Nonlinear dynamics of a directly modulated 1.55 mu m InGaAsP distributed feedback semiconductor laser

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Abstract
Dynamic characteristics of a directly modulated 1.55- mu m InGaAsP distributed-feedback (DFB) semiconductor laser are investigated up to a modulation index of 12. Period doubling, period tripling, period quadrupling, and chaos are observed for the first time. The irregular behavior is examined at various bias current levels and modulation frequencies, and it is found that a possible route to chaos in modulated semiconductor lasers is via period doubling followed by period quadrupling and period tripling. This is attributed to the relatively smaller fraction of the spontaneous emission coupled into the lasing mode, i.e., beta factor, of the DFB lasers. This speculation is supported by an experimental measurement of the beta factor, which is found to be ten times smaller than that for a Fabry-Perot laser, and further confirmed by a rate equation simulation using the measured beta factor.