All-optically reconfigurable Er³⁺-doped single-frequency fiber laser with 100-nm tuning via self-adaptive dynamic gratings

Single-frequency fiber lasers (SFFLs) are vital for precision metrology, optical clocks, and ultra-dense wavelength division multiplexing (UD-WDM) due to their ultra-narrow linewidth and high coherence. However, traditional SFFLs based on static filters suffer from a fundamental trade-off between wavelength tunability and spectral purity, limiting their practical tuning ranges to below 40 nm, despite much broader gain bandwidths in rare-earth-doped fibers. Here, we report an all-optically reconfigurable Er³⁺-doped SFFL that achieves an unprecedented tuning range of 100.12 nm (1512.84-1612.96 nm), enabled by self-adaptive dynamic gratings (SADGs) formed through nonlinear intermodal coupling and spatial hole burning in unpumped fiber. Theoretical modeling and experiments reveal that SADGs provide automatic, mode-selective feedback that maintains continuous single-longitudinal-mode (SLM) without mechanical tuning. The laser features a 3 kHz linewidth, 16 pm tuning precision, 30 nm/s tuning speed, and <0.5% power fluctuation, demonstrating stable, narrow-linewidth emission across the S + C + L bands. This work substantially mitigates the long-standing tunability-coherence trade-off and establishes a generalizable framework for all-optically controlled high-coherence laser systems, paving the way for next-generation photonics in UD-WDM, quantum metrology, and reconfigurable optical networks.