Thursday, March 12, 2020

EDoF is Back? reports that OSA paper "Extreme-depth-of-focus imaging with a flat lens" by Sourangsu Banerji, Monjurul Meem, Apratim Majumder, Berardi Sensale-Rodriguez, and Rajesh Menon from University of Utah, Salt Lake City, proposes a flat lens with extended depth of focus:

"The new lens eliminates the need for focusing and allows any camera to keep all the objects in focus simultaneously," said research team leader Rajesh Menon. "Conventional cameras also use multiple lenses to keep different colors of light in focus simultaneously. Since our design is very general, we can also use it to create a single flat lens that focuses all colors of light, drastically simplifying cameras even further."

"Our flat lenses can drastically reduce the weight, complexity and cost of cameras and other imaging systems, while increasing their functionality," said Menon. "Such optics could enable thinner smartphone cameras, improved and smaller cameras for biomedical imaging such as endoscopy, and more compact cameras for automobiles."

"A lens performs an approximately one-to-one mapping from the object to the image plane. This mapping in the image plane is maintained within a depth of field (or referred to as depth of focus, if the object is at infinity). This necessitates refocusing of the lens when the images are separated by distances larger than the depth of field. Such refocusing mechanisms can increase the cost, complexity, and weight of imaging systems. Here we show that by judicious design of a multi-level diffractive lens (MDL) it is possible to drastically enhance the depth of focus by over 4 orders of magnitude. Using such a lens, we are able to maintain focus for objects that are separated by as large a distance as ∼6m in our experiments. Specifically, when illuminated by collimated light at 𝜆=0.85µm, the MDL produced a beam, which remained in focus from 5 to 1200 mm. The measured full width at half-maximum of the focused beam varied from 6.6 µm (5 mm away from the MDL) to 524 µm (1200 mm away from the MDL). Since the side lobes were well suppressed and the main lobe was close to the diffraction limit, imaging with a horizontal × vertical field of view of 40∘×30∘ over the entire focal range was possible. This demonstration opens up a new direction for lens design, where by treating the phase in the focal plane as a free parameter, extreme-depth-of-focus imaging becomes possible."

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