Super-broadband geometric phase devices based on circular polarization converter with mirror symmetry

We propose a simple implementation to obtain super-broadband geometric phase devices (GPD) by means of circular polarization converter (CPC) with mirror symmetry. We demonstrate that the best choice of wideband GPDs and CPCs is a mirror symmetric structure. Based on a two-rotation model on the Poincare sphere, optimization parameters and time are significantly reduced. The CPC can be extended to super-broadband GPD, such as polarization gratings (PGs), by using geometric phase holography. We simulate diffraction efficiencies of the super-broadband PGs. In the normal incident case, the diffraction efficiency is over 99% in 420-945 nm, and in the oblique incident case, the first-order diffraction efficiency is over 90% in the range of +/- 30 degrees. The super-broadband GPDs show potential advantages in wide color display and spectral imaging.