[Paper Review] Hybrid bound states in the continuum in terahertz metasurfaces

Junxing Fan, Zhanqiang Xue+6 more|arXiv (Cornell University)|Mar 22, 2023

Metamaterials and Metasurfaces Applications9 citations

TL;DR

The paper introduces hybrid bound states in the continuum (BICs) in terahertz metasurfaces to reduce scattering losses and enhance radiative quality factors, achieving a radiative Q boost factor over 14.6 in the hybrid lattice and revealing multiple Fano resonances via Brillouin-zone mode transfer.

ABSTRACT

Bound states in the continuum (BICs) have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics, biosensors, and ultrafast optical switches. The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor (Q) and asymmetry. Here, we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice.We observe significant increase of radiative Q in the hybrid lattice compared to uniform lattice with a factor larger than 14.6. In the hybrid BIC lattice, modes are transferred to Gamma point inherited from high symmetric X, Y and M points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing. This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.

Motivation & Objective

• Motivate the use of bound states in the continuum (BICs) for enhanced light–matter interaction in photonics.
• Propose a lattice engineering approach to reduce radiation density and increase robustness of symmetry-protected BICs.
• Show that hybrid BIC lattices yield higher radiative Q factors than uniform lattices in terahertz metasurfaces.
• Demonstrate mode transfer to the Gamma point from X, Y, and M points and identify multiple Fano resonances in the far field.

Proposed method

• Introduce a hybrid lattice design to couple and suppress radiation losses in terahertz metasurfaces.
• Analyze radiation density and quality factor (Q) enhancements for hybrid versus uniform lattices.
• Observe mode transfer to the Gamma point from high-symmetry Brillouin-zone points (X, Y, M) enabling multiple Fano resonances in the far field.
• Characterize far-field spectral features corresponding to the transferred modes and Fano resonances.

Experimental results

Research questions

• RQ1 Can a hybrid lattice design reduce scattering losses of BICs in terahertz metasurfaces compared to a uniform lattice?
• RQ2 How does the radiation density and radiative Q factor change when transferring modes to the Gamma point from X, Y, and M points?
• RQ3 Do the transferred modes manifest as multiple Fano resonances in the far field, and can this enable hyperspectral sensing?

Key findings

• Radiative Q in the hybrid lattice increases by a factor larger than 14.6 compared to the uniform lattice.
• Modes are transferred to the Gamma point inherited from high symmetric X, Y and M points in the Brillouin zone.
• The transferred modes reveal as multiple Fano resonances in the far field.
• The hybrid lattice reduces scattering losses and enhances robustness of symmetry-protected BICs through lattice engineering.
• The approach suggests a generalized path toward improving BIC robustness in photonics and optoelectronics devices.