THE SYMMETRY OF THE AMPLIFIED SPONTANEOUS EMISSION-SPECTRUM IN COMPLEX-COUPLED DFB LASERS

We present relations between facet reflections and coupling coefficien t for the amplified spontaneous emission (ASE) spectrum of a complex-c oupled, an index-coupled and a gain-coupled distributed feedback (DFB) laser to have a mirror image with respect to the Bragg wavelength. We show that the ASE spectrum of a complex-coupled DFB laser cannot be s ymmetric in general with respect to the Bragg wavelength. The index-co upled and gain-coupled DFB lasers can have symmetric ASE spectrum for some values of the phase of the facet reflection coefficient that are determined.