Effect of solvent absorption on the optical properties of 3D printed methacrylate waveguide

Abstract

Methacrylate-based photopolymer waveguides are 3D printed using stereolithography as a single-step fabrication technique and the light propagation through these waveguides is investigated in the presence of various solvents. Solvent absorption on the photopolymer surface is found to play a significant role in the optical output power of the waveguide. Swelling of the photopolymer caused by the solvent absorption is found to increase the optical power transmission through the waveguide. Mixing isopropanol and glycerol with DI water separately at specific concentrations so that their respective refractive indices remain similar, it is observed that isopropanol samples increase the optical power by ~36% compared to glycerol samples, which showed optical power enhancement around 4.9%. A first-order optical model is presented that shows the increase in optical power has a spontaneous response due to the change in the refractive index of the waveguide surface upon solvent contact, followed by a dynamic response due to the formation of the swelling layer as the absorbed solvent diffuse inside the polymer. The methacrylate-based waveguide also showed selectivity towards different concentrations of isopropanol. Results from our study show that the optical properties of the given methacrylate-based photopolymer are largely affected by the absorption affinity of the solvent towards the photopolymer rather than the solvent’s refractive index, which can be crucial for designing integrated optical devices using methacrylate-based photopolymers that work in a different solvent condition.