Ultrafast Laser-Fabricated Three-Dimensional Photonic Chips Empowering Diverse Applications

Three-dimensional (3D) photonic integration is becoming a key enabler for future optical technologies, driven by the need for greater functionality, higher compactness, and superior interconnect density. In response to these demands, ultrafast laser processing has emerged as a powerful technique for realizing 3D photonic chips with enhanced design and fabrication flexibility—while avoiding the complexity of mask-based or cleanroom-dependent fabrication. This review begins by outlining the fundamental mechanisms of femtosecond laser–matter interactions, which enable precise energy deposition and spatially confined material modification. It then delineates three primary processing routes—direct modification, additive processing, and subtractive processing—alongside essential beam-shaping strategies. The compatibility of various material systems and structural platforms, including glasses, polymers, crystals, bulk substrates, thin-film layers, and optical fibers, is further discussed. Subsequently, the review details how these 3D laser-fabricated photonic structures underpin a wide range of applications, such as optical field manipulation, optical communications, optical interconnects, optical computing and processing, optical data storage, quantum information, nonlinear optics, optical trapping, and imaging. Finally, it concludes with a perspective on the prevailing challenges and future trends toward scalable, multifunctional, and hybrid-integrated photonic systems enabled by ultrafast laser microfabrication.