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Development of an All‐Fiber Coherent Beam Combining System toward High Energy Pulse Fiber Lasers
Author(s) -
KAMBAYASHI YUTA,
YOSHIDA MINORU,
INOUE TATSUKI
Publication year - 2017
Publication title -
electronics and communications in japan
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.131
H-Index - 13
eISSN - 1942-9541
pISSN - 1942-9533
DOI - 10.1002/ecj.11930
Subject(s) - optics , laser beam quality , fiber laser , laser , optical fiber , materials science , polarization maintaining optical fiber , optical path , m squared , femtosecond , physics , fiber optic sensor , laser beams
SUMMARY Our present work develops an all‐fiber coherent beam combining (CBC) system to achieve a high energy pulse fiber laser beyond pulse energy limits due to nonlinear effects in rare‐earth‐doped fibers. Coherent beam combining is a power addition technology that obtains high energy density and high beam quality because it integrates multiple laser beams in a monolight wave. However, the CBC using optical fibers is technically difficult because the optical phases and polarization in optical fibers fluctuate due to disturbances. Therefore, we developed a novel all‐fiber CBC system that can precisely control optical path lengths and automatically compensate polarization changes. When the system combined four laser pulses, it achieved a beam‐combining efficiency of 96.6% that was about four times as high as a pulse energy before combining. In addition, the system obtained 97.1% beam‐combining efficiency of CBC using femtosecond pulses that have very low coherences by minimizing the optical path‐length differences between combined two pulses. Moreover, the system successfully regulated the beam‐combining‐efficiency changes to less than 2.0 percentage points in full width by suppressing optical path‐length fluctuations and tracking‐control of the optical phases.