Dynamic Modeling of PID Temperature Controller in a Tunable Laser Module and Wavelength Transients of the Controlled Laser

Temperature controllers based on proportion-integration-differentiation (PID) control strategy are widely used in tunable semiconductor laser modules for optical communication systems. A properly designed temperature controller (consisting of a thermoelectric cooler, a thermistor, and control circuits) can maintain a nearly constant laser temperature regardless of the variation of environment temperature (
${-}{\rm 20}^{\circ}{\rm C}$
to 70
$^{\circ}{\rm C}$
). However, it cannot avoid the thermal transients arising from fast changes of tuning-section currents in fast wavelength-switching applications. In these cases, the behavior of the thermal transients in the laser is closely related to characteristics of the temperature controller. In this paper, a dynamic 3-D thermal model of a packaged sampled grating distributed Bragg reflector (SG-DBR) laser module containing a PID temperature controller is presented. This model is based on finite element method. It can simulate the dynamic working process of the temperature controller when the laser is wavelength-switched by current change and the corresponding transient temperature in the laser chip. Transient temperature variations and wavelength drifts of the SG-DBR laser after switching for different PID coefficients are simulated and discussed. Wavelength stabilization times and their influences on the laser's actual application in dynamic optical networks are also discussed.