Bound States in the Continuum for Terahertz Metasurface Sensing

Bound States in the Continuum (BICs) represent non-radiative resonant modes embedded within the radiation spectrum, exhibiting theoretically infinite lifetimes and ultra-high quality factors. In the terahertz domain, engineered metasurfaces harness BICs to realise exceptionally sharp resonances and intense local field enhancements. By judiciously breaking symmetry or tuning coupling between modes, quasi-BICs with finite but still very high quality factors emerge, enabling highly sensitive detection of refractive-index changes, thin-film coatings and biomolecular interactions. Designs span all-dielectric arrays, metallic resonators and hybrid metal-graphene platforms, each offering pathways to modulate resonance frequency, linewidth and amplitude. Such advances promise robust, compact and label-free terahertz sensors for environmental monitoring, medical diagnostics and chemical analysis, leveraging the unique penetration and non-ionising nature of terahertz radiation.

Research from Nature Portfolio

Recent studies have demonstrated polarisation-driven control of supercavity resonances in terahertz metasurfaces. By varying the linear polarisation state at normal incidence, symmetry-protected BICs can be selectively excited or suppressed, while a strong capacitive coupling of two radiative modes gives rise to an off-Γ Friedrich–Wintgen BIC. This dual modality enables dynamic switching of high-Q resonances with polarisation angle, paving the way for reconfigurable sensors and modulators. The work further quantifies the coupling strength using an adapted Jaynes–Cummings formalism and reveals pathways to tune resonance lifetimes without altering the underlying geometry.

Bound States in the Continuum for Terahertz Metasurface Sensing publication trend

The graph below shows the total number of articles in bound states in the continuum for terahertz metasurface sensing across all publications each year (not limited to Nature Index journals).

Technical terms

Bound States in the Continuum (BIC): Non-radiative resonant modes embedded in the radiation spectrum, exhibiting theoretically infinite lifetimes and zero radiative loss.

Metasurface: Planar array of subwavelength resonators engineered to control amplitude, phase and polarization of incident waves.

Terahertz: Electromagnetic frequency band spanning approximately 0.1–10 THz, between microwave and infrared regions.

Quality factor (Q factor): Dimensionless parameter quantifying resonance sharpness, defined as the ratio of stored to dissipated energy per cycle.

Quasi-BIC: Bound state in the continuum that leaks weakly into free space due to deliberate symmetry breaking, yielding a very high but finite Q factor.

Fano resonance: Asymmetric spectral feature arising from interference between a discrete resonant state and a continuum of modes.

References

1. Ultrasensitive terahertz sensing with high-Q toroidal dipole resonance governed by bound states in the continuum in all-dielectric metasurface. Nanophotonics (2021).
2. Polarization-selective modulation of supercavity resonances originating from bound states in the continuum. Communications Physics (2020).
3. THz absorbers with an ultrahigh Q-factor empowered by the quasi-bound states in the continuum for sensing application.. Optics Express (2022).
4. All-dielectric metasurface-based multimode sensing with symmetry-protected and accidental bound states in the continuum. Results in Physics (2023).