Experimental evidence of giant pure optical activity in a metasurface   based on a complementary twisted cross configuration
  This work presents an experimental study of giant and pure optical activity in a periodic structure consisting of twisted crosses and complementary crosses patterned on the sides of a copper coated dielectric board. Additionally, a multilayer system is proposed and numerically studied to broaden the transmission bandwidth. Our results show that a dual band behavior can be obtained due to coupling effects between the layers whilst maintaining the dispersionless giant optical activity and negligible circular dichroism. We theoretically study the effect of the separation between layers and its influence on the transmission spectra. 
Ana D\'iaz-Rubio, Ben Tremain, Jorge Carbonell, Jos\'e   S\'anchez-Dehesa and Alastair Hibbins
physics.optics