  We investigate the mechanism of extraordinary optical transmission in
subwave-length metal hole arrays. Experimental results for the arrays
consisting of square or rectangle holes are well explained about the dependence
of transmission strength on the polarization direction of the incident light.
This polarization dependence occurs in each single-hole. For a hole array,
there is in addition an interplay between the adjacent holes which is caused by
the transverse magnetic field of surface plasmon polariton on the metal film
surfaces. Based on the detailed study of a single-hole and two-hole structures,
a simple method to calculate the total tranmissivity of hole arrays is
proposed.
