Third-harmonic generation and imaging with resonant Si membrane metasurface

Dielectric metasurfaces play an increasingly important role in enhancing optical nonlinear generations owing to their ability to support strong light-matter interactions based on Mie-type multipolar resonances.Compared to metasurfaces composed of the periodic arrangement of nanoparticles,inverse,so-called,membrane metasurfaces offer unique possibilities for supporting multipolar resonances,while maintaining small unit cell size,large mode volume and high field enhancement for enhancing nonlinear frequency conversion.Here,we theoretically and experimentally investigate the formation of bound states in the continuum(BICs)from silicon dimer-hole membrane metasurfaces.We demonstrate that our BIC-formed resonance features a strong and tailorable electric near-field confinement inside the silicon membrane films.Furthermore,we show that by tuning the gap between the holes,one can open a leaky channel to transform these regular BICs into quasi-BICs,which can be excited directly under normal plane wave incidence.To prove the capabilities of such metasurfaces,we demonstrate the conversion of an infrared image to the visible range,based on the Third-harmonic generation(THG)process with the resonant membrane metasurfaces.Our results suggest a new paradigm for realising efficient nonlinear photonics metadevices and hold promise for extending the applications of nonlinear structuring surfaces to new types of all-optical near-infrared imaging technologies.

Broadband infrared imaging governed by guidedmode resonance in dielectric metasurfaces

Nonlinear metasurfaces have experienced rapid growth recently due to their potential in various applications,including infrared imaging and spectroscopy.However,due to the low conversion efficiencies of metasurfaces,several strategies have been adopted to enhance their performances,including employing resonances at signal or nonlinear emission wavelengths.This strategy results in a narrow operational band of the nonlinear metasurfaces,which has bottlenecked many applications,including nonlinear holography,image encoding,and nonlinear metalenses.Here,we overcome this issue by introducing a new nonlinear imaging platform utilizing a pump beam to enhance signal conversion through four-wave mixing(FWM),whereby the metasurface is resonant at the pump wavelength rather than the signal or nonlinear emissions.As a result,we demonstrate broadband nonlinear imaging for arbitrary objects using metasurfaces.A silicon disk-on-slab metasurface is introduced with an excitable guided-mode resonance at the pump wavelength.This enabled direct conversion of a broad IR image ranging from>1000 to 4000 nm into visible.Importantly,adopting FWM substantially reduces the dependence on high-power signal inputs or resonant features at the signal beam of nonlinear imaging by utilizing the quadratic relationship between the pump beam intensity and the signal conversion efficiency.Our results,therefore,unlock the potential for broadband infrared imaging capabilities with metasurfaces,making a promising advancement for next-generation all-optical infrared imaging techniques with chip-scale photonic devices.