The design of optical communication systems involves many challenges. Design objectives like thermal management, miniaturization, and improving bandwidth and signal integrity often conflict, and empirical design methods are costly. Thanks to multiphysics simulation, engineers and scientists can understand, predict, and optimize photonic systems to build more powerful and efficient products, faster. The COMSOL Multiphysics® software is a unique, integrated simulation environment for wave optics, ray optics, heat transfer, MEMS, and other physics. It empowers engineers to model optical fibers, waveguides, couplers, nonlinear optics, gratings, and metamaterials — allowing for high-fidelity structural-thermal-optical performance (STOP) analysis, multiscale modeling, optimization, and uncertainty quantification.