Ultra-sharp Plasmonic Super-cavity Resonance and Light Absorption

Nano-structured metals have attracted a great amount of attention in recent years due to the exciting plasmonic and photonic properties. However, the intrinsic high loss of the metals inevitably leads to the low-Q plasmonic resonance, hampering numerous applications on optoelectronics. Here, we demonstrate an ultra-sharp light absorber platform by an optical nano-cavity coupled plasmonic grating. The introduced dielectric nano-cavity not only provides strong optical field localization with the incident light but also enhances the hybridization coupling with the surface plasmons of the metal nano-structure, which eventually produces the plasmonic super-cavity resonance with the spectral bandwidths down to sub-nanometer scale and the spectral Q factor up to ~1 03. Moreover, the spectral slope reaches 52.8%/nm, indicating a sharp lineshape. Near-unity absorption with A of 99.7% is simultaneously achieved. These features suggest the designing such plasmonic-photonic hybridized super-cavity structure being a promising route for achieving ultra-sharp light absorber, which can be utilized as subtractive monochromatic filters, plasmonic and optical switch devices, photo-thermal sensors, and biochemical detectors.