2, The Pennsylvania State University, University Park, Pennsylvania, United States
3, Air Force Research Laboratory (AFRL), Dayton, Ohio, United States
Simple metallic mirrors flip the spin of a circularly polarized wave upon normal incidence by inverting the direction of the propagation vector. Altering or maintaining the spin and polarization of waves carrying data is a critical need to be met at the brink of photonic information processing. In this work, we report a chiral metamaterial mirror that strongly absorbs a circularly polarized wave of one spin state and reflects that of the opposite spin in a manner conserving the circular polarization. A circular dichroic response in reflection as large as ~0.5 is experimentally observed in a near infrared wavelength band. By imaging a fabricated pattern composed of the enantiomeric unit cells, we directly visualize the two key features of our engineered meta-mirrors, namely the chiral-selective absorption and the polarization preservation upon reflection. Beyond the linear regime, the chiral resonances enhance light-matter interaction under circularly polarized excitation, greatly boosting the ability of the metamaterial to perform chiral-selective signal generation and optical imaging in the nonlinear regime. Chiral meta-mirrors, exhibiting giant chiroptical responses and spin-selective near field enhancement, hold great promise for applications in polarization sensitive electro-optical information processing and biosensing.