Spectral width optimization in random DFB fiber laser

Abstract

Summary form only given. Lasers with random distributed feedback (DFB) owing to Rayleigh scattering in optical fibers [1] have attracted a great interest: a number of papers demonstrating new laser schemes and applications have been proposed [2-7] recently. Moreover, the generation output power and, more generally, generation power distribution could be described both analytically and numerically within simple balance models [8-9]. However, spectral properties of random DFB fiber lasers are not studied except some attempt made in [10]. Generation spectrum of random DFB fiber laser is quite broad (more than 1 nm), and physical mechanisms of its formation and broadening are still unclear. There is no any practical solution up to date to minimize the generation spectrum width. Here we experimentally show the way to minimize the generation spectral width.We use the one-arm laser scheme having a single pump from a one fiber facet. Such design does not include any elements except the fiber and the pump source. We use polarized ytterbium doped fiber laser generating up to 10 W at 1064 nm and telecommunication TrueWave fiber of different length varying from 2 km to 15 km. The laser generates Stokes wave at 1118 nm in the backward direction. An increase of the fiber length results in decreasing of the laser generation threshold pump power while preserving the slope efficiency almost constant, Fig 1a. At the same time, spectral width is also changed. Namely, the longer laser, the narrower the generation spectrum (at the fixed generation power), Fig. 1b. However, increasing the length over the 13 km does not affect the spectrum width. If one fixes the pump power, the spectral width remains the same for any cavity length revealing universal linear spectral broadening law, Fig. 1c. Such behaviour may indicate that the generation spectrum width is mostly determined by cross-phase modulation with the pump wave.