Large phase differences between TE and TM waves were investigated in plasmonic nanowire arrays. The phase of the TE wave shifts ahead because of its low propagation constant. On the other hand, the phase of the TM wave is retarded due to the propagation of surface plasmons. The opposite phase shift forms the giant birefringence. Its magnitude was dependent on the nanowire width. For 500nm-period gold nanowires, the birefringence magnitude was ~1 for 200nm-wide nanowires and up to ~2.7 for 400nm ones. The spectroscopic results indicate that waveplates made of gold nanowire arrays have large bandwidths.
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