Fabrication of a bi-directional pump/signal combiner and application in a 4 kW fiber amplifier. (January 2023)

• Record Type: Journal Article
• Authors: Li, Zhixian; Fu, Min; Tian, Xin; Rao, Binyu; Chen, Zilun; Wang, Zefeng; Chen, Jinbao
• Is Part Of: Optics & laser technology. Volume 157(2023)
• Publication Date: 2023-01
• Subjects: Fiber laser -- Fiber combiner; Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2022.108699
• Languages: English
• ISSNs: 0030-3992

Abstract

Highlights: As the key component of the fiber laser system, the bi-directional (6 + 1) × 1 pump/signal combiner has always been a research hotpot. However, it is difficult to maintain the beam quality of signal light in this kind of combiner, which limits its application in high power laser system. In this study, a new method to fabricate a bi-directional (6 + 1) × 1 pump/signal combiner is introduced, which can be applicable to various fiber types. In this method, the non-taper process of signal fiber and in-line alignment splicing ensure the high transmission quality of the signal light. The M 2 value of the signal light degrades for only 2.2 % after passing through the combiner, which is, to the best of our knowledge, the minimum reported value for the same type of the combiner. Besides, the home-made combiner is utilized in a bi-directional pumping fiber amplifier. With 5 kW pump power injecting from the backward, the amplifier output 4 kW power, corresponding to the efficiency of 81.3 %. In addition, the M 2 value of the amplifier remains stable at 1.47 at 4 kW output power with no apparent TMI appears. The maximum temperature point of the home-made combiner lies at the edge of the signal fiber coating with the temperature rise coefficient of 12.1 °C/kW, which demonstrates the outstanding potential of the combiner in high power laser systems. Abstract: We report here a method to fabricate the (6 + 1) × 1 bi-directional pump/signal combiner with high pump coupling efficiency and negligible degradation for the M 2 value of signal light. The pump coupling efficiency for all the six pump fibers is more than 98 %. A CCD camera is firstly used in the alignment fusion process of the fiber bundle and the output fiber, which is precise and convenient. The degradation ratio of the M 2 value of the signal light is 2.2 % after fusion process, which is, to the best of our knowledge, the minimum reported value for the same type of combiner. In addition, the home-made combiner is applied in a counter-directional pumping amplifier, whose maximum output power is 4 kW with the slope efficiency of 81.3 %. The temperature rise coefficient of the home-made combiner is 12.1 °C/kW, indicating the great potential of the combiner in high-power laser applications.