Transverse mode instability considering bend loss and heat load.

Area of Science:

• Optics and Photonics
• Fiber Laser Technology
• High-Power Laser Systems

Background:

• Transverse mode instability (TMI) limits output power in fiber amplifiers.
• Previous models did not account for bend loss, especially significant in narrow-core fibers.
• Local heat load influences bend loss and TMI thresholds.

Purpose of the Study:

• To develop a TMI model that includes bend loss effects.
• To investigate the impact of local heat load on bend loss and TMI.
• To provide new insights into TMI thresholds in advanced fiber amplifiers.

Main Methods:

• Integration of a finite element method (FEM) mode solver for bend loss calculation.
• Incorporation of stimulated thermal Rayleigh scattering and quasi-3D fiber amplifier models.
• Analysis of 3D gain saturation effects and heat-load-induced bend loss reduction.

Main Results:

• Bend loss is highly sensitive to fiber core diameter and local heat load.
• The developed model accurately predicts TMI thresholds considering bend loss.
• New insights into the interplay between heat load, bend loss, and TMI were obtained.

Conclusions:

• Bend loss is a critical factor in TMI for small-core fibers.
• Accurate modeling of TMI requires considering heat-load-induced bend loss.
• The enhanced model provides a more comprehensive understanding of high-power fiber amplifier limitations.