High-frequency oscillations and self-mode locking in short external-cavity laser diodes

An effect of compound-cavity mode competition for a laser diode with a short external cavity is investigated analytically and numerically on the basis of a round-trip approximation for emitted photons in the external cavity. Due to the noncoincidence of the compound-cavity modes with possible frequencies of stationary lasing, such competition may cause self-locking of two compound-cavity modes with deep high-frequency oscillations of the laser output for a short (typically ⩽5 mm) external cavity. Simple analytical expressions for critical feedback parameters and the frequencies of self-oscillations are given, as well as a generalized diagram of different dynamic regimes of a short external-cavity laser, which shows these regimes of high-frequency self-oscillations as well as coherence collapse instability. The results may be considered a guideline for the design of high-speed laser diodes with an integrated passive cavity. In particular, such a device may be a very efficient pulse source in the microwave (>20 GHz) region