Polarization-insensitive dual-wavelength dispersion tunable metalens achieved by global modulation method

Abstract

Integrating a thermal imaging system equipped with an optical metalens other than a traditional lens into an unmanned aerial vehicle (UAV) will increase its endurance considerably. In the design of metalens, simultaneously controlling dispersion and polarization properties is significant. However, via a propagation phase modulation method in which the phase is tuned locally, it is difficult and time-consuming to obtain enough different nanostructures to control multiwavelength independently while maintain the polarization-insensitive property. To this end, by using a global modulation method, a polarization-insensitive dual-wavelength achromatic and super-chromatic metalens are designed respectively. Only the geometric parameters of two nanofins are required to be optimized (through genetic algorithm) to modulate dual-wavelengths. Then they are superimposed on each other to form cross-shaped meta-atoms. In order to control the influence between the two crossed nanofins, an additional term Δf is introduced into the phase equation to modify the shape of the wavefront, whereby the phase dispersion can be easily engineered. Compared with local modulation, the number of unique nanostructures that need to be optimized can be reduced to two (operating at dual wavelengths) by the Pancharatnam–Berry (PB) phase based global modulation method. Therefore, the proposed design strategy, characterized by its simplicity, efficiency, and timesaver, is expected to circumvent difficulties encountered in the local design approaches. This strategy holds significant potential for widespread applications in multiwavelength imaging and spectroscopy.