Abstract: The invention relates to a broadband light source including an amplifying guide structure (1). The light source includes a device (45) of exciting the guide structure (1). The stimulated guide structure (1) emits light (7, 8) that accepts strong spatial coherence and weak time coherence. The light (7) is transmitted forwards (2) having a spontaneous emission spectrum. The light source also includes a rear mirror (5), reflecting only for a narrower range of wavelengths than the spontaneous emission spectrum and produces emission (E) forwards (2) with an emission spectrum controlled around an average wavelength. The rear mirror is inserted between the excitation means and the guide structure.