Polarization characteristics of the large-mode-area fiber amplifier applied in coherent combination

摘要

Built on the maser oscillator power amplifier configuration including a single mode erbium-doped fiber laser used as the signal source and a large-mode-area Erbium/Ytterbium double-clad fiber used as the gain medium, the polarization states of the signal light and the amplified signal light are experimentally investigated. The results show that the polarization degree of the output of the amplifier is low without taking any polarization control measure; after inserting a polarizer in the loop of the signal source, the degree of polarization is improved evidently and the stability of the polarization state becomes better, whether for continuous wave operation or for mode-locked operation. The mode-locked operation had a little lower polarization degree and a better PS's stability than the continuous wave operation of the output of the amplifier. When introducing a polarizer in the loop of the signal, the instability of the polarization state of the output of amplifier is mainly caused by the polarization parameter azimuth. So, the combination use of a polarizer and a polarization controller is supposed to improve the polarization degree and the stability of the output of the amplifier, furthermore, polarization-maintaining gain fiber is recommended to be used to avoid the random perturbation of the environment. This work offers an important experimental basis for the control of the PS in the laser beam coherent combination.