Entraining power-dropout events in an external-cavity semiconductor laser using weak modulation of the injection current

We measure experimentally the effects of injection current modulation on th e statistical distribution of time intervals between power-dropout events o ccuring in an external-cavity semiconductor laser operating in the low-freq uency fluctuation regime. These statistical distributions are sensitive ind icators of the presence of pump current modulation, Under most circumstance s, me find that weak low-frequency (in the vicinity of 19 MHz) modulation o f the current causes the dropouts to occur preferentially at intervals that are integral multiples of the modulation period. The dropout events can be entrained by the periodic perturbations when the modulation amplitude is l arge (peak-to-peak amplitude greater than or equal to 8% of the de injectio n current). We conjecture that modulation induces a dropout when the modula tion frequency is equal to the difference in frequency between a mode of th e extended cavity laser and its adjacent antimode, We also find that the st atistical distribution of the dropout events is unaffected by the periodic perturbations when the modulation frequency is equal to the free spectral r ange of the external cavity, Numerical simulations of the extended-cavity l aser display qualitatively similar behavior, The relationship of these phen omena to stochastic resonance is discussed and a possible use of the modula ted laser dynamics for chaos communication is described.