Nonlinear meta-optics towards applications

Abstract Nonlinear optical effects have enabled numerous applications such as laser frequency conversion, ultrafast electro-optical, and all-optical modulation. Both gaseous bulk media conventionally been used for free-space nonlinear applications, yet they often require complex phase-matching techniques efficient operation may limited bandwidth due to the material absorption. In last decade, meta-optics made of subwavelength antennas or films emerged novel that potentially overcome certain limitations crystals. Due resonant enhancements pump field well use materials with extreme nonlinearity epsilon-near-zero materials, can achieve strong responses a thickness. Here, we review several electric-field-induced second-harmonic generation, entangled photon pair terahertz modulation, high-harmonic generation envision distinct advantages over their counterparts. We outline challenges still faced by point out some potential directions.