True-colour images by subwavelength gratings
23.11.2010 - Photonik international /2010 | [ deutsche Version lesen ]
Gratings with periods smaller than visible wavelengths exhibit colourising effects in the zeroth diffraction order when its profile is designed so that electromagnetic resonances are excited on the grating. These resonances have a spectral selective influence to the light spectrum and allow colour filtering of even unpolarised white light. Apart from well-known resonances in TM polarisation, novel resonances in TE polarisation predominately contribute to colourising of wire gratings. The hue can be adjusted by the modulation depth of the wire profile. True-colour images can be generated by this kind of gratings having a laterally tailored modulation depth. This technique is advantageous for industrial mass production, and more practical applications, such as those for security features, will develop.
Authors: Hans Lochbihler, Papierfabrik Louisenthal GmbH, Gmund, Germany