A wavelength-tunable 1-μm ultrashort-pulse fiber laser can be used not only in laser spectroscopy, optical measurements, biomedicine, and other fields, but also as a seed source in the field of ultrashort-pulse solid-state lasers to accurately match the emission peaks of different gain media. Currently, ultrashort-pulse fiber lasers mainly rely on mode-locking techniques such as nonlinear polarization evolution (NPE), nonlinear amplifying loop mirrors (NALMs), and semiconductor saturable absorption mirrors (SESAMs). Wavelength-tunable 1-μm ultrashort-pulse lasers can be constructed by adding corresponding wavelength-tunable items such as interference items, gratings, and bandpass tunable filters. However, these add complexity and cost to the system. This study utilizes the characteristics of gain saturation amplification related to chirp pulses to realize a wavelength-tunable 1-μm polarization-maintaining (PM) ultrashort-pulse fiber laser based on a pump beam splitting structure. The wavelength-tunable 1-μm ultrashort-pulse fiber laser is relatively simple in structure and has the ability to adjust the central wavelength continuously and accurately, which can match the emission peaks of gain crystals such as Yb∶YAG, Yb∶CaF₂, and Yb∶Lu₂O₃. The proposed laser is expected to provide a more compact, portable, and stable seed light source for ultrashort-pulse solid-state lasers.

Based on the pump beam splitting structure, an innovative wavelength-tunable ultrashort-pulse fiber laser is realized using the gain saturation amplification effect of chirp pulses. The laser consists of an ultrashort-pulse fiber oscillator, energy controller, and ultrashort-pulse fiber amplifier, which is driven by a semiconductor laser based on a beam-splitting structure. Controlling the chirp pulse energy injected into the amplifier enables the amplifier to operate in a gain-saturation or non-saturation state, and the central wavelength of the laser can be accurately adjusted.

When the laser diode (LD) power is increased to 364.5 mW, which corresponds to pump power of 72.6 mW and 291.9 mW for the oscillator and amplifier, respectively, stable ultrashort pulses are obtained at a repetition rate of 36.23 MHz for the ultrashort-pulse fiber laser. When the energy controller is adjusted, the center wavelength of the ultrashort-pulse laser can tune from 1030.0 nm to 1034.5 nm with a spectral width of >13.1 nm. The corresponding output power changes from 50 mW to 156 mW, and the Fourier transform limited (FTL) pulse widths over the entire wavelength tuning range are approximately 100 fs (Fig. 3). When the output power is 50 mW, the central wavelength of the output spectrum is exactly 1030 nm, which accurately matches the emission peaks of Yb∶YAG and Yb∶CaF₂. When the output power is 100 mW, the central wavelength is exactly 1032 nm, which is consistent with the emission peak of Yb∶Lu₂O₃. Notably, the signal-to-noise ratio (SNR) of the ultrashort pulses at each wavelength is greater than 55 dB, indicating that the ultrashort-pulse fiber laser has very high stability. In addition, when the output power is 50, 100, and 156 mW, the corresponding pulse width is 7.1, 7.2, and 7.5 ps, respectively (Fig. 4). Because of the stable passive mode-locking and PM fiber structure, the obtained 1-μm ultrashort-pulse laser exhibits good power stability. When the output power is 156 mW, the relative jitter is as low as 0.1% within 5 h (Fig. 5).

This study utilizes the characteristics of gain saturation amplification related to chirp pulses to report a wavelength-tunable 1-μm PM ultrashort-pulse fiber laser based on a pump beam splitting structure. Adjustments to the chirp pulse energy injected into the amplifier enable the amplifier to operate in a gain-saturated or non-saturated state, whereby the laser produces wavelength-tunable pulses from 1030.0 nm to 1034.5 nm at a spectral bandwidth of >13.1 nm. Over the entire tuning range, the SNR of the amplified pulses exceeds 55 dB and the pulse width changes from 7.1 ps to 7.5 ps. In addition, because of the PM architecture, the 1-μm ultrashort-pulse laser source exhibits good long-term power stability of as low as 0.1%. The output wavelength of the laser can accurately match the emission peaks of gain crystals such as Yb∶YAG, Yb∶CaF₂, and Yb∶Lu₂O₃. This laser system can serve as a more compact, portable, and stable seed source for ultrashort-pulse solid-state lasers based on various gain crystals such as Yb∶YAG, Yb∶CaF₂, and Yb∶Lu₂O₃.