Other Abstract | In the traditional optical imaging systems, lenses mainly rely on the principle of phase modulation caused by different thickness in the propagation of light to realize the function of focusing and imaging, which has strict requirements on the shape and thickness of lens, and thus is not conducive to the integration and lightweight of the optical system.
Metasurface is a kind of arrayed film devices, which is composed of sub-wavelength unit structures. It is also called two-dimensional metamaterial. Metasurface can flexibly control the basic information of electromagnetic waves, such as amplitude, polarization, phase, and so on, with the interaction between its sub-wavelength unit structure array and electromagnetic beam. Compared with traditional optical lenses, meta-lens are widely used in planar imaging, holography, beam shaping, super-resolution lithography and other fields due to their advantages such as lightweight, conformal plane and easy integration. Therefore, meta-lens is expected to break through the limitation on shape and thickness of traditional optical lens , and become the novel optical devices.
However, in practical imaging applications, a single-layer meta-lens can only modulate a beam with a small angle of incidence, while the off-axis aberration is severe, which greatly limits the imaging application of the meta-lens. In order to obtain the information of object space in a larger field of view and realize large field of view imaging, the limited field of view of meta-lens is analyzed and researched in this paper. In the ultraviolet and visible regions, two solutions to the limited field of view of meta-lens are proposed, which as follows:
1. At 375nm of ultraviolet light, a polarization-independent cascade meta-lens doublet is designed. The propagation phase is used as the phase modulation method of unit structures in the meta-lens. The polarization-independent focusing and imaging with resolution approximating the diffraction limit in the 60 degree field of view are realized by two aspheric phase modulations on linearly polarized incident light with different sizes of titanium dioxide nano-cylinders.
2. At 532±5nm waveband of visible light, the three-layer cascade meta-lens based on geometric phase is designed. Left circularly polarized incident light is modulated by different rotational titanium dioxide rectangular nano-cylinder units, and the focus and imaging with a bandwidth of 10nm and 90 field of view with resolution approximating the diffraction limit are achieved. |
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