Tunable unidirectional nonlinear emission from transition-metal-dichalcogenide metasurfaces

• Published in: Nature communications Vol. 12; no. 1; p. 5597
• Main Authors: Nauman, Mudassar, Yan, Jingshi, de Ceglia, Domenico, Rahmani, Mohsen, Zangeneh Kamali, Khosro, De Angelis, Costantino, Miroshnichenko, Andrey E., Lu, Yuerui, Neshev, Dragomir N.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.09.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 132/122; 140/125; 142/126; 147/135; 639/624/399/1015; 639/925/357/1018; Chalcogenides; Dielectrics; Emission; Emissions; Harmonic generations; Harmonic radiation; Humanities and Social Sciences; Light; Light sources; Magnetic fields; Metasurfaces; Miniaturization; multidisciplinary; Refractivity; Science; Science (multidisciplinary); Semiconductors; Spectrum analysis; Transition metals
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-25717-x

Nonlinear light sources are central to a myriad of applications, driving a quest for their miniaturisation down to the nanoscale. In this quest, nonlinear metasurfaces hold a great promise, as they enhance nonlinear effects through their resonant photonic environment and high refractive index, such as in high-index dielectric metasurfaces. However, despite the sub-diffractive operation of dielectric metasurfaces at the fundamental wave, this condition is not fulfilled for the nonlinearly generated harmonic waves, thereby all nonlinear metasurfaces to date emit multiple diffractive beams. Here, we demonstrate the enhanced single-beam second- and third-harmonic generation in a metasurface of crystalline transition-metal-dichalcogenide material, offering the highest refractive index. We show that the interplay between the resonances of the metasurface allows for tuning of the unidirectional second-harmonic radiation in forward or backward direction, not possible in any bulk nonlinear crystal. Our results open new opportunities for metasurface-based nonlinear light-sources, including nonlinear mirrors and entangled-photon generation. Though high-index dielectric metasurfaces are attractive due to their nonlinear effects, channelling of 2 nd and 3 rd harmonic generation into a single beam remains a challenge. The authors addressed this using transition-metal-dichalcogenide metasurfaces with tunable nonlinear emission direction.