Nonlinear phase modulation as a broadening mechanism in a multimode erbium-doped fiber ring laser

Summary form only given. Fiber ring lasers are often oscillating on a large number of longitudinal modes. For some applications it is important to know how the number of modes depends upon the operation parameters of the laser. In this paper we show that, over a large range of values of the intracavity power, the dominant broadening mechanism is the nonlinear phase modulation. The 3-dB linewidth of a wide-band filter-tunable multimode erbium-doped fiber ring laser has been measured as a function of circulating laser power by means of an optical spectrum analyzer and a scanning Fabry-Perot interferometer. The active laser material is a 16-meter long erbium-doped fiber spliced at each end to a passive fiber loop.