2 kW single-mode fiber laser with 20-m long delivery fiber and high SRS suppression

Abstract

A 2 kw single-mode fiber laser with a 20-m long delivery fiber and high back reflection resistance has been demonstrated. An Yb-doped fiber with large core size and differential modal gain is used to realize high SRS suppression and single-mode operation simultaneously. The 20 m-long delivery fiber gives flexibility to the design of processing systems. An output power of 2 kW is achieved at a pump power of 2.86 kW. The slope efficiency is 70%. The power of the Stokes light is less than -50 dB below the laser power at the output power of 2 kW even with a 20-m delivery fiber. Nearly diffraction-limited beam quality is also confirmed (M2 = 1.2). An output power of 3 kW is believed to be achieved by increasing pumping power. The back reflection resistance properties of the fabricated singlemode fiber laser is evaluated numerically by the SRS gain calculated from measured laser output spectra and fiber characteristics. The acceptable power of the back reflection light into the fiber core is estimated to be 500 W which is high enough for processing of highly reflective materials. The output power fluctuation caused by SRS and back reflection in materials processing will be well suppressed. Our high power single-mode fiber lasers can provide high quality and stable processing of highly reflective materials.