Fourier-component engineering to control light diffraction beyond subwavelength limit

Resonant physical phenomena in planar photonic lattices, such as bound states in the continuum(BICs) and Fano resonances with 100% diffraction efficiency, have garnered significant scientific interest in recent years owing to their great ability to manipulate electromagnetic waves. In conventional diffraction theory, a subwavelength period is considered a prerequisite to achieving the highly efficient resonant physical phenomena. Indeed, mostof the previous studies, that treat anomalous resonance effects, utilize quasiguided Bloch modes at the second stop bands open in the subwavelength region. Higher (beyond the second) stop bands open beyond the subwavelength limit have attracted little attention thus far. In principle, resonant diffraction phenomena are governed by the super-position of scattering processes, owing to higher Fourier harmonic components of periodic modulations in lattice parameters. But only some of Fourier components are dominant at band edges with Bragg conditions. Here, we present new principles of light diffraction, that enable identification of the dominant Fourier components causing multiple diffraction orders at the higher stopbands, and show that unwanted diffraction orders can be suppressed by engineering the dominant Fourier components. Based on the new diffraction principles, novel Fourier-component-engineered (FCE) metasurfaces are introduced and analyzed. It is demonstrated that these FCE meta surfaces with appropriately engineered spatial dielectric functions can exhibit BICs and highly efficient Fano resonances even beyond the subwavelength limit.

Automated summary

The study introduces new principles of light diffraction in planar photonic lattices, showing how multiple diffraction orders at higher stopbands are caused by dominant Fourier components which can be engineered to suppress unwanted diffraction orders. The novel Fourier-component-engineered (FCE) metasurfaces exhibit bound states in the continuum (BICs) and highly efficient Fano resonances even beyond the subwavelength limit, demonstrating the potential for manipulating electromagnetic waves effectively.