Measurements which demonstrate the strong dependence of the linewidth-broadening factor α on photon energy in 1.5 μm lasers are reported, α was found to vary between 3 and 11 over a 40 meV energy range. The consequences for the linewidth and transient wavelength chirping in 1.5 μm DFB lasers, where the operating wavelength may be different from the peak gain wavelength, are examined.