Polarization-selective modulation of supercavity resonances originating from bound states in the continuum

Chan Kyaw,Eddie C Red,Mikkel A Thomas,Wesley Sims,Riad Yahiaoui,Willie S Rockward,Viet Tran,Thomas A Searles,Kyron Keelen,Andrew Sarangan,Imad Agha,Joshua A Burrow

doi:10.1038/s42005-020-00453-8

Abstract

Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Primarily, the formation of BICs in periodic photonic band gap structures are driven by symmetry incompatibility; structural manipulation or variation of incidence angle from incoming light. In this work, we report two modalities for driving the formation of BICs in terahertz metasurfaces. At normal incidence, we experimentally confirm polarization driven symmetry-protected BICs by the variation of the linear polarization state of light. In addition, we demonstrate through strong coupling of two radiative modes the formation of capacitively-driven Freidrich-Wintgen BICs, exotic modes which occur in off-Γ points not accessible by symmetry-protected BICs. The capacitance-mediated strong coupling at 0° polarization is verified to have a normalized coupling strength ratio of 4.17% obtained by the Jaynes-Cummings model. Furthermore, when the polarization angle is varied from 0° to 90° (0° ≤ ϕ < 90°), the Freidrich-Wintgen BIC is modulated until it is completely switched off at 90°.

Highlights

Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics
Α has been defined as 100% × δi/δmax where δi is the distance between the gap center and the symmetry line and δmax is 72.5 μm
The degree of asymmetry before quasi-BICs can be detected is larger for x-polarization where the transmission dip only becomes visible in simulations around 11% as compared to 3% asymmetry for y-polarization

Summary

Introduction

Bound states in the continuum (BICs) are widely studied for their ability to confine light, produce sharp resonances for sensing applications and serve as avenues for lasing action with topological characteristics. Unlike SP-BICs, FW-BICs are observed at off-Γ points in regions with an accidental symmetry These regions of the band dispersion result in extremely high Q factors around the FW-BIC, called near-BIC25 or supercavity resonances[13,26], and are attributed to the coupling strength of the two radiative modes that interfere destructively. Recent investigations by Han et al.[26] reported resonance-trapped BICs with similar mechanism as FW-BICs for THz metasurfaces by tailoring the geometric lengths of the silicon resonators. They reported frequency and Q-factor modulation of the supercavity resonance through optical pumping of the silicon resonators. Pankin et al.[34] reported FW-

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Conclusion