Spectrally programmable Raman fiber laser with adaptive wavefront shaping

Raman fiber lasers(RFLs)have broadband tunability due to cascaded stimulated Raman scattering,providing extensive degrees of freedom for spectral manipulation.However,the spectral diversity of RFLs depends mainly on the wavelength flexibility of the pump,which limits the application of RFLs.Here,a spectrally programmable RFL is developed based on two-dimensional spatial-to-spectral mapping of light in multimode fibers(MMFs).Using an intracavity wavefront shaping method combined with genetic algorithm optimization,we launch light with a selected wavelength(s)at MMF output into the active part of the laser for amplification.In contrast,the light of undesired wavelengths is blocked.We demonstrate spectral shaping of the high-order RFL,including a continuously tunable single wavelength and multiple wavelengths with a designed spectral shape.Due to the simultaneous control of different wavelength regions,each order of Raman Stokes light allows flexible and independent spectral manipulation.Our research exploits light manipulation in a fiber platform with multieigenmodes and nonlinear gain,mapping spatial control to the spectral domain and extending linear light control in MMFs to active light emission,which is of great significance for applications of RFLs in optical imaging,sensing,and spectroscopy.