• Chinese Optics Letters
  • Vol. 21, Issue 2, 021404 (2023)
Hongye Li1、2, Xin Tian1、2, Hao Li1、2, Baiyi Wu1、2, Xiaofan Zhao1、3, Meng Wang1、2、3, Chenhui Gao1、3, Binyu Rao1, Xiaoming Xi1, Zilun Chen1, Zefeng Wang1、2、3、*, and Jinbao Chen1
Author Affiliations
  • 1College of Advanced Interdisciplinary Studies, , Changsha 410073, China
  • 2, Changsha 410073, China
  • 3, Changsha 410073, China
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    DOI: 10.3788/COL202321.021404 Cite this Article
    Hongye Li, Xin Tian, Hao Li, Baiyi Wu, Xiaofan Zhao, Meng Wang, Chenhui Gao, Binyu Rao, Xiaoming Xi, Zilun Chen, Zefeng Wang, Jinbao Chen. Fiber oscillator of 5 kW using fiber Bragg gratings inscribed by a visible femtosecond laser[J]. Chinese Optics Letters, 2023, 21(2): 021404 Copy Citation Text show less

    Abstract

    We fabricate a pair of fiber Bragg gratings (FBGs) by a visible femtosecond laser phase mask scanning technique on passive large-mode-area double-cladding fibers for multi-kilowatt fiber oscillators. The bandwidth of high-reflection (HR) and low-reflection (LR) FBG is 1.6 nm and 0.3 nm, respectively. The reflection of the HR-FBG is higher than 99%, and that of the LR-FBG is about 10%. A bidirectional pumped all-fiber oscillator is constructed using this pair of FBGs, a record output power of 5027 W located in the signal core is achieved with a slope efficiency of 82.1%, and the beam quality factor M2 is measured to be 1.6 at the maximum power. The FBGs are simply fixed on a water cooling plate without a special package, and the thermal efficiency of the HR-FBG and the LR-FBG is 2.76°C/kW and 1°C/kW, respectively. Our research provides an effective solution for robust high-power all-fiber laser oscillators.

    1. Introduction

    High-power all-fiber lasers have largely been utilized in industry, scientific research, and defense technology for their high efficiency, good beam quality, and robustness[1,2]. In general, two structures, namely amplifiers and oscillators, are employed to achieve kilowatt (kW)-level fiber lasers. In recent years, benefitting from the large-mode-area (LMA) fiber Bragg gratings (FBGs) fabrication technique, the all-fiber oscillator structure (which is not amplified) has gradually replaced the role of the master oscillator power amplifier (MOPA) structure in many applications[313]. Compared with MOPA, the oscillator has a more compact structure, higher resistance to back-propagating light, and simpler operation. The first, to the best of our knowledge, all-fiber kW-level oscillator was reported by Alfalight company in 2012[4]. After that, the output power of the all-fiber oscillator scaled up step-by-step. The National University of Defense Technology and Fujikura company reported single mode 3 kW all-fiber oscillators in 2017[7,8]. Then, the maximum output power scaled up to the 5 kW level in 2018[9,10]. All-fiber oscillators at the 6 kW level were also realized by suppressing transverse mode instability (TMI) or stimulated Raman scattering (SRS) effects[11,12]. In 2020, Fujikura company realized an 8 kW single mode oscillator using their home-made ytterbium-doped fibers (YDFs) and FBGs[13], which is the maximum output power so far.

    Hongye Li, Xin Tian, Hao Li, Baiyi Wu, Xiaofan Zhao, Meng Wang, Chenhui Gao, Binyu Rao, Xiaoming Xi, Zilun Chen, Zefeng Wang, Jinbao Chen. Fiber oscillator of 5 kW using fiber Bragg gratings inscribed by a visible femtosecond laser[J]. Chinese Optics Letters, 2023, 21(2): 021404
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