Low-Loss Terahertz Artificial Dielectric Birefringent Quarter-Wave Plates

We have developed anisotropically etched low-loss artificial dielectric birefringent quarter-wave plates (QWPs) for use at 1.5 and 2.8 THz. The grating period for both QWPs is 20 m. We etched 46- and 30-m-deep gratings to obtain a phase retardance between transverse-magnetic and transverse-electric polarization propagating through the QWPs at 1.5 and 2.8 THz, respectively. A SU8 antireflection coating is used to further improve the transmission coefficient by up to 21%. The measured results from Fourier transform infrared spectroscopy show a good agreement with designed specifications.