Thermal simulation and structure design of thermally tuned multi-channel interference (MCI) laser

Thermally tuned multi-channel interference (MCI) lasers are really advantageous for applications of coherent optical communication systems, in which light sources with narrow linewidth are critical requirements. To optimize the thermally tuned MCI lasers, simulations of thermal effects are quite important. In this paper, we analyze the thermal tuning efficiency of such lasers using the finite element analysis software Comsol. First, the effect of the air insulation thickness on the thermal tuning efficiency is simulated and we found that the thicker air insulation the larger phase shift. Then, influences of different microheater lengths on the temperature distribution of waveguide core are analyzed in detail. Simulation results indicate that the waveguide core temperature is increasing with the microheater length. In addition, considering the lasing wavelength depends on the temperature change of InP, the curve of phase shift versus thermal tuning power is obtained. It is predicted that the microheater power of πphase shift is about 5.4 mW for a 100 μm-long suspended thermal tuning waveguide. Finally, for the verification of our simulations, some test structures of the suspended thermal tuning waveguide with the air insulation are experimentally fabricate. By measuring the phase of the output light under different thermal power, about 5.7 mW microheater power is needed for π-phase shift of the 100 μmlong suspended thermal tuning waveguide, which is consistent with the simulation result. It can be concluded that the thermal simulations and structure designs will be beneficial for the realization of the thermally tuned MCI lasers in the future.