Hydrogels for active photonics

Conventional photonic devices exhibit static optical properties that are design-dependent,including the material’s refractive index and geometrical parameters.However,they still possess attractive optical responses for applications and are already exploited in devices across various fields.Hydrogel photonics has emerged as a promising solution in the field of active photonics by providing primarily deformable geometric parameters in response to external stimuli.Over the past few years,various studies have been undertaken to attain stimuli-responsive photonic devices with tunable optical properties.Herein,we focus on the recent advancements in hydrogel-based photonics and micro/nanofabrication techniques for hydrogels.In particular,fabrication techniques for hydrogel photonic devices are categorized into film growth,photolithography(PL),electron-beam lithography(EBL),and nanoimprint lithography(NIL).Furthermore,we provide insights into future directions and prospects for deformable hydrogel photonics,along with their potential practical applications.