Spectral behavior of directly modulated laser diodes exposed to Rayleigh backscatter from a single-mode fiber

The spectral behavior of a laser diode exposed to Rayleigh backscattering (RB) from a single-mode fiber is investigated for arbitrary laser-fiber coupling efficiency, fiber length, and coherence time of the light of the free-running source. It is found that resonance effects in the spectral behavior of laser diodes exposed to RB from a single-mode fiber occur only for coupling efficiencies above a critical value eta /sub c/. This threshold is very low for unmodulated light but it is substantially increased when the light is modulated. A simple mathematical relation is given showing the dependence of the threshold on the fiber length and on the coherence time of the light.<>