Begin with Maxwell Equation>>Spherical Symmetry -60 R 2 Appl.Phys.Lett.95,041106(2009) nd=const. Bigger n n=n( s0 2 2 2 rR d c n c      − = − −  n n r = ( ) Appl. Phys. Lett. 95, 041106(2009) nd const = . Bigger n!