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Femtosecond (fs) laser inscription technology allows for the production of in-fiber disordered structures with an enhanced level of Rayleigh backscattering with relatively few induced losses. These properties enable the application of these structures as reflectors in fiber lasers. In this study, a narrow-linewidth erbium fiber laser with random distributed feedback provided by a fs-induced random structure in a ring cavity configuration was developed. A single-frequency regime was observed over the entire lasing power range. At a maximum output power of 7.8 mW, the linewidth did not exceed 0.75 kHz.

A distributed Bragg reflector (DBR) laser with a specially designed, heavily Er3+-doped composite fiber of a length as short as 1.8 cm is demonstrated. The DBR laser, pumped by a 980 nm laser diode with power of up to 370 mW, generates single-frequency radiation at a wavelength of 1535 nm with a narrow instantaneous linewidth of 3+-doped fiber laser parameters pave the way toward a broad range of practical applications from telecommunications and sensing to scientific research.

We present our theoretical model and experimental results on the extreme linewidth narrowing of an erbium-doped fiber distributed feedback (DFB) laser due to an additional random DFB via Rayleigh backscattering in a long single-mode fiber connected to the laser. The relative narrowing of instantaneous (–3 Hz in the hybrid configuration, with the lower limit defined by the background electrical noise. Significant narrowing was also observed for the long-term ≥10 μs) linewidth directly measured by the self-delay heterodyne technique: the values for the DFB laser and hybrid configuration amount to 6 kHz and 160 Hz, respectively.