Abstract
Optical elements play a crucial role in many modern systems, from cellphones to missiles. The miniaturization trend poses a challenge to optics, since classical lenses and mirrors tend to be bulky. One way of dealing with this challenge is using flat optics. For many years flat optics has been implemented using diffractive optics technology, but in the last two decades a new technology called metasurfaces has emerged. This technology does not replace diffractive optics, but rather expands on it, leveraging the new ability to manufacture subwavelength features on optical substrates. For imaging and focusing applications, diffractive lenses and metalenses are used, as a subset of diffractive optics and metasurfaces, respectively. Recently there has been debate over whether metalenses offer any real advantages over diffractive lenses. In this commentary we will try to gain some insight into this debate and present our opinion on the subject.
Highlights
Optical elements play a crucial role in many modern systems, from cellphones to missiles
In a metalens, which is a type of metasurface, the phase is induced via the response of nanostructures built on the surface of the substrate material (Fig. 1c). This contrasts with a conventional diffractive lens (CDL) where the phase inducing mechanism is still like that of a refractive lens—based on the length of the ray path inside the lens material
For a lens to be considered a metalens it must have a subwavelength quasiperiodic structure, as opposed to a CDL which is based on a super-wavelength quasi-periodic structure
Summary
1234567890():,; Optical elements play a crucial role in many modern systems, from cellphones to missiles. One way of dealing with this challenge is using flat optics. For many years flat optics has been implemented using diffractive optics technology, but in the last two decades a new technology called metasurfaces has emerged. This technology does not replace diffractive optics, but rather expands on it, leveraging the new ability to manufacture subwavelength features on optical substrates. There has been debate over whether metalenses offer any real advantages over diffractive lenses. In this commentary we will try to gain some insight into this debate and present our opinion on the subject
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