Experimental and numerical study of interlock requirements for high-power EYDFAs

Area of Science:

• Optics and Photonics
• Materials Science
• Laser Physics

Background:

• Erbium (Er³⁺) and Ytterbium (Yb³⁺) co-doped fiber amplifiers (EYDFAs) are crucial for high-power laser systems.
• Understanding transient behavior during seed failure is vital for operational safety and system integrity.

Purpose of the Study:

• To investigate the interlock requirements for EYDFAs under seed failure conditions.
• To model the transient gain dynamics and population evolution in EYDFAs post-seed failure.
• To determine critical gain thresholds and their temporal evolution.

Main Methods:

• Utilized a time-dependent Finite Element Method (FEM) tool.
• Incorporated backwards amplified spontaneous emission (ASE) transients from commercial fibers.
• Modeled the Er³⁺:Yb³⁺ system using bi-directional energy transfer and rate equations.
• Computed power evolution and population densities via differential equations.

Main Results:

• Calculated temporal evolution of energy levels and gain after simulated seed failure (tens to hundreds of µs).
• Observed critical total gain of 30 dB within ~80 µs (Yb³⁺ band) and ~300 µs (Er³⁺ band).
• Found that critical gain times decrease with increased pump power and doping concentration.

Conclusions:

• The study quantifies critical gain build-up times in EYDFAs following seed failure.
• Results provide essential data for designing robust interlock systems for high-power EYDFAs.
• Findings are applicable to both core-pumped and cladding-pumped EYDFAs in demanding engineering applications.