Abstract
We investigate the nonlinear dynamics of a pulse injected semiconductor laser that a laser is optically injected by repetitive pulses. Rich dynamics, including both oscillation and pulsation states, are found by varying the intensity and repetition rate of the injection pulses. The laser enters into chaotic pulsation (CP) and chaotic oscillation (CO) states through individual period-double routes. Under proper injection, frequency-locked states with different winding numbers, the ratio of the oscillation relaxation frequency and the repetition frequency of the injection pulses, are observed. The winding numbers reveal a Devil's staircase structure, where a Farey tree showing the relation between the neighboring states is presented. Moreover, the bandwidth enhancement phenomenon of the chaotic states under repetitive pulse injection is also discussed.