1.3/1.4 μm bismuth-doped mode-locked fiber laser with a tunable-wavelength range exceeding 100 nm

The tunable-wavelength mode-locked laser source in the 1.3/1.4 μm spectral region is highly sought after for its critical applications in optical communications, biophotonics, and spectroscopy. A novel, to the best of our knowledge, bismuth(Bi)-doped phosphorus-silicate fiber offers a broadband emission spectrum covering 1280-1460 nm, which is an ideal gain medium for a light source in this band. Here, we demonstrate a 1.3/1.4 μm all-fiber tunable-wavelength Bi-doped mode-locked fiber laser with a tuning range exceeding 100 nm, achieved using a Lyot filter. The laser can be tuned over two separate wavelength bands (1321.32-1369.05 nm and 1419.45-1471.98 nm). Moreover, the pulse dynamics and evolution processes are directly visualized in real-time using the Time-Stretch Dispersive Fourier Transform (TS-DFT) technique, revealing distinct pulse formation times across the tuning range. This work significantly advances Bi-doped fiber laser technology by combining ultra-broad tunability, all-fiber integration, and real-time pulse evolution insight, thereby offering a promising light source platform for future wavelength-division multiplexed (WDM) optical networks and multispectral biomedical imaging systems.