Million-Q Free Space Meta-Optical Resonator at Visible Wavelengths

TL;DR

This paper reports the design and fabrication of a free-space visible-wavelength metasurface with a record-high Q-factor of over a million, enabling advanced optical applications and quantum light control.

Contribution

The authors demonstrate a novel free-space metasurface resonator with ultrahigh Q-factor at visible wavelengths, overcoming fabrication challenges and introducing a new spectroscopy technique.

Findings

Achieved a million-Q resonance in free space metasurface.

Developed a high-resolution momentum-space spectroscopy method.

Observed linewidth narrowing with pump power at room temperature.

Abstract

High-quality (Q)-factor optical resonators with extreme temporal coherence are of both technological and fundamental importance in optical metrology, continuous-wave lasing, and semiconductor quantum optics. Despite extensive efforts in designing high-Q resonators across different spectral regimes, the experimental realization of very large Q-factors at visible wavelengths remains challenging due to the small feature size that is sensitive to fabrication imperfections, and thus is typically implemented in integrated photonics. In the pursuit of free-space optics with the benefits of large space-bandwidth product and massive parallel operations, here we design and fabricate a visible-wavelength etch-free metasurface with minimized fabrication defects and experimentally demonstrate a million-scale ultrahigh-Q resonance. A new laser-scanning momentum-space-resolved spectroscopy technique with extremely high spectral and angular resolution is developed to characterize the record-high Q-factor as well as the dispersion of the million-Q resonance in free space. By integrating monolayer WSe2 into our ultrahigh-Q meta-resonator, we further demonstrate laser-like highly unidirectional and narrow-linewidth exciton emission, albeit without any operating power density threshold. Under continuous-wave laser pumping, we observe pump-power-dependent linewidth narrowing at room temperature, indicating the potential of our meta-optics platform in controlling coherent quantum light-sources. Our result also holds great promise for applications like optical sensing, spectral filtering, and few-photon nonlinear optics.