice (over a field of view of about 16 mm2) and in freely moving Hydra vulgaris, as well as microvasculature in the oral mucosa of volunteers. The low cost, small form factor and computational refocusing capability of in vivo lensless microscopy may open it up to clinical uses, especially for imaging difficult-to-reach areas of the body.

 


 


 


 

Link to full article (open access): https://www.nature.com/articles/s41551-022-00851-z

Press release: https://www.photonics.com/Articles/Lensless_Camera_Captures_Cellular-Level_3D_Details/a67869

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Lensless Imaging with Fresnel Zone Plates

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Although the idea of Fresnel zone plates is not new and can be traced back several decades to X-ray imaging and perhaps to Fresnel's original paper from 1818*, there is renewed interest in this idea for visible light imaging due to the need for compact form-factor cameras.

This 2020 article in the journal Light: Science and Applications by a team from Tsinghua University and MIT describes a lensless image sensor with a compressed-sensing style inverse reconstruction algorithm for high resolution color imaging.

Lensless imaging eliminates the need for geometric isomorphism between a scene and an image while allowing the construction of compact, lightweight imaging systems. However, a challenging inverse problem remains due to the low reconstructed signal-to-noise ratio. Current implementations require multiple masks or multiple shots to denoise the reconstruction. We propose single-shot lensless imaging with a Fresnel zone aperture and incoherent illumination. By using the Fresnel zone aperture to encode the incoherent rays in wavefront-like form, the captured pattern has the same form as the inline hologram. Since conventional backpropagation reconstruction is troubled by the twin-image problem, we show that the compressive sensing algorithm is effective in removing this twin-image artifact due to the sparsity in natural scenes. The reconstruction with a significantly improved signal-to-noise ratio from a single-shot image promotes a camera architecture that is flat and reliable in its structure and free of the need for strict calibration.








Full article is available here: https://www.nature.com/articles/s41377-020-0289-9

* "Calcul de l'intensité de la lumière au centre de l'ombre d'un ecran et d'une ouverture circulaires eclairés par un point radieux," in Œuvres Complètes d'Augustin Fresnel 1866-1870. https://gallica.bnf.fr/ark:/12148/bpt6k1512245j/f917.item

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