All-dielectric metasurface based ultranarrow bandpass filter in optical C-band

Metasurface-based nanophotonics devices can potentially replace traditional bulky optical components such as optical filters, modulators, and switches. In this study, we report a dielectric metasurface-based ultranarrow bandpass filter operating at 1549.8 nm with the ability to tune the central wavelength within the C-band. The proposed tunable filter consists of a 2D periodic array of gallium arsenide blocks placed on top of a quartz substrate. The introduction of a symmetry-breaking defect results in an ultranarrow resonance with an FWHM of 0.31 nm at a 1549.8 nm wavelength when a TE-polarized wave is normally incident. The sharp, high Q factor resonance is understood to be governed by the symmetry-protected bound state in the continuum. The resonant response can be tuned by changing the periodicity, thickness, and asymmetry of the metasurface constituents. The multipolar analysis indicates the excitation of the electric quadrupole mode at the resonance wavelength. Our findings can be useful for the design of compact tunable ultranarrow bandpass filters for optical communications systems.