Relaxation of the single-mode emission conditions in extended-cavity semiconductor lasers with a self-organizing photorefractive filter

Abstract

Commercial 1.55-microm extended-cavity semiconductor lasers provide single-mode operation that can be continuously tuned over a range larger than 100 nm without mode hopping. But such performance requires delicate factory adjustment and high mechanical stability of the external cavity. Furthermore, at high emission power the tuning range is limited to small values because of the annoying multimode operations that sometimes occur. We have shown that the alignment constraints can be relaxed by use of an intracavity photorefractive filter. Here we present new results obtained with a crystal with low absorption and high photorefractive gain. We demonstrate that, without inducing excessive additional loss, we can preserve single-mode emission at an output power higher than the maximum power obtained in the absence of a photorefractive crystal over the full tuning range of the laser.

Self-induced transverse mode selection in a photorefractive extended cavity laser diode

“…This extends the operating range over which this extended cavity is single mode. Although our numerical analysis has only been done on the transverse mode structure, note that the photorefractive crystal with the distant mirror also acts as a frequency self-adapted filter, like in [5][6][7][8]. We have experimentally demonstrated this self-adapted filter to also make a selection on the axial modes that lead to a single transverse and axial oscillation of this extended cavity BAL diode with a single-mode emission up to 33.7 mW.…”

“…All the reported cavities [4][5][6][7][8] support a unique transverse modal structure and the selforganizing process only occurs on the axial modes. Now we are interested in studying whether a similar process can act on the transverse modal structure of a laser.…”

“…In a distant mirror based extended cavity around 810 nm, the insertion of a photorefractive Barium Titanate (BaTiO 3 ) crystal leads to a single axial mode operation over a wide injected current range without any other frequency filter [7]. Whereas the use of an intracavity photorefractive crystal in a tunable extended cavity relaxes the distant grating alignment constraints to avoid mode hopping [8].…”