Large polarization change in two-dimensional metallic photonic crystals in subterahertz region

Interesting polarization characteristics of two-dimensional metallic photonic crystals (2D-MPC) in the subterahertz region have been found. We measured the temporal wave form of the THz wave transmitted thorough the 2D-MPC using a THz time domain spectroscopic system. The linear polarization of the incident THz wave transmitted through the 2D-MPC becomes elliptical with a slight tilting of the incident angle from the normal incidence. This result indicates that the 2D-MPC behaves not only as a band-pass filter already reported, but also as a wave plate. This large polarization change is attributed to the strong TE–TM polarization mixing in the 2D-MPC.