High efficient Al: ZnO based bifocus metalens in visible spectrum
Pengdi Wang(王鹏迪)1 and Xianghua Zeng(曾祥华)1,2,†
1College of Physics Science and Technology & Institute of Optoelectronic Technology, Yangzhou University, Yangzhou 225002, China 2College of Electrical, Energy and Power Engineering, Yangzhou University, Yangzhou 225127, China
The optical components of the visible light band are widely used in daily life and industrial development. However due to the serious loss of light and the high cost, the application is limited. The broadband gap metasurface will change this situation due to its low absorption and high efficiency. Herein, we simulate a size-adjustable metasurface of the Al doped ZnO (AZO) nanorod arrays based on finite difference time domain method (FDTD) which can realize the conversion of amplitude polarization and phase in the full visible band. The corresponding theoretical polarization conversion efficiency can reach as high as 91.48% (450 nm), 95.27% (530 nm), and 91.01% (65 nm). The modulation of focusing wavelength can be realized by directly adjusting the height of the AZO nanorod. The designed half-wave plate and metalens can be applied in the imaging power modulation halfwave conversion and enriching the spectroscopy.
* Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB0403101).
Cite this article:
Pengdi Wang(王鹏迪) and Xianghua Zeng(曾祥华)† High efficient Al: ZnO based bifocus metalens in visible spectrum 2020 Chin. Phys. B 29 104211
Fig. 1.
(a) Structure of the AZO unit cell. (b) The longitudinal cross-section of the AZO unit cell with a height of H. (c) The transverse section of the AZO unit cell, where L and W represent the length and width of AZO nanorod, and Ix, Iy represent the length and width of ITO substrate. (d) Crystal axes (fast axis and low axis) coincide with Ex and Ey of the incident wave. (e) The AZO nanorod rotated by θ. (f) AZO refractive index n, k diagram.
Fig. 2.
Polarization efficiency of the three structures, the incident light with left/right circled polarization and the transmission light with right/light circled polarization.
Fig. 3.
Polarization conversion efficiency versus wavelength for different AZO plates: (a) AZO plates with different width W; (b) AZO plates with different length L; (c), (d) substrates with different length Ix and width Iy, respectively.
Fig. 4.
(a) Schematic of polarity flip. (b)–(d) The relationship between the additional phase φ of the transmission field and the θ angle for samples S1 (450 nm), S2 (530 nm), and S3 (650 nm), respectively.
Structure
S1
S2
S3
Length (L)/nm
45
45
45
Width (W)/nm
90
90
90
Height (H)/nm
1400
1850
2600
Ix/nm
100
100
100
Iy/nm
100
100
100
Table 1.
Structure parameters of S1, S2, and S3.
Fig. 5.
Schematic of metalens designed according to PB phase method: (a) 1-D metalens, (b), (c) 2-D metalens.
Fig. 6.
The phase profiles of Ex and Ey for the three structures: (a) S1 (450 nm), (b) S2 (530 nm), (c) S3 (650 nm), where the left picture in (a)–(c) is corresponding to the one without AZO. At z = 4 μm, the retardation phase curves of Ex, Ey and their differences for (d) S1 (450 nm), (e) S2 (530 nm), (f) S3 (650 nm).
Wavelength
450
530
650
Ex (with structure)/π
20.321
17.601
14.939
Ex and Ey (without structure)/π
17.769
15.053
12.304
Ey (with structure)/π
19.125
16.446
13.802
Phase shift of Ex/π
2.552
2.548
2.635
Phase shift of Ey/π
1.356
1.393
1.498
Phase difference/π
1.196
1.155
1.137
Table 2.
Phase shift of Ex and Ey for linearly polarized incident light at 450 nm, 530 nm, and 650 nm with respect to Figs. 6(d)–6(f).
Fig. 7.
The 1-D AZO metalens designed based on Fig. 3(a) with a total transverse length of 20 μm, with a circularly polarized incident light. (a)–(c) The diagram of power distribution in the x–z plane for the S1 (450 nm), S2 (530 nm), and S3 (650 nm), respectively. (d)–(f) Normalized intensity diagrams based on the three images at z = 10 μm. (g)–(i) x–z plane phase profile diagram at y = 0 μm in the x–z plane.
Fig. 8.
The intensity distribution on x–z plane of 2-D metalens: (a) S1 (450 nm), (b) S2 (530 nm), (c) S3 (650 nm), the z coordinates of two focal points are marked on the graph. (d)–(i) The x–y section of intensity distribution diagram at corresponding z values (marked in the upper right corner).
Fig. 9.
(a)–(f) The normalized intensity diagram on the x-y plane at different z values corresponding to the six focal points in Figs. 8(d)–8(i).
Fig. 10.
The x–z cross-section intensity distribution of 2D-metalens with the S3 structure of AZO nanorods by the PB phase method: (a) 60 × 60 AZO nanorods, (b) 40 × 40 AZO nanorods.
Structure
FE of point 1
FE of point 2
NA of point 1
NA of point 2
S1
0.536
0.238
0.410
0.707
S2
0.606
0.273
0.430
0.725
S3
0.645
0.337
0.447
0.721
Table 3.
Focusing efficiency (FE) and NA of 2D-metalen with structures (S1, S2, S3) designed by PB phase method.
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