Self-phase modulation in multimode optical fibers produced by moderately high-powered picosecond pulses

Area of Science:

• Nonlinear Optics
• Optical Fiber Communications
• Laser Physics

Background:

• Ultrashort laser pulses undergo spectral changes when propagating through optical fibers.
• Self-phase modulation (SPM) is a key nonlinear effect causing spectral broadening.
• Modal dispersion in multimode fibers can influence pulse propagation dynamics.

Purpose of the Study:

• To investigate and compare the spectral distributions of ultrashort laser pulses in multimode versus single-mode glass fibers.
• To analyze the impact of modal dispersion on spectral broadening caused by SPM.
• To understand the asymmetry in spectral broadening in multimode fibers.

Main Methods:

• Measurement of spectral distributions of 8-picosecond ultrashort laser pulses.
• Propagation experiments in both multimode and single-mode glass fibers.
• Comparison of spectral broadening at comparable laser intensities.

Main Results:

• Spectral broadening from SPM was observed in both fiber types.
• Multimode fibers exhibited asymmetric spectral broadening, predominantly towards the Stokes side.
• Single-mode fibers showed more symmetric spectral broadening under similar conditions.
• Modal dispersion was identified as the cause of the observed asymmetry.

Conclusions:

• Modal dispersion in multimode fibers significantly alters the spectral dynamics of ultrashort laser pulses.
• The asymmetric spectral broadening in multimode fibers is a direct consequence of modal dispersion interacting with SPM.
• Understanding this phenomenon is crucial for applications involving high-intensity ultrashort pulses in optical fibers.