Plasmonics metalens independent from the incident polarizations.

An ultra-thin, planar, broadband metalens composed of L-shaped gap antennas on a thin gold film has been designed, which is suitable for both circular and X/Y linear polarizations focusing simultaneously. The phase discontinuity of the cross-polarized transmisson light can be manipulated by the length and width of the L-shaped gap antenna accurately. The designed planar metalens posses a strong focusing ability over a large wavelength range, and the size of the focus spot is in sub-wavelength scale. The focal lengths change from 13 to 7 um with incident wavelength from 750 to 1300 nm, and the cause of dispersion is explained and analyzed in detail. The designed metalens can work very well at a wide incident angles of 0~45°. Most importantly, its unique focusing ability that is independent of the incident polarizations will greatly promotes the practical applications and developments of the metasurfaces.