High Peak Power Er-doped Tapered Fiber Amplifier

A novel tapered Er-doped fiber design for high peak power amplification has been developed and tested. The fiber core was based on P2O5-Al2O3-SiO2 glass matrix, which allowed simultaneous achievement of low NA and high Er content. The core diameter was changing along the fiber length from 22.5 μm (singlemode operation) to 86 μm along 2.5 meters. Amplifier based on counter propagation signal (coupled to the thin tapered fiber end) and pump (coupled into thick fiber end) was developed and a nearly diffractionlimited beam quality (M<1.27) of the output signal has been achieved. Amplification of 80 ns single frequency Gaussian-shaped pulses has resulted in peak power of 20 kW in 55 ns pulses (1.5 mJ) limited by available pump power.