Broadband Spectral-Shaping Fiber Laser by Tailoring Cascaded Raman Scattering

Raman fiber lasers harness the spectral agility and transferable gain of stimulated Raman scattering, offering theoretically arbitrary wavelength emission with high spectral customizability. However, their intrinsic spectral degrees of freedom that enable flexible spectral control remain largely unexplored. To unlock this potential, we incorporate a speckle-focusing filter into the laser cavity, leveraging speckle-to-spectrum mapping in multimode fibers to dynamically tailor the cascaded Raman process. Through wavefront-shaping-driven dynamic optimization of the filter response, the laser achieves spectrally defined and reconfigurable emission with fine wavelength selectivity. Our spectral control framework in nonlinear media demonstrates that, without altering the pump wavelength, the spectral profile of individual Stokes orders can be independently shaped. It consequently extends the tuning range of higher-order Stokes while maintaining a favorable spectral purity. Our work reveals a versatile spectral-shaping platform, decoupling Stokes-wavelength tuning from the pump and paving the way for agile sources in spectroscopy, sensing, and nonlinear optics.