Removal of surface plasmon polariton eigenmodes degeneracy

The effect of the tilt angle of a metal film on the transmissivity of subwavelength holes in optically thick metal film is investigated. We found that the transmission efficiency can be highly dependent on the tilt angle. It is also found that when the input photons are not polarized along the eigenmode directions of surface plasmon polariton, a birefringent phenomenon is observed when a periodic array 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.