INSTABILITY IN SELF-PULSATION IN LASER-DIODES AND ITS EFFECT ON ALL-OPTICAL SYNCHRONIZATION

The effect of short- and long-term frequency instability in self-pulsa tion on all-optical synchronization using a twin-section laser diode i s experimentally investigated. Short-term frequency instability broade ns the unlocked full width at half maximum (FWHM) of the fundamental o f the rf spectrum of the self-pulsating laser diode. We show experimen tally that the value of the unlocked FWHM, and thus the level of short -term instability, has a direct effect on the optical power required t o maintain synchronization. A novel means of reducing the FWHM is pres ented, based on a reflective transmission line stub connected to the a bsorber of the twin-section self-pulsating laser diode in use. A reduc tion of up to 5 dB in the average optical power required for effective synchronization is observed. Long-term frequency instability can prev ent synchronization from taking place because of the limited lock-in f requency range of a self-pulsating laser diode. It is shown that for t he devices used here, the dominant cause of long-term instability is t emperature. A new method of sensing the temperature in a twin-section laser, called absorber current temperature sensing, which reduces the measured unsycnchronized frequency drift by more than 5:1, is demonstr ated. The results have important implications for the design of new al l-optical synchronization subsystems, based on self-pulsating laser di odes.