Modeling and experiments of actively Q-switched Er3+-Yb3+ codoped clad-pumped fiber lasers

Two models are presented to describe the complex dynamics of Q-switched clad-pumped Er³⁺-Yb³⁺ codoped fiber lasers (EYDFLs): the full model that includes the full wavelength-dependence of parameters in the 1550- and the 1080-nm band due to Er³⁺ and Yb³⁺, respectively, and the simplified model that assumes single wavelengths for both bands. The models are based on detailed rate equations that include energy transfer between Er³⁺ and Yb³⁺ ions, and spontaneous emission due to both Er³⁺ and Yb³⁺. The simplified model is shown to agree with the full model within 10% difference. Experiments are performed using a 4-m-long single-mode clad-pumped EYDFL, and pulse energy of 14.5 μJ is achieved. Excellent agreement is shown between the simplified model and experiments. The model is further used to study the extractable energy of the laser and show limiting factors: amplified spontaneous emission (ASE) and energy storage in Yb³⁺ ions. The model is also used to optimize the pulse energy in terms of fiber length, pump power, and Er³⁺-Yb³⁺ concentrations.