Research progress of mode-locked pulsed fiber lasers with high damage threshold saturable absorber

Abstract

As the basic hardware to promote the development of various fields, fiber laser has great development potential in rail transit, optical communication, new material manufacturing, power battery processing, military defense, medical treatment, and other fields. As the core device of passively mode-locked fiber laser, a high damage threshold saturable absorber plays a decisive role in achieving high power, ultrashort pulse duration, and high energy laser output for a fiber laser. For saturable absorbers of traditional materials and structures, the spot size of light acting on the material is almost the same as the exit diameter of the optical fiber, which is easy to exceed the damage threshold of the saturable absorber and lead to damage. To improve the damage threshold of saturable absorbers, the structure of saturable absorbers based on both real materials and traditional saturable absorbers can be optimized. On the one hand, the preparation technology of the saturable absorber is adjusted, such as using the sol-gel method, which has a good effect on improving the damage threshold of the saturable absorber. Moreover, different materials are selected and used as substrates, such as the use of inorganic materials as material substrates and the selection of a variety of insertion cavity structures, such as “sandwich” transmission structures, tapered fibers, and photonic crystal fibers. These methods are of great significance in improving the damage threshold of the real material saturable absorber and realizing pulsed laser with excellent performance and high stability. On the other hand, the equivalent saturable absorber structure is used to improve the damage threshold and optimize the laser performance, such as hybrid mode-locked structure and nonlinear multimode interference. The continuous optimization of the fiber laser damage threshold will further expand its application range. Therefore, it is important to adjust the preparation process and insert the cavity structure of saturable absorbers for improving the damage threshold of the saturable absorber and achieving high performance and stability of the pulsed laser. This paper reviews the research status of high damage threshold saturable absorbers at home and abroad, summarizes the latest methods to improve material damage threshold and the latest research progress of equivalent saturable absorbers, and also points out the future development direction of high damage threshold saturable absorbers.