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

Area of Science:

• Nonlinear optics
• Optical fiber physics
• Computational electromagnetics

Background:

• Understanding high-power optical beam propagation in multimode (MM) fibers is crucial for applications like fiber amplifiers.
• The self-focusing limit (P(crit)) represents a critical threshold where nonlinear effects significantly alter beam behavior.
• Gain and fiber bending introduce additional complexities to beam propagation dynamics.

Purpose of the Study:

• To numerically investigate the behavior of the fundamental mode in a step-index MM fiber as optical power approaches the self-focusing limit (P(crit)).
• To analyze the influence of optical gain and fiber bending on the fundamental mode's propagation.
• To identify and characterize stationary solutions that emerge at high power levels.

Main Methods:

• Numerical simulations of the fundamental mode in a step-index MM fiber.
• Analysis of beam propagation under conditions of optical gain and fiber bending.
• Investigation of power-dependent, stationary solutions near P(crit).

Main Results:

• Power-dependent, stationary solutions were identified that propagate stably as power approaches P(crit) in both straight and bent fibers.
• For MM fiber amplifiers seeded with the fundamental eigenmode at low powers, the transverse spatial profile evolves adiabatically.
• This adiabatic evolution leads to a continuum of stationary solutions as the amplified beam approaches P(crit).

Conclusions:

• Stationary, power-dependent solutions exist for the fundamental mode in MM fibers near the self-focusing limit, even with gain and bending.
• The transverse spatial profile of the fundamental mode in a MM fiber amplifier adiabatically evolves towards these stationary states as power increases.
• These findings are significant for understanding and designing high-power fiber amplifiers and managing nonlinear effects.