The metasurface[
Chinese Optics Letters, Volume. 19, Issue 5, 053601(2021)
Independent phase manipulation of co- and cross-polarizations with all-dielectric metasurface
Phase carried by two orthogonal polarizations can be manipulated independently by controlling both the geometric size and orientation of the dielectric nanopost. With this characteristic, we demonstrate a novel multifunctional metasurface, which converts part of the incident linearly polarized light into its cross-polarization and encodes the phase of the two orthogonal polarizations independently. A beam splitter and a bifocal metalens were realized in a single-layer dielectric metasurface by this approach. We fabricated the bifocal metalens and demonstrated that two focal spots in orthogonal polarizations can be separated transversely or longitudinally at will. The proposed approach shows a new route to design multifunctional metasurfaces with various applications in holography and three-dimensional display.
1. Introduction
The metasurface[
By integrating diverse functionalities into one single device, the multifunctional metasurface[
In this paper, we present a new strategy to independently control the phase of two orthogonal polarizations with an all-dielectric metasurface. Part of the linearly polarized incident light is converted into the cross-polarization and the phase of co- and cross-polarized light can be coded independently by modifying the geometric size and orientation of the elliptical nanopost. Unlike the function of the polarization beam splitter, which deflects two eigen polarizations to different directions, our designed metasurface splits the linearly polarized incident light into two output beams with co- or cross-polarization and propagation along different directions [Fig. 1(a)]. Thereafter, a bifocal metalens, which focuses linearly polarized incident light onto two different positions, is demonstrated [Fig. 1(b)], and the polarization of two focal spots is co- and cross-polarized to the incident polarization, respectively. Moreover, the proposed method provides an intuitive approach for three-dimensional (3D) display, which needs to record a pair of orthogonally polarized images from a same scene in different perspectives simultaneously to convey depth perception for binocular stereo vision, encoding two offset images for co-polarized and cross-polarized light, respectively. In general, this method will pave a new route to design multifunctional metasurfaces and have various applications in holography and multi-image systems.
Sign up for Chinese Optics Letters TOC Get the latest issue of Advanced Photonics delivered right to you!Sign up now
Figure 1.Schematic illustrations of the multifunctional metasurface. (a) The designed metasurface splits the x-polarized incident light into two different directions. (b) The designed metalens focuses the x-polarized incident light on two independent focal spots.
2. Principle of Independent Phase Manipulation for Orthogonal Polarizations
Figure 2(a) presents the unit cell composed of the elliptical amorphous silicon (
Figure 2.Optical response for elliptical cylinder at freespace wavelength of 633 nm. All of the phases are in units of rad/π. (a) Schematic of the Si elliptical cylinder located on the quartz with parameters P = 300 nm, H = 410 nm, Do and De. (b) Schematic of the meta-atom optical response. (c), (d) Phase and amplitude of
It is noted that the phase delay
3. Simulation and Experimental Results of the Designed Metasurfaces
As a verification of independent phase manipulation for orthogonal polarizations, we designed a metasurface for splitting and deflecting the orthogonally polarized beams. As shown in Fig. 3(a), sixteen specific cells with different geometric sizes are arranged to constitute a supercell for the deflector. Under
Figure 3.Simulation results of the metasurface for splitting and deflecting the orthogonal polarization beam. (a) The supercell consisting of sixteen specific nanoposts. (b), (c) The phase delay φxx and φyx and their corresponding transmission of selected sixteen cells. The black line is the theoretically requested phase delay. (d), (e) The electric field contributions of x-polarization and y-polarization in the x–z plane with x-polarized incident light.
The different deflections for
Furthermore, we design a bifocal metalens, which converts part of the incident
The origin of the coordinate system is located at the center of the metalens, and focal parameters
The bifocal metalenses were fabricated on a fused silica substrate by electron beam lithography and inductively coupled plasma (ICP) reactive ion etching techniques. A typical scanning electron microscope (SEM) image of the metalens is presented in Fig. 4(a), where the diameter of the sample circle is 30 µm, containing 100 nanoposts along the diameter of the metalens.
Figure 4.(a) Top-view SEM image of the metalens. (b) Enlarged SEM image of the metalens in (a). (c) The measurement setup for image reconstruction and polarization characterization of the focal field.
The partially enlarged view of the SEM image [Fig. 4(b)] shows high quality of the fabrication, and the geometric size and orientation of each nanopost are accurately controlled. Figure 4(c) presents the schematic diagram of the experimental setup used for the optical characterization of the metalens. The incident light is from a supercontinuum laser (NKT “superK,” wavelength from 400 to 700 nm) equipped with a set of acousto-optic tunable filters (NKT “Select”) to output a 633 nm laser. After a Glan prism, the linearly polarized light is focused by a glass lens (
Figure 5 presents scanning confocal images and simulation results in the longitudinal section of four bifocal metalenses with different focal parameters. As shown in Fig. 5(a), the first bifocal metalens has the focal length of
Figure 5.Scanning confocal images and simulation results of the focal spots in the longitudinal section for four metalenses. (a), (b) Two focal spots of the metalenses are transversely separated. The insert is normalized optical intensity distribution along the dashed line. (c) The focal spots of the metalens are longitudinally separated. (d) The focal spots of the metalens are transversely and longitudinally separated simultaneously. (e)–(h) The corresponding x–z plane simulation results of metalenses in (a)–(d).
The polarization of the focal field is characterized by rotating the polarizer before the CCD detector. Without loss of generality, the optical field distributions at the focal plane (40 µm away from the metalens) for the first bifocal metalens are illustrated in Fig. 6. Figure 6(a) shows the normalized optical intensity distribution in the focal plane, indicating two separated spots.
Figure 6.(a) Normalized optical intensity distribution in the focal plane of the first metalens. (b)–(d) The normalized optical intensity distribution in the focal plane of the metalens, inserting a polarizer after the collected objective.
It is noted that the two focal spots [Figs. 5 and 6(a)] have different intensities, which can be further optimized by an algorithm of the structure’s dimensional searching. As shown in Fig. 7, we design a bifocal metalens under the prerequisite of
Figure 7.Simulation result of the metalens with same intensity and shape. (a), (b) The normalized optical intensity distributions in the x–z plane and the focal plane. (c) The normalized optical intensity distribution along the dashed line.
4. Discussion
In summary, we presented a birefringent metasurface to manipulate the phase of the two orthogonal polarizations independently. The metasurface was composed of
[21] H. Lv, X. Lu, Y. Han, Z. Mou, S. Teng. Multifocal metalens with a controllable intensity ratio. Opt. Lett., 44, 2518(2019).
Get Citation
Copy Citation Text
Haoyu Wang, Zhiyu Zhang, Kun Zhao, Wen Liu, Pei Wang, Yonghua Lu, "Independent phase manipulation of co- and cross-polarizations with all-dielectric metasurface," Chin. Opt. Lett. 19, 053601 (2021)
Category: Nanophotonics, Metamaterials, and Plasmonics
Received: Sep. 8, 2020
Accepted: Nov. 10, 2020
Posted: Nov. 11, 2020
Published Online: Mar. 3, 2021
The Author Email: Yonghua Lu (yhlu@ustc.edu.cn)