Topology optimization of time-transient heat conduction for thermo-optic silicon modulators

•An optimization method for design of thermo-optic silicon modulators is proposed.•To improve time-transient thermal response, topology optimization is utilized.•A detailed example for a silicon waveguide with over-clad metal heater is provided.•Faster modulator temperature rise, with reduced out-of-plane length, is achieved.•The method is broadly applicable to a range of next-generation photonic devices.