Stability properties of dispersive extended-cavity semiconductor lasers

Summary form only given. Since semiconductor diode dispersive extended-cavity lasers are currently of interest for a variety of applications, understanding their stability properties is important to ensure stable CW laser operation. These lasers consist of a semiconductor diode coupled to some sort of external dispersive reflector (e.g. a fiber grating) that forms one mirror of the laser cavity. Quite unexpectedly, experiments have shown that for chirped fiber grating lasers (FGL), the orientation of the grating drastically alters the stability of CW operation: when the grating was placed such that the index modulation period decreased with distance from the coupled diode facet, stable single mode operation occurred, but the opposite grating orientation resulted in significant mode-hopping. This result is counter-intuitive, since the grating reflectivity spectra are identical in both cases; the only difference is in the sign of the curvature of the reflection spectrum phases, and this has been shown to play only a small role in large-scale current modulation dynamics. In this presentation, we not only explain these curious experimental results, but we also find a simple numerical prescription with which the stability of any such system can be assessed, provided the reflection spectrum of the external reflector is known.