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 (∼300 nm), large modulation depth (>0.8) and non-dispersive transmittance (∼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.