Abstract-Terahertz multi-beam antenna using photonic crystal waveguide and Luneburg lens

APL Photonics

Daniel Headland,  Withawat Withayachumnankul, Ryoumei Yamada, Masayuki Fujita,  Tadao Nagatsuma,

Luneburg lens concept, showing the reciprocal principle of operation that relates a point on the circumference to a plane wave on the opposite side. It is noted that this behavior is represented with a ray-tracing diagram, but in practice, the lens must be significantly larger than a wavelength for this to be truly valid.

https://aip.scitation.org/doi/abs/10.1063/1.5060631

Recent years have seen the emergence of efficient, general-purpose terahertz photonic-crystal waveguides etched from high-resistivity silicon. Systems founded upon this platform will require antennas in order to interface with free-space fields. Multi-beam antennas are desirable to this end, as they are capable of interacting with a number of distinct directions simultaneously. Such functionality can be provided by Luneburg lenses, which we aim to incorporate with the terahertz photonic crystal waveguide. A Luneburg lens requires a precisely defined gradient-index, which we realize using effective medium techniques that are implemented with micro-scale etching of silicon. Thus, the photonic crystal waveguides can be integrated directly with the Luneburg lens and fabricated together from the same silicon wafer. In this way, we develop a planar Luneburg-lens antenna with a diameter of 17 mm and seven evenly spaced ports that cover a 120° field of view. Numerical and experimental characterization confirm that the antenna functions as intended over its operation bandwidth, which spans from 320 to 390 GHz. The Luneburg-lens antenna is subsequently deployed in a demonstration of terahertz communications over a short distance. The device may therefore find applications in terahertz communications, where multiple point-to-point links can be sustained by a given transceiver node. This form of terahertz beam control may also be useful for short-range radar that monitors several directions simultaneously.