Estimation of maximum temperature and thermal crosstalk between two active elements in a PIC: development of a thermal equivalent circuit

The operating temperature plays a key role in the performance and lifetime of photonic integrated circuits (PICs). Miniaturization and increasing heat dissipation promote thermal crosstalk effects and pose additional challenges to the PIC designer. The European Photonics Industry Consortium recommends thermal modeling during design phase. However, a fully numerical optimization of a particular layout requires an unrealistically large number of simulations. Here, we propose a compromise approach: a set of carefully chosen simulations are performed with a multi-physics software. The obtained results are used to derive a linearized equivalent thermal circuit that can be used to maximize the power levels and to minimize the distance between the chosen components while guaranteeing the absence of a thermal crosstalk. For simplification, this model is derived considering a PIC with only two active components. Other parameters are varied, such as the material of the holder (silicon or diamond) and the layer of epoxy that is used to attach the PIC to the holder. The obtained circuit is used to determine the maximum dissipated power or the minimum distance between the components while keeping some predetermined specifications. The model can be extended to contain more elements or to include transient analysis of the temperature distribution.