Full Complex‐Amplitude Engineering by Orientation‐Assisted Bilayer Metasurfaces

Abstract

through numerical calculation, one can encode the amplitude and phase of light waves into a CGH, and finally reconstruct the three-dimensional (3D) light field carrying object information through optical diffraction. In this process, a functional element with precise complex-amplitude modulation is the key to the digital encoding of holograms and the modulation of light waves. The modulation ability of light waves affects the numerical characteristics and reconstruction effect of holograms. An ideal complex-amplitude hologram can record the complex-amplitude information including the amplitude and phase of the object. However, since most of the existing optical elements such as conventional hologram recording with photographic negative, diffractive optical elements, and spatial light modulator (SLM) can only modulate the amplitude or phase of light wave, the hologram needs to be converted from the complex-amplitude to the pure amplitude or phase accordingly. With the development of new artificial materials such as metasurfaces, complex-amplitude hologram coding technology has attracted more and more attention due to its high spatial bandwidth product and high reconstruction accuracy.Optical complex-amplitude determines the propagation behavior of light in free space to the maximum extent. Precise control of complex-amplitude is the key to generating user-defined light fields. Current attempts to control optical complex-amplitude using metasurface, however, either have limited amplitude/phase step numbers or lost high lateral resolution since amplitude and phase are usually manipulated with size-varied nanostructures or several nanostructures integrated into a unit-pixel. Here, it is shown that bilayer metasurface can readily decouple optical amplitude and phase, thus achieving arbitrary complex-amplitude modulation only by arranging the orientation angles of nanostructures. In this design, each unit-pixel in one layer has only one nanostructure with the same size, thus significantly increasing the lateral resolution of complex-amplitude modulation. More importantly, the approach of controlling optical complex-amplitude merely by changing nanostructure orientation can significantly simplify the metasurface design and aggrandize the fabrication tolerance, thus enhancing the robustness of metasurfaces toward practical applications.

All-dielectric terahertz metasurfaces for arbitrary linear polarization detection

“…The height of the column is H = 400 µm, and the unit period is P = 140 µm. The time-domain solver of the commercial software CST MICROWAVE STUDIO is used to calculate the complex amplitude information of the meta-atoms with different geometrical parameters, in order to establishing a library of meta-atoms with different phase profiles [44][45][46]. In the simulation process, the x-and y-directions are set as periodic boundary conditions while the z-direction is set as open boundary condition.…”

Polarization detection for cylindrical vector beams empowered by pixelated metasurfaces

“…Recently, conventional optical devices for generating a variety of homogeneous polarization states have been miniaturized by using metasurfaces [9][10][11][12]. As quasi-periodic arrays of geometrically tailorable artificial building blocks, metasurfaces have the powerful ability to manipulate the polarization, phase, and frequency degrees of freedom of an optical field on the subwavelength scale, and have been successfully engineered for versatile applications such as meta-lenses [13][14][15], holography [16][17][18], and vortex generators [19][20][21].…”

Fabrication of Large-Area Nanostructures Using Cross-Nanoimprint Strategy

“…In recent years, with the continuous expansion of micro–nanofabrication application fields and the ongoing development of micro–nano optics and photonics, there has been a growing demand for large-area, high-precision micro–nanostructured devices such as optical waveguides [ 1 , 2 ], OLEDs [ 3 ], multifunctional image displays [ 4 , 5 ], photodetectors [ 6 ], biosensors [ 7 ], metalenses [ 8 , 9 ], and solar cells [ 10 ]. The high-precision manufacturing of these devices over large areas is a key challenge for the practical implementation of such technologies.…”