In this paper we report the generation of flat top optical spectrum using an arbitrary waveform generator to increase the SBS threshold in high power optical fiber amplifiers. The optical spectrum consists of a number of discrete spectral lines, ranging from 16 to 380, within the bandwidth of 2GHz, corresponding to line spacing between 133 MHz and 5 MHz. These discrete spectral lines correspond to a PRBS pattern of n = 4 to n = 8. The SBS threshold and coherence properties of the flat top spectrum are measured and compared to that of the filtered PRBS in a kilowatt class fiber amplifier. It is experimentally demonstrated that for large frequency line spacing, the flat top spectrum significantly outperforms the corresponding filtered PRBS, but as the line spacing is decreased to less than the Brillouin bandwidth, the two modulation waveforms have similar enhancement factors in the SBS threshold due to the enhanced crosstalk between neighboring frequency components.
Brian M. Anderson, Rongqing Hui, Angel Flores, and Iyad Dajani, "SBS suppression and coherence properties of a flat top optical spectrum in a high power fiber amplifier," Proc. SPIE 10083, Fiber Lasers XIV: Technology and Systems, 100830V (Presented at SPIE LASE: January 31, 2017; Published: 7 March 2017); https://doi.org/10.1117/12.2252380.
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