Root locus method for predicting the stability of laser diodes with optical feedback

Optical feedback from an external reflector into a laser diode can render the output of the diode unstable. The critical feedback strength for a laser diode with external optical feedback is calculated using a computationally efficient root locus technique. Simulations reveal that for certain shorter feedback path lengths the critical feedback strength is elevated above the long path asymptotic value, leading to islands of increased stability.