Figure 2.
Malus’ law and image-hidden mechanism. (a) According to Malus’ law, when a linearly polarized light beam passes through an analyzer (linear polarizer), the intensity of light transmitted by the analyzer is I=I0cos2θ, where I0 is the intensity of incident light, and θ is the angle between the transmission axes of the analyzer and the polarizer. A grayscale image is hidden in the linear polarization profile of a light beam. (b) The target image of James Clerk Maxwell’s grayscale portrait. (c) The details of the selected area from the eyebrow area with 10×10 pixels. The left side shows the grayscale profile, and the right side shows the required polarization distribution for the analyzer with a transmission axis along the vertical direction. (d) A linear polarization is generated by a coherent superposition of two planar circularly polarized beams with opposite handedness, which propagates along the same direction. (e) As the sign of the geometric phase generated at the interface of metasurface only depends on the handedness of the incident light, under the illumination of a linearly polarized beam, the off-axis reflected beams with opposite handedness will meet, interfere with each other, and generate the desired polarization profile for the hidden image on both sides.