Ultrafast Polarization‐Maintaining Fiber Lasers: Design, Fabrication, Performance, and Applications

Abstract Ultrafast polarization‐maintaining fiber lasers (UPMFLs), with superior optical performance and high immunity to environmental disturbances, are highly preferable in a variety of industrial and scientific applications such as high‐precision micromachining and biomedical imaging. Especially, the utilization of PM fibers endows the laser intrinsic stability, thereby enabling the construction of robust and low‐noise optical frequency comb systems. To meet more demanding application challenges, continuous efforts have been invested in the design and fabrication of UPMFLs, aiming to reach unprecedented levels of various pulse parameters, that is, to achieve shorter pulse duration, higher or lower repetition rate, and higher pulse energy. This review presents a detailed overview of different passive mode‐locking techniques for pulsed operation and the most significant achievements in UPMFLs. Representative advances at 1.0, 1.55, and 2.0 µm spectral regions are presented and summarized. The state‐of‐the‐art lasing performance is application‐oriented, and conversely, optical improvements in all‐PM pulsed lasers promote emerging applications, which are also discussed and analyzed. How to overcome the bottlenecks of UPMFLs in terms of pulse duration, repetition rate, emission wavelength, and pulse energy to make them powerful tools for physical, medical, and biological applications remains challenging in the future.