Significance High-power fiber lasers offer many advantages: high-power output, excellent beam quality, high optical efficiency, high degree of integration, high reliability, and spatial compactness. Fiber lasers have therefore been widely adopted for both scientific and commercial applications including material processing, free space communication, and military defense. Among the different kinds of fiber laser, the GTWave is especially popular for its significant power scalability and flexible structure design. This paper reviews the results of high-power GTWave fiber lasers across the world; their characteristics and merits are analyzed through comparison with conventional double cladding fiber lasers. Future directions of research on GTWave fiber lasers are additionally discussed.
Progress The construction of GTWave fiber is detailed in
The concept of using optical fibers to evanescently couple pump energy from laser diodes to a solid-state laser rod was proposed by U.S. Naval Research Laboratory in 1991, but the University of Southampton made the first GTWave fiber, and Southampton Photonics Inc. manufactured many high-power fiber lasers that demonstrated the high injected pump power and high-power scalability of GTWave fiber lasers. Southampton Photonics Inc. manufactured a 2 kW GTWave fiber oscillator in 2016; its stimulated Raman scattering (SRS) level was low, and the transverse mode instability (TMI) had been mitigated. The IPG Photonics Corporation also developed GTWave fiber very early, and manufactured a 2 kW fiber laser in 2006, which showed the flexible structure design of GTWave fiber and displayed massive injected pump power. They created the first 10 kW high-power GTWave fiber laser in 2009, which was much more powerful than other fiber lasers. The Chinese National University of Defense Technology developed a homemade 1 kW GTWave fiber laser in 2014, and obtained a 4 kW GTWave fiber oscillator and main oscillator power amplifier (MOPA) by multi-stage bidirectional pumping in 2018. Although the China Academy of Engineering Physics’ research on GTWave fiber started relatively late, they adopted multi-pump fiber schemes to develop GTWave fiber and developed a (2+1) GTWave fiber 2 kW MOPA laser in 2016. They obtained a 10.45 kW (8+1) GTWave fiber MOPA laser in 2018.
Many other organizations have paid much attention to GTWave fiber lasers; however, the technology requires much investment and technology, and as a result most can do only theoretical research. The Russian Academy of Sciences developed a 100 W GTWave fiber laser in 2005, and made many low-power fiber components in early years, but no results have been reported of late.
Conclusion and Prospect The above research shows that the development of GTWave fiber lasers is very fast, and that their power scalability is so strong that their output power is much higher than that of other fiber lasers. The output power of GTWave fiber has grown to 10 kW within 10 years. We analyze the characteristics and merits of GTWave fiber lasers through comparison with conventional double cladding fiber lasers. Although the conventional double cladding fiber laser has exceeded 5 kW for the reverse combiners commercialized in recent years, GTWave fiber lasers are still more suitable for bidirectional pumping and multi-injected ports by means of multi-stage cascaded amplifiers or multi-pump fiber schemes. As the pump light is coupled gradually to the active GTWave fiber, the heat is well-distributed along the fiber, which is more suitable for a high-power fiber laser.
The development process of GTWave fiber is very complicated, and the price is very high at present. This limits the research of GTWave fiber lasers to only a few organizations. With the development of high-power fiber lasers, people have paid more attention to GTWave fiber both theoretically and experimentally. We believe that the commercialization of GTWave fiber will come in the near future, as more and more people conduct research on GTWave fiber lasers.
