Measurement of resonant and nonresonant induced refractive index changes in Yb-doped fiber grating amplifier

Experimental demonstration of nonlinear pulse propagation in a fiber Bragg grating written in a fiber amplifier

We study experimentally nonlinear propagation of sub-nanosecond optical pulses in a fiber Bragg grating written in a Ytterbium-doped fiber amplifier (YD-FBG). The magnitude and the sign of group velocity dispersion (GVD) in YD-FBG can be controlled by adjusting the fiber tension. In the case of anomalous GVD, pulse breakup was observed due to modulation instability. However, for the same input pulse power in the normal GVD regime, the output pulse duration was increased, and pulse breakup was not observed. The deterioration of pulse spectrum due to Raman and four-wave mixing effect was also reduced in the normal GVD regime. Since GVD in YD-FBG is six orders of magnitude higher than in standard fibers, the advantages of normal GVD in fiber amplifiers that were demonstrated in previous works for femtosecond and picosecond pulses can be exploited for amplifying sub-nanosecond pulses. The experimental results are in good agreement with numerical simulations. We have also demonstrated a gain coefficient enhancement by a factor of 1.7 due to slow-light propagation in the YD-FBG.