OPTICAL FEEDBACK-INDUCED NOISE IN PIGTAILED LASER DIODE MODULES

The sensitivity of commercially available pigtailed laser diode modules to optical feedback, in terms of laser relative intensity noise, is investigated. A pigtailed laser diode model which is based on multimode rate equations, Langevin operators, and optical feedback terms is used to predict that operation in the "coherence collapse" region can be avoided in high speed, short haul, optical data links by trading off optical launch power into the pigtail with decreased laser/fiber coupling efficiency. Experimental results for three pigtailed laser diode modules indicate that with a laser/fiber coupling efficiency of 4%, an external feedback level of between -15 and -17 dB can be tolerated before the laser enters the "coherence collapse" region. Good correlation between these results and predictions from the numerical model are obtained.