Peak-power limits on fiber amplifiers imposed by self-focusing

We have numerically investigated the behavior of the fundamental mode of a step-index, multimode (MM) fiber as the optical power approaches the self-focusing limit (P-crit). The analysis includes the effects of gain and bending (applicable to coiled fiber amplifiers). We find power-dependent, stationary solutions that propagate essentially without change at beam powers approaching P-crit in straight and bent fibers. We show that in a MM fiber amplifier seeded with its fundamental eigenmode at powers << P-crit, the transverse spatial profile adiabatically evolves through a continuum of stationary solutions as the beam is amplified toward P-crit. (c) 2006 Optical Society of America.