Extreme Narrowing of the Distributed Feedback Fiber Laser Linewidth Due to the Rayleigh Backscattering in a Single-Mode Fiber: Model and Experimental Test

Abstract

We present our theoretical model and experimental results on the extreme linewidth narrowing of an erbium-doped fiber distributed feedback (DFB) laser due to an additional random DFB via Rayleigh backscattering in a long single-mode fiber connected to the laser. The relative narrowing of instantaneous (<1 μs) linewidth in such a hybrid cavity configuration predicted by the theoretical model may exceed six orders of magnitude, whereas the linewidth estimated from the phase noise measurements narrows by four orders of magnitude from 15 Hz to 10–3 Hz in the hybrid configuration, with the lower limit defined by the background electrical noise. Significant narrowing was also observed for the long-term ≥10 μs) linewidth directly measured by the self-delay heterodyne technique: the values for the DFB laser and hybrid configuration amount to 6 kHz and 160 Hz, respectively.