Multiple Sharp Fano Resonances in a Deep-Subwavelength Spherical Hyperbolic Metamaterial Cavity

Area of Science:

• Plasmonics
• Metamaterials
• Nanophotonics

Background:

• Plasmonic whispering-gallery modes (WGMs) and sphere plasmon modes are key optical phenomena in nanostructures.
• Hyperbolic metamaterials (HMMs) offer unique electromagnetic properties due to their anisotropic permittivity.
• Fano resonances arise from the interference between a narrow resonance and a broad one, leading to asymmetric spectral profiles.

Purpose of the Study:

• To theoretically investigate multiple sharp Fano resonances in a deep-subwavelength spherical HMM cavity.
• To explore the near-field coupling between multipolar narrow plasmonic WGMs and broad-sphere plasmon modes.
• To analyze the tunability and potential applications of these Fano resonances.

Main Methods:

• Theoretical study of a spherical HMM cavity composed of alternating silver/dielectric layers around a dielectric core.
• Analysis of near-field coupling between WGMs and sphere plasmon modes.
• Calculation of far-field extinction efficiency spectra to observe Fano lineshapes.

Main Results:

• Observed multiple sharp Fano resonances with narrow linewidths (7.4–21.7 nm) due to localized electric fields.
• Demonstrated formation of symmetric, asymmetric, and typical Fano lineshapes based on coupling strength.
• Verified deep-subwavelength nature of the HMM cavity (wavelength-to-size ratio ~5.5) and tunable resonant wavelengths.

Conclusions:

• The proposed HMM cavity supports multiple narrow and tunable Fano resonances.
• The deep-subwavelength feature and controllable Fano resonances suggest potential applications in nanosensing and nanolasers.
• Near-field coupling dynamics are crucial for generating diverse Fano lineshapes.