Recent Progress on Ultrathin Metalenses for Flat Optics

Abstract

As technology advances, electrical devices such as smartphones have become more and more compact, leading to a demand for the continuous miniaturization of optical components. Metalenses, ultrathin flat optical elements composed of metasurfaces consisting of arrays of subwavelength optical antennas, provide a method of meeting those requirements. Moreover, metalenses have many other distinctive advantages including aberration correction, active tunability, and semi-transparency, compared to their conventional refractive and diffractive counterparts. Therefore, over the last decade, great effort has been focused on developing metalenses to investigate and broaden the capabilities of metalenses for integration into future applications. Here, we discuss recent progress on metalenses including their basic design principles and notable characteristics such as aberration correction, tunability, and multifunctionality.

Characterization of Monochromatic Aberrated Metalenses in Terms of Intensity-Based Moments

“…Each cell is supposed to impart a controllable phase φ m to an incident optical field across its finite dimension. This is the case, for instance, for metalenses formed from anisotropic meta-atoms that can rotate with an azimuthal angle α in the metalens plane (see the inset of Figure 1 a); then, for circularly polarized incident fields φ m = ±2 α [ 4 , 31 ], the plus and minus signs corresponding to right- and left-circular polarizations, respectively. Thus, because the metasurface is not continuous but is formed from discrete unit cells, it is not possible to generate a continuous phase distribution φ id ( x ), even if the azimuthal angle α of the metalens varies continuously.…”

“…Metalenses, constituted from unit cells much smaller than the operating light wavelength, are particularly designed metasurfaces (see, for instance [ 1 , 2 , 3 , 4 , 5 ]) for focusing and imaging purposes. In the last years, metalenses have been thoroughly studied, different configurations of unit cells—meta-atoms—being proposed in order to improve their performances, in particular to minimize their chromatic as well as monochromatic aberrations [ 6 , 7 ].…”

“…In general, the estimation of aberrations is performed using ray tracing [ 15 , 16 , 17 ], generalizing the Debye integral and assigning specific aberration types to different Zernike polynomials [ 18 ] or assuming a certain expression of the phase distribution imparted by the metalens on an incoming optical field (see [ 4 , 19 ] and the references therein). Irrespective of the aberration type, its effect is to modify the beam shape in the focal plane of the metalens.…”

Artificial Compound Eye Systems and Their Application: A Review

“…However, an abrupt phase change at an interface, light can be arbitrarily deflected in any direction. Several reviews on the recent developments of metasurfaces have discussed the mechanism of different kinds of metasurfaces in detail [ 65 , 66 , 67 ]. With the nanostructure of metasurfaces, this kind of artificial compound eye imaging system is a more compact system than traditional types.…”

Near-Field Focusing With Subwavelength Thickness Metalenses via Electromagnetic Susceptibility Models

“…It has high-quality imaging capabilities, including sub-wavelength resolution and 31% focusing efficiency [4]. The metalens has remarkable characteristics such as aberration correction, active tunability and translucency [5], especially for near-field wavefront control, it has natural advantages (higher numerical aperture, ultra-high resolution). Near-field focusing imaging using surface waves has already been applied to a variety of near-field scanning scenes due to its extremely small half-width of the focal peak [6] [7] [8] [9].…”