Polarization‐Independent Quasibound States in the Continuum

• Published in: Advanced photonics research Vol. 3; no. 2
• Main Authors: Vaity, Pravin, Gupta, Harshvardhan, Kala, Abhinav, Dutta Gupta, S., Kivshar, Yuri S., Tuz, Vladimir R., Achanta, Venu Gopal
• Format: Journal Article
• Language: English
• Published: Hoboken John Wiley & Sons, Inc 01-02-2022; Wiley-VCH
• Subjects: bound states in the continuum; Design; dielectric metasurfaces; Glass substrates; Light; optical nanostructures; Symmetry; trapped modes
• ISSN: 2699-9293; 2699-9293
• DOI: 10.1002/adpr.202100144

A new property of the trapped mode (bound state in the continuum, BIC) supported by a dielectric resonant metasurface, which changes its lattice symmetry, is uncovered. The transformation of a metasurface composed of identical nanodisk resonators into a “diatomic” structure when one half of the nanodisks change their diameters is studied. The resulting folding of the Brillouin zone in the k‐space transforms the trapped (BIC) mode to quasi‐BIC resonances manifested in the polarization‐independent response. This novel feature is verified experimentally in the transmission of the metasurfaces illuminated by light with both linear and circular polarizations.
The excitation mechanism of a polarization‐independent trapped mode (bound state in the continuum, BIC) in dielectric metasurfaces is demonstrated. When a perturbation is introduced, the Brillouin‐zone folding occurs. This shifts the degenerate bound state at M point to the continuum at the Γ point, transforming BIC to a quasi‐BIC, where various input polarization states of light excite the same quasi‐BIC resonance.