Optical Limiting Sensor Based on Multilayer Optimization of Ag/VO₂ Phase Change Material

An optical limiting sensor working in the infrared (IR) was developed to address the need for eye and sensor protection against laser threats. Metallic and dielectric photonic resonators (thin-film multilayers) incorporating phase-change-materials, such as vanadium dioxide (VO₂) were simulated and experimentally realized, with optimization of the deposition procedure by RF magnetron sputtering at low temperature. For the first time, the silver is placed between the substrate and the VO₂, thus improving the device limiting performances. By maximizing the difference of transmittance between the ''on'' and the ''off'' states at the standard light wavelength for telecom applications (1550 nm), we calculated optimum thickness for VO₂ and silver films. The deposited thin films were characterized by SEM and Raman spectroscopy, and VO₂ transition temperature was investigated by measuring resistance changes. As a proof of concept of the device working principle, we calculated transmittance drop of 70% when the sensor is exposed to a laser pulse excitation (20 ps, 500 MW/cm²). Our results pave the way for multilayer with optical limiting properties.