Multiple Scattering and Random Quasi-Phase-Matching in Disordered Assemblies of LiNbO₃ Nanocubes

Abstract

Nonlinear disordered photonic media (NDPM), composed of a random configuration of noncentrosymmetric crystals, offer a versatile platform to tailor nonlinear optical effects. The second-harmonic generation (SHG) and its random quasi-phasematching (RQPM) in the multiple scattering regime are still poorly explored. In this work, we bottom-up assemble NDPM in two different geometries by using LiNbO 3 nanocubes as building blocks and investigate both the multiple scattering and the nonlinear properties. We produce disordered slabs with a continuously variable thickness and microspheres with different diameters, which display a remarkable strong light scattering, evidenced by a subwavelength transport mean free path ( * ). We first provide explicit evidence that the SHG power scales linearly with both the thickness of the slab and the volume of the microspheres. These observations generalize the characteristic linear scaling of RQPM power with the volume to the multiple scattering regime and to different sample geometries. Our structures represent a promising platform to investigate the interplay between disorder and optical nonlinear effects.

Second-harmonic generation based on single lithium niobate nanocrystals

“…除了上述电介质材料, 铌酸锂(LiNbO 3 )带隙高达 4 eV, 在光学波段具有很小的吸收系数, 同时具有非中 心对称的晶体结构, 二阶非线性系数超过−20 pm/V, 是一种重要的非线性材料 [30,31] , 广泛应用于片上光子 学器件的设计 [32][33][34][35][36] . 此外, 基于LiNbO 3 纳米颗粒同样 可以激发如磁偶极共振等米氏模式 [37] , 实验表明SHG 转换效率可以达到7.6×10 ).…”

Large-scale photonic computing with nonlinear disordered media

“…The slab not only scatters incoming light, but also simultaneously generates second-harmonic (SH) speckles mediated by random quasiphase-matching. 2,3 Using a spatial light modulator to encode an input and detecting on a camera, multiple scattering acts as random weights, thus the scattering of fundamental harmonic (FH) computes linear features akin to random projection. 4 The SH wave generated by the scattered pump is again subject to random scattering, defining a complex nonlinear photonic neural network in which the second-order nonlinearity acts as internal nonlinear activation functions.…”

All-Optical Domain Inversion in LiNbO3 Crystals by Visible Continuous-Wave Laser Irradiation

“…LN stands out for its high electrooptic coefficients with fast response, high nonlinear coefficients for second-order χ (2) and third-order χ (3) processes, strong photorefraction, and broad transparency window (350–5500 nm) . These remarkable properties make it possible to tailor this platform for a number of widespread photonic applications: electrooptic modulators, integrated spectrometers, hologram storage, frequency conversion, − frequency comb generation, , optofluidic lab-on-a-chip devices, , or various nonlinear nanophotonic applications, among others. Most of the aforementioned applications of LN are ultimately enabled by its noncentrosymmetric and ferroelectric nature.…”