Near-field out-of-plane coupling between terahertz photonic crystal waveguides

Abstract

Terahertz-range photonic crystal waveguides composed of intrinsic silicon are showing promise as an efficient and versatile waveguiding platform for diverse applications. Compact terahertz systems that are founded upon this platform will benefit from near-field links in order to serve as general-purpose connectors and allow devices to be modular. To this end, we present near-field contactless signal power transfer between terahertz-range photonic crystal waveguides in the out-of-plane dimension. This is achieved by means of coupled-line techniques. It is found that the use of photonic crystal waveguides, in lieu of more conventional photonic waveguides, leads to an enhancement of the coupling effect. For the purpose of experimentation, a custom-machined sample holder is devised in order to secure the relative positioning of the photonic crystal waveguides and ensure repeatable alignment. It is found that the coupling efficiency of the near-field link in isolation is close to unity, and the bandwidth of the entire structure is ∼21 GHz, centered at 325 GHz. This proves sufficient to support multi-gigabit per second terahertz-range communications with a simple on-off-keying modulation scheme. As such, this demonstration validates the applicability of this vertical-coupling technique to practical applications of terahertz technology. Furthermore, the machined sample holder may lead to a much-needed packaging strategy for future silicon microphotonic systems.