 Circular birefringence causes rotation of the polarization state of electromagnetic waves in chiral media and can cause a negative index of refraction for waves of one handedness when the effect is sufficiently large.While optical activity occurs in structures that are chiral in three dimensions (such as helices), the concept of chirality can also be applied in two dimensions.2D-chiral patterns, such as flat spirals, cannot be superimposed with their mirror image by translation or rotation in two-dimensional space (a plane).