We have demonstrated how dielectric planar chiral surfaces can both modulate the intensity and change the polarization state of visible light diffracted from patterned surfaces. These effects are shown to be dependent on the sense of chirality of the surface and the input polarization state of the light. Individual diffracted beams can show variations of over 30% in their intensities for different input polarization states while opposite enantiomeric structures can exhibit differences of over 50%. The size of these effects could make these surfaces particularly promising candidates for the development of solid-state polarization-state detectors. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1944211͔Metallic planar chiral metamaterials with characteristic length-scales of a few microns have attracted significant interest recently in light of their novel and intriguing polarization properties. 1,2 Most notable of these is their ability to rotate and elliptize the polarization state of light. These effects were first observed for visible light diffracted in reflection from samples consisting of regular arrays of gammadion-shaped holes etched into thin metallic films 3 and were similar in form to effects that had been predicted for somewhat larger structures designed to operate in the microwave regime. 4 The underlying mechanism for these effects has previously been ascribed, at least in part, to the generation of induced currents or surface-plasmon-polaritons ͑SPP͒ in the walls of the metallic gammadions. 1,2 However, we will now demonstrate that similar effects are observable for visible light diffracted from patterned polymer films, suggesting that other mechanisms ͑such as electro-magnetic displacement currents or Fabry-Perot interference effects͒ may also play a significant role. More importantly, these results suggest that most patterned thin films that exhibit twodimensional chirality 5 could be capable of exhibiting polarization sensitive effects, irrespective of the physical properties of the medium in which the chiral pattern is formed.The global significance of these results is that they allude to the possibility of the creation of truly nonreciprocal optical structures from materials that are inherently nonmagnetic. Such effects have been predicted theoretically for a number of idealized physical structures subject to various preliminary assumptions and approximations, 4,6,7 but if they could be demonstrated experimentally for real structures they would undoubtedly prove crucial for the development of entirely new optical devices such as polarization sensitive detectors, manipulators, and other optical elements. Unfortunately, our attempts to realize such a device have so far failed to show any chirality-induced polarization change in the zero-order beam in either reflection or transmission when the sample is illuminated at either normal incidence or glazing incidence. However, other workers studying sub-wavelength structures ͑in which the average separation of the chiral elements, ⌳, is less tha...