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9 November 2016 Experimental investigation of thermally induced core laser leakage in large mode area single trench fiber
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We demonstrated a new phenomenon, namely, thermally induced core laser leakage in single trench fiber (STF), for the first time. The STF provides very high loss and power delocalization of higher order mode (HOM) and maintain the effective single mode operation. However these properties are chartered only under low power situations. In this paper we established a 976nm directly pumped high power co-pumping fiber amplifier based on the STF. The maximum output power was 1022W with a slope efficiency of 76%. Further increase the pump power will leads to the output power decrease. Meanwhile a micro second Level noise like power fluctuation was observed. No resonance frequency was observed in frequency domain indicating the mode instability is not triggered. We believe that it is the thermally induced waveguide index profile change due to the excessively heat load in the front section of STF that leads to the failure of HOM suppression and the power of FM was coupled into the HOM. However the heat load in the rear section of STF was relatively low and the HOM leaked into the cladding due to the bending loss. We provide a mitigating method by pumping with pump light of smaller absorption. A maximum power of 1330W was achieved without power decrease via pumping the STF with 905nm and 976nm pump light (same amplifier). To our best knowledge, this is the first demonstration of thermally induced core laser leakage in STF and the pertinent results can provide significant reference for future optimization.
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Lingchao Kong, Liangjin Huang, Shaoyi Gu, Jinyong Leng, Shaofeng Guo, Pu Zhou, Xiaojun Xu, and Zongfu Jiang "Experimental investigation of thermally induced core laser leakage in large mode area single trench fiber", Proc. SPIE 10016, High-Power Lasers and Applications VIII, 100161M (9 November 2016);

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