Linewidth of an optically injected semiconductor laser

This work addresses the linewidth properties of a distributed-feedback semiconductor laser submitted to optical injection. Experimentally, we first verify that under frequency-locking conditions, the slave laser has the same linewidth as the master. It can be smaller or larger than that of the free-slave laser. For lasers tuned on the same central frequency when the injected power decreases or when the master linewidth increases, we observe a partial linewidth transfer (progressive phase locking). These effects are well described theoretically by the Airy function generalized to the laser.