Polarized structure color from thin dielectric gratings on an aluminum film is investigated. In the visible range, the −1st-order reflection of transverse electric (TE) light is higher than that of transverse magnetic (TM) light. Accordingly, the zeroth-order reflections for both polarizations behave distinctively such that TE-polarized light is chromatic while that for TM-polarized light is nearly white. Such chromatic and polarizing reflection predominantly comes from the Fabry-Perot interference between the interfaces of air/dielectric gratings and dielectric gratings/the metal region, which inhibits TM diffraction while facilitating TE diffraction. By further patterning the grating with a mask of an "apple," the central pattern is concealed when the polarization of the incident light is shifted from TE to TM. The characteristics of chromatic and polarizing reflection make this structure directly applicable in anticounterfeiting and decoration with the advantages of slim dimensions and easy fabrication.
An optical touch panel integrated with fingerprint recognition function has been proposed and confirmed. Through tactical design with slanted grating and appropriate pitch, efficient coupling of waveguide mode for touch sensing and sufficient non-overlapping area for fingerprint detecting were obtained simultaneously, meaning great potential for intelligent touch devices.
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