Characterization and optimization of Yb-doped photonic-crystal fiber rod amplifiers using spatially resolved spectral interferometry

摘要

Spatially resolved spectral interferometry is used to measure the mode content of a Yb-doped photonic-crystal fiber rod amplifier with a 2300 (mu)m~(2) mode area. The technique, known as S~(2) imaging, was adapted for the short fiber amplifier at full power and revealed a small amount of a copolarized LP_(11) mode. Simulations illustrate the potential for weak mode suppression in this fiber and agree qualitatively with the measurements of S~(2) and M~(2). Higher-order-mode content depends on the alignment of the input signal at injection and ranged from -18 dB for optimized alignment to -13 dB when the injection alignment was offset along the LP_(11) axis by 30percent of the 55 (mu)m mode-field diameter.