6. Birefringent Metamaterials for THz Optics

Terahertz (THz) region is typically referred to as the frequencies from 100 GHz to 30 THz, which lies between the infrared and microwaves. Since the typical wavelength of the THz wave is hundreds micrometer, we can easily fabricate the metallic structure with the size comparable with its wavelength, and the bulky three-dimensional metamaterial is not huge. Recent development of the ultrafast-pulse-laser technique allowed the generation and detection of the THz electromagnetic pulse, which has led to easy characterization of the medium with the time-domain spectroscopy. Therefore, there are many reports on the metamaterials in the THz frequency region. Metamaterials have been used as the practical optics in the THz region. Many materials are not transparent in this frequency region, so the artificial media based on the periodic structures of the metal such as the metal slit array and metal hole array have been developed. In this chapter, we review the recent advances of the metamaterials in the THz frequency region.