Three-dimensional Nanowire Photonics

Abstract

Photonics, the scientific study and application of light, has been revolutionizing our everyday life. Sharing the logic of miniaturization in electronics, enormous efforts have been directed to nanoscale photonic elements. Among them, nanowires possess exclusive significance in miniaturized photonics owing to the ability of light delivery that is vital for the realization of nanoscale photonic integration. However, utilizing nanowires in photonics encounter a critical issue known as substrate coupling, unwanted light interaction between nanowires and the underlying substrate. Substrate coupling causes not only the misleading in fundamental understandings, but also the degradation in application performances. In this dissertation, a revolutionary approach to nanowire photonics is presented, here named three-dimensional (3D) nanowire photonics, for fundamental understandings and versatile applications of nanowires. 3D nanowire photonics enables to overcome various confronted problems arising from the substrate coupling issue by exploiting 3D space for fabrication and manipulation of nanowires, in contrast to the conventional nanowire photonics limited within 2D space. First, for fundamental understandings, light propagation in nanowires is studied. Substrate coupling causes invalid estimation of fundamental characteristics of nanowires. Here 3D fabrication and manipulation of nanowires enabled valid characterizations of nanowires decoupled from substrate, which include propagation loss, bending loss, scale dependency of the two losses, self-absorption, and polarization anisotropy. In addition, the estimation of the substrate coupling loss was demonstrated for the first time. The implication of this work is significant because understanding of light propagation in nanowires is the first step for nanowire photonic researches and applications. Second, for versatile applications, photonic nanowire writing is developed. Contemporary technologies for nanoscale optical interconnection are relying on post- synthesis 2D assembly of nanowires that is limited by the substrate coupling issue and the destructive manipulation of nanowires. Here the 3D direct integration of photonic nanowires, named photonic nanowire writing (PNW), enabled direct optical interconnection with no substrate coupling for the first time. Also the versatility of PNW was demonstrated by the integration over a gap or a step, stretchable optical interconnection, and 3D branched structures for nanowire splitters and multiplexers. This work shall innovate photonic researches and industry by providing a powerful ground technology for nanoscale photonic integration with high performance, substantial versatility and unprecedented simplicity.