Continuous and discrete-point Rayleigh reflectors inscribed by femtosecond pulses in singlemode and multimode fibers

In this paper we present the results on structures inscription to enhance Rayleigh backscattering up to +60 dB in the wide spectral range in singlemode and multimode fibers by tightly focused femtosecond laser radiation. Continuous and discrete-point artificial Rayleigh reflectors were produced and optimized in terms of backscattering enhancement level and insertion losses. The linewidth narrowing of single-frequency DFB Er-doped fiber laser based on the developed 40-cm long artificial Rayleigh reflector in singlemode fiber was demonstrated. Moreover, the various types (1D, 2D, 3D) of localized Rayleigh reflectors were inscribed in the multimode GRIN fiber revealing the strong dependence of backscattering signal on the positions of scattering points in the fiber core cross-section and on the modes composition incident on the reflector. Due to the random distributed feedback based on the developed multimode Rayleigh reflectors, we observed random lasing in 1-km MM GRIN fiber with good (M2 < 3) beam quality at much lower threshold power than that for lasing based on natural Rayleigh backscattering.

Automated summary

In this study, we achieved enhanced Rayleigh backscattering up to +60 dB in a wide spectral range in both singlemode and multimode fibers by using tightly focused femtosecond laser radiation. We produced and optimized artificial Rayleigh reflectors with both continuous and discrete-point structures. In singlemode fiber, we demonstrated linewidth narrowing in a single-frequency DFB Er-doped fiber laser using a 40-cm long artificial Rayleigh reflector. In multimode GRIN fiber, we inscribed various types of localized Rayleigh reflectors and observed the dependence of backscattering signal on the positions of scattering points and the incident modes composition. Random lasing was also achieved in a 1-km MM GRIN fiber with good beam quality, using the developed multimode Rayleigh reflectors.