Extreme-depth-of-focus imaging with a flat lens

Abstract

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 ∼ 6 m in our experiments. Specifically, when illuminated by collimated light at λ = 0.85 µ m , 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.

Low cost and long-focal-depth metallic axicon for terahertz frequencies based on parallel-plate-waveguides

“…These results demonstrate the capability of this structure to effectively focus the THz radiation in a similar fashion to conventional lenses. In addition, the focusing efficiency is calculated by the ratio of the power inside a 3×FWHM region to the power inside the lens area 28 . The result of this calculation is shown in Fig.…”

Experimental Demonstration of Genetic Algorithm Based Metalens Design for Generating Side‐Lobe‐Suppressed, Large Depth‐of‐Focus Light Sheet

“…Besides, a quite astonishing result revealed in recently published article demonstrated that, an inverse designed 1.8 mmlarge multi-level diffractive lens can achieve diffraction-limit extreme long DOF (≈1200 mm). [55] Obviously, it holds promising potential in applications such as optical imaging with an ultralarge field of view (as demonstrated in the article), in optical lithography, etc. However, it seems not so attractive when applied to LSFM because of the following weaknesses: First, the 3D optical patterns with the non-negligible side lobes (as revealed in Figure S5a-d Second, it may meet with the similar problems encountered by the prism, SQUBIC lens, shifted axicon, and log-aspherical lens when lowered to 1D structure (assume that the inverse designed phase profile is axially symmetric).…”

Intelligent designs in nanophotonics: from optimization towards inverse creation

“…The high numerical aperture (NA with a value of 1.48) meta-lens (oil immersion) exhibited a 207 nm full width at half maximum (FWHM) of a beam spot with an operational efficiency of 48%, representing one of highest NA of any metalens by that time. Other types of traditional algorithms such as GA and binary search techniques are also demonstrated in, e.g., Pancharatnam-Berry type metalens [76] as well as multi-level diffractive lenses [77][78][79], respectively.…”