Mode instability thresholds for Tm-doped fiber amplifiers pumped at 790 nm

Area of Science:

• Laser physics
• Fiber optics
• Materials science

Background:

• Mode instability (MI) is a critical limitation in high-power fiber amplifiers.
• Thulium (Tm3+)-doped fiber amplifiers offer potential for specific wavelength generation but face challenges.
• Understanding MI thresholds is crucial for optimizing amplifier design and performance.

Purpose of the Study:

• To compute mode instability thresholds in Tm3+-doped fiber amplifiers using a numerical model.
• To compare these thresholds with those in Ytterbium (Yb3+)-doped fiber amplifiers.
• To identify factors contributing to differences in MI thresholds between Tm3+ and Yb3+ systems.

Main Methods:

• Detailed numerical modeling of stimulated thermal Rayleigh scattering.
• Simulation of Tm3+-doped fiber amplifiers operating at 2040 nm signal wavelength with a 790 nm pump.
• Comparison with Yb3+-doped fiber amplifiers (976 nm pump, 1060 nm signal).

Main Results:

• Calculated higher mode instability thresholds for Tm3+-doped fiber amplifiers compared to Yb3+-doped systems.
• Observed high power efficiencies (60%) in Tm3+-doped amplifiers due to strong cross-relaxation.
• Identified longer signal wavelength and stronger gain saturation as key factors for higher Tm3+ MI thresholds.

Conclusions:

• Tm3+-doped fiber amplifiers exhibit enhanced resistance to mode instability.
• Cross-relaxation heating in Tm3+ systems contributes to stronger gain saturation, raising MI thresholds.
• The findings provide insights for designing advanced, high-power fiber amplifiers.