FM-to-AM modulations are harmful to output characteristics of large-scale laser facility. In SG-III laser facility, some key techniques have been employed to suppress FM-to-AM modulations. Firstly, phase modulator was arranged at the end of fiber laser injection system to avoid GVD and PMD in the SM fiber system. Secondly, a fiber-based polarization rotated filter was proposed to suppress FM-to-AM modulations independently on each beam. Finally, less wave plates were employed and liquid crystal modulators were coated for decreasing weak etalon effect in preamplifier system. The results indicated that it can reduce the modulation depth less than 10% at a modulation frequency of 2.488GHz in SG-III laser facility.

Polarization maintaining fiber amplifier using ytterbium doped single mode fiber (SMF) is pro posed. A 45° Faraday rotator mirror (FRM) and a polarization independent fiber loop circulator (FLC) with polarization maintaining fiber (PMF) pigtails are used to realize double pass amplification and birefringence self compensation. Arbitrary state of polarization (SOP) such as the linear polarization and elliptical polar ization can be maintained. Polarization maintaining amplification of phase modulated pulse with this ampli fier is experimentally demonstrated while introducing little intensity modulation itself.