buffer layer 3 for encouraging the growth of subsequent layers an active layer 4 of a semiconductor alloy based on inp or gaas intended to amplify light and possibly incorporating quantum wells another semiconductor layer 5 referred to as a protection layer having a thickness of the order of 0 1 u03bcm an n type doped confinement layer 6 according to the invention of a semiconductor alloy based on inp or gaas whose thickness varies longitudinally from approximately 0 5 u03bcm to approximately 1 u03bcm a semiconductor layer 7 referred to as the contact layer which is strongly p type doped and contributes to correct injection of an electric current and the confinement layer 6 contains zinc electron acceptors a and a lower concentration of silicon electron donors d the p type doping concentration n p corresponds to the difference between the concentration of acceptors a and the concentration of donors d 0050 fig3 shows a curve 11 representing the p type doping concentration profile n p of the confinement layer 6 as a function of the length l of the tapered optical guide g along the propagation axis z the concentration n p is substantially constant in the region r 1 and therefore over the whole of the length l 1 it is typically equal to approximately 7 u00d7 10 17 cm u2212 3 the concentration n p decreases substantially linearly in the region r 2 and therefore.