OPTICAL-FEEDBACK-INDUCED CHAOS AND ITS CONTROL IN MULTIMODE SEMICONDUCTOR-LASERS

The effects of optical feedback in multilongitudinal mode semiconducto r lasers are studied through computer simulations. Two separate regime s are found based on the length of the external cavity. For long exter nal cavities (external-cavity mode spacing larger than the relaxation- oscillation frequency), the laser follows a quasi-periodic route to ch aos as feedback is increased. For short external cavities, the laser c an undergo both quasi-periodic and period doubling routes to chaos. Wh en the laser output becomes chaotic, the relative-intensity noise is g reatly increased (by more than 20 dB) from its solitary-laser value. C onsiderable attention is paid to the effects of optical feedback on th e longitudinal-mode spectrum. The stabilization of the mode spectrum a nd the reduction of the feedback-induced noise through current modulat ion are studied and compared with experimental results. Current modula tion eliminates feedback-induced chaos when the modulation frequency a nd depth are suitably optimized. This technique of chaos control has a pplications in optical data recording.