Second-Harmonic Generation in Resonant Nonlinear Metasurfaces Based on Lithium Niobate

Abstract

Lithium niobate is an excellent and widely used material for nonlinear frequency conversion due to its strong optical nonlinearity and broad transparency region. Here, we report the fabrication and experimental investigation of resonant nonlinear metasurfaces for second-harmonic generation based on thin-film lithium niobate. In the fabricated metasurfaces, we observe pronounced Mie-type resonances leading to enhanced second-harmonic generation in the direction normal to the metasurface. We find the largest second-harmonic generation efficiency for the resonance dominated by the electric contributions because its specific field distribution enables the most efficient usage of the largest element of the lithium niobate nonlinear susceptibility tensor. This is confirmed by polarization-resolved second-harmonic measurements, where we study contributions from different elements of the nonlinear susceptibility tensor to the total second-harmonic signal. Our work facilitates establishing lithium niobate as a material for resonant nanophotonics.

Photon Pairs from Resonant Metasurfaces

“…Since the QOM period is larger than the pump wavelength, diffraction into the first orders occurs, the zeroth order carrying only a fraction of the incoming pump power. 33 Photon pairs can be generated by each diffraction order of the pump; however, with our NA, we only collect pairs corresponding to the zeroth order. We believe that the measured photon-pair rate could be considerably increased by using optics with higher NA or modifying the QOM design.…”

Nonlinear Lithium Niobate Metasurfaces for Second Harmonic Generation

“…Only until recently, the barriers in fabricating the LN metasurfaces have been removed using the FIB and dry etching with great carefully adjusted processing parameters. [ 45–47 ] And efficient tuning over the spectral resonance through varying the structural parameters has been demonstrated, which makes it possible to resonantly control the SHG from the LN metasurfaces. Recently the properties of angular distributions of the SH from the LN metasurfaces have been studied.…”

“…Recently the properties of angular distributions of the SH from the LN metasurfaces have been studied. [ 47 ]…”

Electro-optic lithium niobate metasurfaces

“…And a variety of on-chip EO modulator units with tens to hundreds of GHz modulation speeds have been demonstrated using different LNOI microstructures, for example Mach-Zehnder interferometric waveguide [38,39], photonic crystals [40,41], micro-rings [42,43] or micro-disks [44]. Recent years have witnessed significant advances in fabricating LN metasurfaces [45,46] and consequently the demonstration of intriguing tunable second harmonic properties [47,48]. However, the EO modulation by an LN metasurface, to the best of our knowledge, has rarely been experimentally explored.…”