Development of high-power Er/Yb polarization-maintaining optical amplifier for ground station uplink systems

Abstract

A high-power Er/Yb polarization-maintaining fiber amplifier is described. The amplifier operates on a single wavelength of 1546 nm and consists of a pre-amplifier with a gain up to 64 dB followed by a double-clad 25/300-m Large Mode Area (LMA) Er/Yb fiber booster stage, counter-pumped through a (2+1):1 PM combiner by two 140-W 915-nm laser diodes. The design of the amplifier required developing new splicing and re-coating approaches for the LMA PM fibers and characterizing mode-field adaptors for single-mode (SM) and LMA fibers and low-loss high-power PM pump-signal combiners maintaining a high Polarization Extinction Ratio (PER). The amplifier provides a robust diffraction-limited output of more than 50 W from true single-mode PM1550 fiber with an M 2 < 1.03 and a long-term (~200 hours) stability better than 5% in constant current mode (i.e., no power control feedback loop). With low-loss, high-quality splices between fibers with different MFDs, the maximum local fiber temperatures were kept below 60 o C. The amplifier design ensured that, even when operating at the 50-W level, the parasitic ASE in the 1-micron region was less than 2 mW. The output PER of >15 dB was limited by the quality of the pump-signal combiner which has a high probability of being improved in the future.