A theoretical model to describe in-band pumped holmium doped silica fiber lasers is presented. The model is established based upon theory and parameters obtained from published research works. Both core-pumped system and cladding-pumped system are simulated with the model. The simulation results agree well with most experimental results, and for the cases in which the simulation results show discrepancy with the experimental results the disagreement can be reasonably explained. Through numerical analysis it is found that besides common negative factors such as non-radiative decay, fiber loss, and non-optimized resonator configuration, energy transfer upconversion plays a deleterious role in the performance of in-band pumped holmium doped silica fiber lasers. In particular, inhomogeneous upconversion associated with ion clustering is found to cause significant degradation of slope efficiencies of lasers, a fact that is useful to understand the unsolved problem regarding the lower-than-expected slope efficiencies observed in previous studies of in-band pumped holmium doped fiber lasers.
Manuscript received July 11, 2018; accepted October 16, 2018. Date of publication October 24, 2018; date of current version November 28, 2018. This work was supported by the R&D Program funded by the Korea Institute of Science and Technology (2E28070). (Corresponding author: Kwanil Lee.) J. Wang is with the Department of Physics, Ajou University, Suwon 16499, South Korea, and also with the Nanophotonics Research Center, Korea Institute of Science and Technology, Seoul 02792, South Korea (e-mail:,alphafirefox@ gmail.com).
