Abstract: The two main problems of dielectric metasurfaces for sensing based on enhanced light-matter interaction are that resonances are mainly localised inside the resonator volume and experimental Q-factors are very limited. We investigate a dielectric metasurface supporting delocalised modes based on quasi-bound states in the continuum (qBICs) to address these issues. The metasurface comprises a periodic array of silicon hollow nanocuboids patterned on a glass substrate. The resonance stems from the excitation of a symmetry-protected qBIC mode, accessed by perturbing the arrangement of the nanocuboid holes. Thanks to the variation of the unit cell with a cluster of 4 hollow nanocuboids, delocalised modes with ultra-high Q-factor are produced.

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