Coherent beam combining (CBC) is an effective method to improve the output power of fiber lasers while maintaining good beam quality. As interdisciplinary research continues to deepen, the CBC technology of fiber lasers is constantly revitalized, and its application scenarios are becoming increasingly diverse. Reviewing the evolution of fiber laser CBC development and outlining prospective directions for their future development are crucial. This article discusses the development trajectory of the active phase control CBC of fiber lasers, and systematically outlines its development stages from the perspective of literature metrics. The characteristics of each development stage are summarized, and the outlook for future development trends is provided.
Based on an analysis of the literature indexed in the Web of Science Core Collection, the development process for the active phase control CBC of fiber lasers can be divided into four stages: the early stage of academic development, the period of rapid academic development, the stage of stable academic development, and the key stage of technological development.
In the early stage of academic development before 2005, research focused on passive CBC and played an important role in promoting the research on the CBC of fiber lasers. During the period of rapid academic development from 2006 to 2011, researchers proposed various phase-control methods, which solved the basic prerequisite of achieving active phase control. Subsequently, with an increase in the output power, researchers pursued greater combining efficiency and proposed various structures to achieve this goal. At the same time, researchers also explored expanded applications of CBC technology of fiber lasers. During the stage of stable academic development from 2012 to 2016, significant progress was made in the CBC of pulsed fiber lasers. A co-aperture CBC system with higher theoretical efficiency received widespread attention. Researchers proposed many methods to further increase the numbers of combined channels. To improve the combining efficiency, researchers conducted studies on controlling multiple parameters that affect the combining efficiency. In addition, based on the research on the CBC of fiber lasers, researchers gained greater confidence in using CBC technology to obtain ultra-high energy and power, and have proposed various concepts for large scientific installations. In the key stage of technological development after 2017, with the development of CBC technology of fiber lasers, practical breakthroughs have been achieved in various areas such as the numbers of combined channels and combined power. CBC structures with tiled apertures have been widely used in optical-field manipulation. The evolution of nascent disciplines such as artificial intelligence intersects with the development of CBC. The structures and methods continue to improve, and various related products are gradually emerging.
With the development of CBC technology of fiber lasers, the overall trend is characterized by an increasing array scale, improved combined power, improved control parameters, the deepening of interdisciplinary research, and modularization. In terms of the array scale, CBC with thousands or even tens of thousands of beams is a further development trend, driven by various large scientific installations. Regarding combined power, using tiled aperture structures to achieve output power values ranging from hundreds of kilowatts to megawatts has become a practical reality. In terms of controllable parameters, automatic alignment devices with the polarization state adjustment capability and two- or three-dimensional fiber end position adjustment capability are important devices for achieving multidimensional control of fiber laser arrays. In the field of interdisciplinary research, CBC technology has been enriched and developed along with advancements in related technologies. CBC has been shown to be an effective approach to improve laser brightness, which can be utilized in various scenarios. Regarding modularization, modular development can meet different application scenarios and requirements, enabling the rapid construction of fiber laser CBC systems and promoting their application development.
The development process for the active phase control CBC of fiber lasers exhibits significant stage characteristics, with many excellent research achievements emerging at the interval of approximately 5 years. Domestic research institutions have played important roles in promoting its development, such as achieving kilowatt output power and arrays of thousands of beams for the first time. In terms of CBC modules such as single-frequency lasers and narrow linewidth lasers, the highest publicly reported technical indicators have also been achieved. With the continuous maturation of academic development and gradual improvement of technology in the field of the CBC of fiber lasers, unique application value has been demonstrated in areas such as basic scientific research and industrial processing, gradually integrating this technology into social productivity and daily life. Currently, in other countries, scientific devices and products related to the commercial use of CBC are being developed as light sources for basic scientific research and industrial processing. These developments are of great significance in promoting basic scientific research and supporting laser intelligent manufacturing. In the stage where the academic and technological development of the CBC of fiber lasers tends to mature, challenges and opportunities coexist. It is foreseeable that the “CBC+” model, driven by applications and uses in interdisciplinary research, will promote the development of relevant disciplines in the future. This will also lead to a new scientific understanding and technological progress in fiber laser CBC itself.
