Group-velocity dispersion analysis of large mode-area doped fibers implemented in a laser cavity during operation

Abstract

Developments in the field of high-power fiber lasers require extensive knowledge of the fiber structure parameters in various operating states. In an effort to gather such knowledge, this paper presents the results of dispersion characterization measurements using ytterbium-doped large mode area double-clad fibers implemented in the cavity of a high power fiber laser during operation. The laser cavity is built into one arm of a Mach-Zehnder interferometer. Using dichroic mirrors the radiation of a supercontinuum light source is coupled into the fiber sample. Various types of large mode-area fibers were examined under different operating conditions of the laser setup. Group-velocity dispersion characteristics of two large mode-area double-clad fiber amplifiers with various launching laser power levels were analyzed. The dispersion parameters for different fiber designs and various doping levels are investigated over a broad spectral range of about 1.3 μm. The experiment utilizes a supercontinuum source developed within this laboratory, as well as a Mach-Zehnder interferometer with a dual-channel spectral-detection system sensitive to wavelengths from 0.4 μm to 1.7 μm. Temporally resolved spectrograms recorded at distinct delay positions enable the detection of interference fringes for the equalization-wavelength. By applying a Sellmeier polynomial fit to the wavelength dependent differential group-delay function, the group-velocity dispersion has been derived.