Comments on “Optical spectra of a semiconductor laser with incoherent optical feedback“

The author thanks J. S. Cohen et al.(see ibid vol. 26, p. 982-90, 1990) for their contribution to the literature on incoherent feedback to semiconductor laser diodes. He takes issue with the assertion therein that fully incoherent feedback to the laser diode has been produced. This is because of the presence of external-cavity modes around the laser´s main mode that are induced by the feedback mirror. The Wiener-Khinchine theorem states that the normalized power-spectral-density function and the normalized autocoherence function form a Fourier transform pair. An application of this theorem to an idealized single-mode laser line upon which are superposed external-cavity modes is shown