Canceling Thermal Cross-Talk Effects in Photonic Integrated Circuits

Thermal actuators are among the most consolidated and widespread devices for the active control of photonic integrated circuits (PICs). As a main drawback, mutual thermal crosstalk among actuated devices integrated onto the same photonic chip can affect the working point of the PIC and can reduce the efficiency of automated tuning and calibration procedures. In this paper, a strategy to cancel out the effects of the phase coupling induced by thermal crosstalk is presented. In our technique, we named thermal eigenmode decomposition (TED), all the actuators of the PIC are controlled simultaneously according to the eigensolution of the thermally coupled system. The effectiveness of the TED method is validated by numerical simulations and experiments carried out on coupled microring resonator and switch fabrics of Mach-Zehnder interferometers. With respect to individual control of phase actuators, where thermal crosstalk can hinder the convergence of automated tuning algorithms, with the TED technique convergence is always reached, requires a lower number of iterations, and is less sensitive to the initial state of the PIC. The proposed TED method can he applied to generic tuning and locking algorithm, can be employed in arbitrary PIC architectures and its validity can be extended to systems where phase coupling is induced by other physical effects, such as mutual mechanical stress and electromagnetic coupling among RF lines.