Design of a large-mode-area tapered fiber amplifier for amplification of ultrashort laser pulses at 1535 nm wavelength

Abstract

We design a W-type large-mode-area erbium doped tapered fiber with effective mode area varying from 1770 µm2 to 840 µm2with tolerance ± 0.0005 in refractive indices of different layers of fiber. The beam quality of the pulses is ensured by effective single-mode operation. We investigate the amplification of high power femtosecond pulses in this fiber by using nonlinear Schrodinger equation including gain term. It is solved using split-step Fourier method for both up-tapered (effective mode area increasing along the length) and down tapered (effective mode area decreasing along the length) fiber configurations at centered around 1535 nm wavelength. In both configurations of fiber, input pulse parameters like peak power, pulse width, and fiber length are calculated for maximum amplification with the least amount of pulse shape distortion. In down-tapered configuration, we numerically demonstrate the amplification of 1 kW peak power, 560 fs duration pulse to 3.6 MW peak power, 12 fs amplified pulse. In up-tapered configuration, we obtain the amplification of 2 kW, 565 fs input pulse to ∼7.9 MW peak power, ∼11 fs pulse. The fiber is useful for amplifying high-power laser pulses, and the resulting pulses can be used for laser processing, spectroscopy, and remote sensing.