  By numerical simulations, we show that properly arranged two dimensional
periodic arrays, formed by dielectric cylinders embedded in parallel in a
uniform medium, can indeed act as an optical lens to focus electromagnetic
waves, in accordance with the recent conjecture in the literature. The
numerical simulations are based on an exact multiple scattering technique. The
results suggest that the E-polarized waves are easier to be focused than the
H-polarized waves. The robustness of the focusing against disorders is also
studied. Comparison with the corresponding cases for acoustic waves is also
discussed.
