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  • Received: Jun. 24, 2020

    Accepted: Aug. 6, 2020

    Posted: Aug. 10, 2020

    Published Online: Sep. 23, 2020

    The Author Email: Seongwoo Yoo (seon.yoo@ntu.edu.sg), Song-Liang Chua (csonglia@dso.org.sg)

    DOI: 10.1364/PRJ.400755

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    Kang-Jie Lim, Samuel Kai-Wen Seah, Joash Yong’En Ye, Wendy Weiying Lim, Chu-Perng Seah, Yunn-Boon Tan, Suting Tan, Huiting Lim, Raghuraman Sidharthan, Arumugam Rajendra Prasadh, Chen-Jian Chang, Seongwoo Yoo, Song-Liang Chua. High absorption large-mode area step-index fiber for tandem-pumped high-brightness high-power lasers[J]. Photonics Research, 2020, 8(10): 10001599

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Photonics Research, Vol. 8, Issue 10, 10001599 (2020)

High absorption large-mode area step-index fiber for tandem-pumped high-brightness high-power lasers

Kang-Jie Lim1,†, Samuel Kai-Wen Seah1,†, Joash Yong’En Ye1, Wendy Weiying Lim1, Chu-Perng Seah1, Yunn-Boon Tan1, Suting Tan1, Huiting Lim1, Raghuraman Sidharthan2, Arumugam Rajendra Prasadh1, Chen-Jian Chang2, Seongwoo Yoo2,3,*, and Song-Liang Chua1,4,*

Author Affiliations

  • 1DSO National Laboratories, 118225 Singapore, Singapore
  • 2School of Electrical and Electronic Engineering, Nanyang Technological University, 639798 Singapore, Singapore
  • 3e-mail: seon.yoo@ntu.edu.sg
  • 4e-mail: csonglia@dso.org.sg

Abstract

A short absorption length ytterbium (Yb)-doped large-mode area (LMA) fiber is presented as a step forward to mitigate the stern problem of nonlinear scatterings in a tandem pumping scheme adopted for high-power fiber laser. The short absorption length was realized by incorporating high Yb concentration in the fiber core. Furthermore, by replacing the inherent silica cladding with a Ge-doped cladding, we were able to obtain low core numerical aperture (NA) and negate the detrimental effect of index-raising by high Yb concentrations. This overcomes the long-standing limitation in step-index Yb-doped fibers (YDFs) where high cladding absorption inevitably results in high NA, thus hampering single-mode operation. We report an LMA (575 μm2) YDF with NA of 0.04 and absorption of 27 dB/m at 976 nm—both traits promote power scaling of single-mode tandem pumped fiber lasers. To our knowledge, this is the highest cladding absorption attained in a low-NA step-index fiber to date. An all-fiber tandem-pumped amplifier was built using only 14 m of the YDF. The amplifier delivered a near-Gaussian beam (M21.27) at 836 W output power (pump power limited) with a high slope efficiency of 83%. Thanks to the short length and the tandem pumping, no indication of limiting factors such as stimulated Raman scattering, photodarkening, and transverse mode instability was observed.

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