All-polarization-maintaining figure-9 mode-locked fiber laser with tunable wavelengths from 1509 nm to 1612 nm

A widely-tunable mode-locked fiber laser allowing a wavelength tuning range of 103 nm is reported, which is achieved through a reflective grating and cavity loss control. Under the Littrow structure, the grating serves as the feedback arm of the all-polarization-maintaining figure-9 fiber laser, whose angle can be weakly adjusted to achieve continuous tuning from 1509 nm to 1612 nm. The low cavity loss compensates for the low amplification efficiency caused by the off-center gain. This setup facilitates the realization of mode-locking at 1509 nm wavelength, which implies a further extension of the Er-doped laser in the S-band. Our work realizes a mode-locked fiber laser with the widest wavelength tuning range of the 1.5 μm band as far as we know, which is valuable for applications in pulse wavelength extension and specific wavelength acquisition.