Injected carrier effects on modal properties of 1.55 mu m GaInAsP lasers

The authors report the observation of a strong variation of the active layer refractive index with the current in a 1.55 mu m "gain-guiding" GaInAsP laser 12 mu m wide. A negative refractive index change of several 10 super(-2) has been found between the center and the edge of the stripe from a transverse mode distribution analysis and a study of the wavelength shift of the longitudinal modes with the current. The authors have shown that this effect can explain the increase of threshold current of a gain-guiding laser for a small stripe width. They have observed, moreover, a time dependence of the transverse mode width in the transient regime in pulsed operation and a broadening of a time average spectrum of a stabilized single longitudinal mode laser under current modulation. They have also shown that these two last effects can be explained by the refraction index current dependence.