Waveguide lasers have the advantages of miniature and compact structure and have broad application prospects in photonic integration and on–chip laboratories. The development of femtosecond laser direct–writing technology makes the processing of transparent materials more flexible and controllable. This paper mainly introduces a waveguide laser based on femtosecond laser direct–writing technology. Firstly, the applications of femtosecond laser direct–writing technology in an optical waveguide are introduced, including the principles of femtosecond laser direct–writing technology, common optical wave scanning methods, and types of optical waveguides. After that, we summarize the development of a waveguide continuous–wave laser, a Q–switched laser and a mode–locked laser from visible to mid–infrared wavebands and analyze some new representative work. Finally, we explain the difficulty of compensating for dispersion in pulse waveguide lasers and summarize some new ideas that have been proposed to solve the problem.

Multimode nonlinear dynamics in spatiotemporal mode-locked (STML) fiber lasers enable exploration of what we believe to be novel solitary waves. However, complex intermodal coupling in multimode fibers prevents precise control over the output parameters of multimode solitons (e.g., mode component and center wavelength), limiting their applications in fiber amplifiers and optical communications. Additionally, vector soliton dynamics have been overlooked due to polarization-dependent saturable absorbers (SAs) in prior STML systems, many unique nonlinear dynamics remain inadequately explained. This work presents a method to customize the output parameters of STML pulses by a spatial alignment structure (SAS). This polarization-independent SAS functions as an SA, spatial filter, and attenuator. Adjusting the SAS enables controllable multimode soliton characteristics and diverse STML dynamics, including soliton rain, tri-color solitons (TCS), and ultra-broad bandwidth spectrum (UBS) pulses (28 nm bandwidth, 94 fs duration) within the same cavity. Experimental results reveal the critical role of vector soliton dynamics in generating parametric sidebands and various STML pulses. This work demonstrates, to our knowledge, the first multimode vector conventional solitons and achieves the broadest bandwidth/shortest pulse duration in 1.5 μm STML lasers. Further research into multifunctional SAS and multimode vector soliton dynamics may uncover what are believed to be new spatiotemporal nonlinear effects, enabling compact, cost-effective STML fiber lasers with on-demand outputs.