Mode-locked, dual-wavelength fiber laser with a dual-repetition rate of 1.3/1.4 um in a space-division multiplexing cavity.

Dual-color mode-locked fiber lasers are widely applied in various domains, including difference-frequency generation, Raman scattering spectroscopy, and microscopy. A dual-color mode-locked laser can be obtained through a shared main path along with dedicated subpaths, which pumps either a single or multiple gain media, offering a more flexible design and a simpler structural configuration. In this Letter, we demonstrated a dual-repetition rate of a 1.3/1.4 µm mode-locked fiber laser based on a nonlinear polarization rotation (NPR) technology in a bismuth (Bi)-doped fiber by a space-multiplexed cavity. By utilizing the extensive luminescent properties of Bi-doped fibers, the laser can deliver mode-locked pulses with repetition rates of 3.18 and 2.62 MHz and central wavelengths of 1314.60 and 1410.76 nm, respectively. Besides, by fine-tuning polarization controllers (PCs) and pump power, we can also achieve Q-switched pulses with a distinct repetition rate for the 1.3/1.4 µm bands. This compact and cost-effective all-fiber laser system may have significant potential for practical applications in the fields of optical communication, difference-frequency generation, microscopy, etc.