Self-frequency-shifted solitons in a polarization-maintaining, very-large-mode area, Er-doped fiber amplifier

We demonstrate soliton self-frequency-shifted, femtosecond-pulse amplification in a newly-developed, polarization-maintaining, Er-doped, very-large-mode-area fiber amplifier. The PM-VLMA Er fiber had a core diameter of 50 μm, an effective area of ~1050 μm², and Er absorption of 50 dB/m. The measured birefringence beat length of the PM-VLMA Er fiber was 14.1 mm. The soliton wavelength could be shifted by more than 90 nm. The soliton generation process resulted in remarkably clean, 86 fs pulses with 21 nJ energy at 1650 nm and 244 kW peak power from an all-fiber, fusion spliced system without bulk-optics for pulse compression. The polarization extinction ratio of the soliton was greater than 40 dB, and the M² was 1.1. The fully polarization-maintaining fiber laser system provides robust and stable soliton generation. Peak-to-peak variation in the soliton wavelength, measured over the course of an hour was only 0.03% and pulse energy variation was only 0.5%.