Abstract
Two-dimensional transition-metal dichalcogenide monolayers have remarkably large optical nonlinearity. However, the nonlinear optical conversion efficiency in monolayer transition-metal dichalcogenides is typically low due to small light–matter interaction length at the atomic thickness, which significantly obstructs their applications. Here, for the first time, we report broadband (up to ∼150 nm) enhancement of optical nonlinearity in monolayer MoS2 with plasmonic structures. Substantial enhancement of four-wave mixing is demonstrated with the enhancement factor up to three orders of magnitude for broadband frequency conversion, covering the major visible spectral region. The equivalent third-order nonlinearity of the hybrid MoS2-plasmonic structure is in the order of 10–17 m2/V2, far superior (∼10–100-times larger) to the widely used conventional bulk materials (e.g., LiNbO3, BBO) and nanomaterials (e.g., gold nanofilms). Such a considerable and broadband enhancement arises from the strongly confined electric field in the plasmonic structure, promising for numerous nonlinear photonic applications of two-dimensional materials.
Highlights
Two-dimensional transition-metal dichalcogenide monolayers have remarkably large optical nonlinearity
Nonlinear optics in the nanoscale regime has attracted massive attention in the last decades.[1]. It provides a host of fascinating phenomena,[2] which are remarkably useful for photonic applications such as ultrafast pulse generation.[3−5] Among various nonlinear optical processes, four-wave mixing (FWM), a third-order optical nonlinear process, plays a key role for a large range of applications.[6,7]
All these results show the great potential of using transition-metal dichalcogenides (TMDs) for diverse on-chip nonlinear optical devices, fundamentally different from those based on traditional bulk materials.[1,25]
Summary
Attributed to the plasmonic enhancement, the equivalent t|χh(e3)|eoqrdoefrMoofS210in−17themh2/yVbr2i,dwMhiocSh2-pislasamlmoonsict structure is one order in of magnitude larger than the previous results and far better than the conventional nonlinear optical materials (such as LiNbO3, BBO, Tables 1 and 2 in the Supporting Information).[1] To further improve the FWM enhancement, we can optimize the nanostructures for improved field enhancement (e.g., shrink the periodicity with a higher filling fraction of nanostructures, narrow down the gap within the bowtie). We can integrate the hybrid MoS2-plasmonic structures into an optical cavity or a waveguide to improve the enhancement
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