15:30 〜 15:45
▲ [13p-B409-8] Demonstration of spin-momentum locking and broadband light trapping in adiabatic plasmonic grating
キーワード：spin-orbit interactions, plasmonics, light trapping
The rapid development of plasmonics and metamaterials enriches the interpretation of various phenomena in light-matter interaction. Very recently, the evanescent wave mediated spin-momentum (propagation direction) locking phenomenon is demonstrated by several types of nanophotonic structures, revealing the great potential in applications of planar lightwave circuit, quantum optics, and topological photonics. However, the ultrashort propagation time (~fs) in nanostructures hampers the further enhancement of such weak spin-orbit interactions and the functionality realization in nanophotonic applications. Here, we proposed a numerical study based on an adiabatic plasmonic grating to solve this problem, resulting in spin-momentum locking and broadband light trapping (ultraslow wave) at the same time. In Fig.1(a), a one-dimensional Ag grating with gradually changed depth is designed for broadband light trapping, according to the cut-off frequency supporting by the depth-dependent dispersion relation in Ag grating. As a result, the different frequency components of the broadband light source (electric dipole, iridescent dot in Fig.1(a)) are spatially separated and trapped at regions with the corresponding grating depth (top inset of Fig.1(a)), the so-called “trapped rainbow” phenomenon in plasmonics and metamaterials. While the handedness of light source (circular polarization) is considered, the plasmonic grating imparts the property of spin-momentum locking to the broadband light trapping (Fig.1(a,b)). Our study effectively extends and improves the spin-related functionalities in the existing nanophotonic applications like optical delay lines, isolators, and circulators.