Stable operation range for laser diodes with an integrated passive cavity in the presence of external optical feedback

Abstract

It is shown that a laser diode with an integrated passive cavity yields higher tolerable levels of feedback from distant reflections than an equivalent long solitary laser diode. To ensure this high tolerance for external feedback, the internal feedback level in the integrated passive cavity must be of the order of about 10%. Then the laser diode remains stable up to external feedback levels in excess of 1% even if the internal reflection phase is not carefully adjusted. External reflections from a cleaved fiber end are then not sufficient to drive the laser into coherence collapse, if realistic coupling efficiencies between laser diode and fiber are taken into account. The low feedback sensitivity is explained by the combination of the long effective length of the laser and a high relaxation resonance frequency. Therefore, quantum-well laser diodes with a long length and a high relaxation resonance frequency are likewise expected to exhibit low feedback sensitivity. >