Harmonic generation from 2D materials coupled to resonant metasurfaces

Abstract

There is interest in studying nonlinear optical properties of monolayer and few-layer 2D materials due to the inherently strong nonlinear optical properties, interesting symmetry properties and polarization dependence. However, the inherent ultrathin 2D material limits the interaction length and efficiency of the nonlinear optical process studied. To overcome this limitation, 2D materials are integrated with resonant photonic structures to increase the overall nonlinear optical interaction strength. Such heterogeneously integrated structures offer the advantage of combining a range of 2D materials exhibiting diverse linear and nonlinear optical properties with prefabricated photonic structures using simple dry-transfer or chemical vapor deposition techniques. Here we will discuss some of the recent progress made in the area of heterogenous integration of 2D materials with dielectric resonant structures. We will also describe some of our recent effort in this direction in the resonant enhancement of second harmonic generation (SHG) from multi-layer Gallium Selenide coupled to silicon twodimensional resonant metasurface to achieve polarization independent SHG enhancement. We find that the designed 2D silicon resonant structures exhibit field depolarization at the resonance wavelength which needs to be accounted for when analyzing the nonlinear polarization. Furthermore, the second-harmonic signal radiated from the structure exhibits higher order diffraction effects with strong incident polarization angle dependence for the higher order diffraction components. Experimental studies on the above structures are also discussed with the observation of resonant enhancement of SHG and similar polarization dependence of the SHG on-/ off- the resonant metasurface when restricting the collection angles to the zeroth order diffracted nonlinear signal.