Study of Grating Based Side-coupling Technology for High Power Laser Diode Array
Date Issued
2015
Date
2015
Author(s)
Yang, Song-Pu
Abstract
In recent years, diode-pumped fiber lasers have become main-stream in the high-power laser field, owing to their superior beam quality, narrow linewidth, and high electrical-optical conversion efficiency. Besides, laser diode array (LDA) is a reliable high-power pump source, and it has been widely used in many applications. In 2011, we have demonstrated a side-coupling scheme, a 50% coupling efficiency was achieved by using 680-nm period gold-embedded grating to couple 21-W, 976-nm LDA pump source into a 400-μm double-clad passive fiber. But in such a system, there was coupling loss caused by the secondary diffraction. The issue made it harder to couple pump source into a small cladding fiber. In this work, we achieve 67.63% coupling efficiency into a 400-μm fiber by using a 675-nm grating. In addition, even using the fiber with the cladding diameter to 250 μm, the coupling efficiency is as good as the above mentioned case. In this result, the brightness has been enhanced by a factor of 2.36. Secondly, we introduce a genetic algorithm to optimize the grating coupling efficiency by eliminating the secondary diffraction and index-matching-gel coupling loss. We design an asymmetrical ±1st-order-diffraction-efficiency grating to increase +1st order diffraction efficiency, and reduce the coupling loss caused by the use of index-matching gel. Finally, we discuss the correlation between coupling loss issues and system structure parameters to achieve a high brightness, high power fiber laser output with a compact side coupling system.
Subjects
high-power fiber laser
laser diode array
grating
grating coupler
diffraction
Type
thesis
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