Quantifying Optical Feedback Into Semiconductor Lasers via Thermal Profiling

We show that thermal profiling can be used to monitor optical feedback into semiconductor lasers in photonic integrated circuits, where direct optical access is impractical. The optical output power of a laser, both free-running and when exposed to optical feedback, can be quantitatively determined from thermal measurements alone, without recourse to direct optical measurements. Furthermore, the shift in threshold current resulting from optical feedback can be determined from the thermal measurements, enabling quantitative determination of the feedback coupling efficiency into the laser.