A numerical study of laser cooling in a large mode area Single Mode Photonic Crystal Yb3+:ZBLAN glass fiber is presented. In a recent analyses on conventional single mode fibers (SMFs), strategies to maximize the cooling efficiency were highlighted and it was shown that the cooling scales quadratically with the core and inversely with the cladding radius. For conventional SMFs, heat source density can hardly be increased due to limitations in the total Yb doping concentration and the fact that the system easily operates in the pump saturation regime due to very low saturation intensities in small core single mode fibers. Therefore, it is essential to use the largest possible core radius and smallest cladding radius to obtain detectable cooling. A trivial design approach to obtain large mode areas is to decrease the numerical aperture (NA). However, there are several difficulties in applying this concept to rare-earth-doped fibers. Here, we propose large mode area single mode Yb3+:ZBLAN photonic crystal fibers as a robust alternative design. The radial distribution of the pump and laser mode intensities are numerically calculated using Finite Element Method and the heat source density is directly calculated using the pump and laser intensity distributions. The heat source density is fed back to the heat transfer module of COMSOL and radial temperature distribution across the large core of the fiber and its surrounding photonic crystal structure is calculated. Our results show that a much higher laser cooling efficiency is achievable in large mode area single mode photonic crystal fibers.
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