Shape-Controlled Assembly of Nanowires for Photonic Elements

We fabricated a single U-shaped nanowire (NW) and tangent-coupled straight and U-shaped NWs using a novel technique of shape-controlled deterministic assembly of NWs with nanoscale controllability. To examine the optical properties of these structures, we calculated the transmitted and crossover optical powers of the fundamental guided mode in both the single and coupled CdS NWs by varying the key structural parameters such as the radius of curvature of the U-shaped head and the gap between the NWs. In addition, we experimentally studied active waveguiding in the assembled CdS NWs, which exhibited light coupling to the waveguide mode and direct transmission in the single U-shaped NW. Furthermore, the crossover coupling was measured for the tangent-coupled straight and U-shaped CdS NWs with a gap width of 70 nm. The shape-controlled deterministic assembly technique can open up a new opportunity to demonstrate subwavelength-scale photonic waveguides and couplers in compact nanophotonic integrated circuits.