Observation of period doubling, period tripling, and period quadrupling in a directly modulated 1.55 μm InGaAsP distributed feedback laser diode

Dynamic characteristics of a directly modulated 1.55 μm InGaAsP distributed feedback semiconductor laser are investigated up to a modulation index of 12. Period doubling, period tripling, and period quadrupling are observed for the first time. The irregular behavior is examined at various bias current levels and modulation frequencies. The route to chaos is found to be via period doubling followed by period quadrupling and period tripling. The observed irregular behavior is attributed to the relatively small fraction of the spontaneous emission coupled into the lasing mode (β factor) of distributed feedback lasers, which is confirmed by a separate experiment.