Multi-objective optimization of dynamic VO2 metagrating: broadband polarization-independent transmission modulator

In this paper, a novel thermo-optic metagrating based on phase-change material (vanadium dioxide, VO2) is proposed for broadband, polarization-independent, and non-dispersive transmission modulation at the telecommunication wavelengths. In the pursuit of concurrent attainment of multiple performance objectives, nanostructured VO2 metagratings are optimized numerically using inverse design algorithms. Notably, adjoint optimization pertaining to both phases of VO2 facilitates better modulation capabilities within free-form shaped VO2 metagratings compared to shape-optimized methods with predetermined designs. It is verified that the free-form metagrating modulator achieves broad bandwidth (similar to 300 nm), large modulation depth (>0.8) and non-dispersive transmittance (similar to 0.2), and polarization independent operation. The design ensures polarization-independence, verified through both simulations and experiments. Experimental validation included fabricating VO2 metagratings and measuring their performance across varying temperatures. The results demonstrate agreement with theoretical predictions, highlighting the device's potential for applications in next-generation spatial light modulators, optical routers, and three-dimensional optical scanning sensors. This study underscores the promising capabilities of VO2-based metagratings in dynamic optical modulation and broadband telecommunication applications.