Directive giant upconversion by supercritical bound states in the continuum

• 成果类型: Article
• 署名作者: Schiattarella, Chiara; Romano, Silvia; Sirleto, Luigi; Mocella, Vito; Rendina, Ivo; Lanzio, Vittorino; Riminucci, Fabrizio; Schwartzberg, Adam; Cabrini, Stefano; Chen, Jiaye; Liang, Liangliang; Liu, Xiaogang; Zito, Gianluigi
• 署名单位: Consiglio Nazionale delle Ricerche (CNR); Istituto di Scienze Applicate e Sistemi Intelligenti Eduardo Caianiello (ISASI-CNR); Consiglio Nazionale delle Ricerche (CNR); Istituto di Scienze Applicate e Sistemi Intelligenti Eduardo Caianiello (ISASI-CNR); United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; National University of Singapore; Agency for Science Technology & Research (A*STAR); A*STAR - Institute of Materials Research & Engineering (IMRE); National University of Singapore
• 刊物名称: Nature
• ISSN/ISSBN: 0028-4312
• DOI: 10.1038/s41586-023-06967-9
• 发表日期: 2024-02-22
• 关键词: electromagnetically induced transparency; coupled-mode theory; enhancement

摘要

Photonic bound states in the continuum (BICs), embedded in the spectrum of free-space waves1,2 with diverging radiative quality factor, are topologically non-trivial dark modes in open-cavity resonators that have enabled important advances in photonics3,4. However, it is particularly challenging to achieve maximum near-field enhancement, as this requires matching radiative and non-radiative losses. Here we propose the concept of supercritical coupling, drawing inspiration from electromagnetically induced transparency in near-field coupled resonances close to the Friedrich-Wintgen condition2. Supercritical coupling occurs when the near-field coupling between dark and bright modes compensates for the negligible direct far-field coupling with the dark mode. This enables a quasi-BIC field to reach maximum enhancement imposed by non-radiative loss, even when the radiative quality factor is divergent. Our experimental design consists of a photonic-crystal nanoslab covered with upconversion nanoparticles. Near-field coupling is finely tuned at the nanostructure edge, in which a coherent upconversion luminescence enhanced by eight orders of magnitude is observed. The emission shows negligible divergence, narrow width at the microscale and controllable directivity through input focusing and polarization. This approach is relevant to various physical processes, with potential applications for light-source development, energy harvesting and photochemical catalysis. An experimental design consisting of a photonic-crystal nanoslab covered with upconversion nanoparticles demonstrates the phenomenon of supercritical coupling, resulting in giant enhancement of upconversion by photonic bound states in the continuum.