This study successfully prepared high-purity Nb 4 C 3 Tx saturable absorber (SA) using an acid-etching method. The modulation depth is 13.07 %, with a saturation intensity of 1.62 MW/cm 2 , demonstrating significant nonlinear saturable absorption characteristics. The SA device was integrated into an erbium-doped fiber laser, where we successfully captured stable traditional soliton mode-locking and 59th–63rd order continuous harmonic modelocking (HML) operations. At a pump power of 203 mW, the traditional soliton has a central wavelength of 1563.89 nm and a repetition frequency of 6.70 MHz. At a pump power of 500 mW, the highest repetition frequency of the HML is 421.4 MHz. In addition, the data comparison reveals that the introduction of specific functional groups has a significant impact on the mode-locking performance. Experimental results indicate that Nb 4 C 3 Tx-SA exhibits excellent saturable absorption properties, providing a new modulation material for the development of high repetition frequency ultrafast fiber lasers.
Wei et al. (2026) studied this question.