Giant second-harmonic generation in ferroelectric NbOI2

Abstract

Implementing nonlinear optical components in nanoscale photonic devices is challenged by phase matching conditions requiring thickness in the order of hundreds of wavelengths and disadvantaged by the short optical interaction depth of nanometer-scale materials and weak photon-photon interactions. Here we report that ferroelectric NbOI2 nanosheets exhibit giant SHG with conversion efficiencies that are orders of magnitude higher than commonly reported nonlinear crystals. The nonlinear response scales with layer thickness and is strain-and electrical-tunable; a record >0.2 % absolute SHG conversion efficiency and an effective NL susceptibility 𝜒 !"" ($) in the order of 10 −9 m V -1 are demonstrated at average pump intensity of 8 kW/cm 2 . Due to the interplay between anisotropic polarization and excitonic resonance in NbOI2, the spatial profile of the polarized SHG response can be tuned by the excitation wavelength. Our results represent a new paradigm for ultrathin, efficient NL optical components.

Analytical and numerical modeling of optical second harmonic generation in anisotropic crystals using ♯SHAARP package

“…unsuitable for nonlinear optical frequency conversion applications due to their substantial absorption. Since utilizing photon energies below the bandgap is required for nonlinear optical frequency conversion applications, any direct comparison of TaAs or similar absorbing materials to transparent LiNbO 3 is not meaningful 69 . The amplitude of the overall dielectric permittivity (presented as Uni( ε j j)) provides a closer estimation of the intrinsic properties as compared with the non-absorbing case.…”

Chirality logic gates

“…Toward future practical applications, we need to enhance the nonlinear conversion efficiency. We note that high nonlinear optical conversion efficiency has been reported in 2D materials [e.g., up to >0.2% in NbOI 2 nanosheets ( 43 )], which shows possibilities of further increasing the conversion efficiency with suitable 2D materials for practical applications. As demonstrated here, the operation principle also applies to bulk materials, which enriches the highly nonlinear optical material selection option.…”

“…According to the conservation of angular momentum in nonlinear optics such as third-harmonic generation ( 27 ), SFG ( 28 ), SHG ( 43 ), and two-photon photoluminescence processes ( 26 ), the allowed nonlinear processes by threefold rotational symmetry can be expressed as σ OUT ℏ − σ IN ℏ = 3 N ℏ. As shown in the top inset of Fig.…”

High-dimensional orbital angular momentum entanglement from an ultrathin nonlinear film

“…The generation efficiency can optimised by using the nonlinear material with the giant second-harmonic generation [45]. Recently, metasurfaces offer an ultracompact and versatile platform for enhancing nonlinear optical processes by designing Bound State in the Continuum (BIC) resonances, which support a confinement of the optical field within the nonlinear material [46,47].…”