Dielectric longitudinal bifocal metalens with adjustable intensity and high focusing efficiency.

Metalens recently attracts enormous attention due to its microscale figure and versatile functionalities. With the combination of geometric phase and propagation phase, we first wrote the phase equation of bifocal metalens that can high efficiently focus incidence into one or two foci in tandem along longitudinal direction, depending on the polarization of incidence. More importantly, the relative intensity of the two foci can be modulated conveniently by changing the ellipticity of incidence, which is different from previous bifocal metalenses need to be repatterned for each kind of relative intensity [Opt. Express23, 29855 (2015)]. Besides, the focusing efficiency of the proposed metalens is as high as 72%, and the separate distance between those two foci can be designed at will, which may find itself significant applications in optical tomography technique, optical data storage, and so on.