Enhanced second-harmonic generation from two-dimensional MoSe2 on a silicon waveguide

Abstract

Two-dimensional transition-metal dichalcogenides (TMDCs) with intrinsically broken crystal inversion symmetry and large second-order nonlinear responses have shown great promise for future nonlinear light sources. However, the sub-nanometer monolayer thickness of such materials limits the length of their nonlinear interaction with light. Here, we experimentally demonstrate the enhancement of the second-harmonic generation from monolayer MoSe2 by its integration onto a 220-nm-thick silicon waveguide. Such on-chip integration allows for a marked increase in the interaction length between the MoSe2 and the waveguide mode, further enabling phase matching of the nonlinear process. The demonstrated TMDC–silicon photonic hybrid integration opens the door to second-order nonlinear effects within the silicon photonic platform, including efficient frequency conversion, parametric amplification and the generation of entangled photon pairs. Combining two-dimensional materials with a silicon waveguide imparts silicon chips with desirable nonlinear optical effects. Two-dimensional transition-metal dichalcogenides exhibit large second-order responses, making them promising as nonlinear light sources, but their subnanometer thickness limits their nonlinear interaction with light. A European−Australian collaboration found that silicon slab waveguides topped with a layer of the transition-metal dichalcogenide MoSe2, a well-known two-dimensional material, produce enhanced second-harmonic generation. This is due to that the evanescent field of the silicon waveguide modes couple with MoSe2, which enables large second-order nonlinear response. Calculations indicate that a 1-mm-long waveguide could provide a second-harmonic signal that is 500 000 times larger than that obtained by pumping the MoSe2 monolayer from above. Other nonlinear effects such as wavelength conversion, parametric amplification and the generation of entangled photons should also be possible.