  The effect of the tilt angle of metal film on the transmissivity of
subwavelength holes in optically thick metal film is investigated. The
transmission efficiency is found can be highly dependent on the tilt angle. It
is also found that when the input photons are polarized not along the eigenmode
directions of surface plasmon polariton, a birefringent phenomenon is observed
when the array with periodic of subwavelength holes is tilted. Linear
polarization states can be changed to elliptical polarization states and a
phase can be added between two eigenmodes. The phase is changed with the tilt
angle. A model based on surface plasmon polariton eigenmodes degeneracy is
presented to explain these experimental results.
