Ultrafast modulation of guided-mode resonance in a nonlinear silicon nitride grating

Nonlinear optical interactions in nanostructures are subjects of both fundamental research and practical applications. The optical Kerr effect, a third-order nonlinear optical phenomenon, induces anisotropic changes in the refractive index of a material under intense laser illumination. This effect is inherently weak, limiting its practical use in free-space nanophotonics. In this work, we demonstrate an enhancement of the optical Kerr effect by more than three orders of magnitude using guided-mode resonance in a dielectric diffraction grating with an overall thickness of less than 300 nm. Our study involves the design, fabrication, and measurement of the transmittance of a resonant silicon nitride crossed grating illuminated with short light pulses. We observe spectral resonance shifts with varying pulse power, leading to more than fifty percent modulation of the resonance magnitude and enabling transitions between `Off' and `On' states of transmission. We also demonstrate the capability of the grating for dynamic pulse shaping. The results presented here reveal promising directions for developing advanced all-optical devices based on free-space nanophotonics.