Single longitudinal mode lasers by using artificially controlled backscattering erbium doped fibers

In this work, we propose and experimentally demonstrate a new distributed short linear cavity fiber laser. At one of the cavity ends, fabricated by a commercial femtosecond fiber laser chirped pulse amplifier, an artificially controlled backscattering erbium doped fiber section has been connected. This distributed reflector acts also as a saturable absorber, leading to the generation of tunable and switchable single longitudinal-mode laser emissions. The distributed reflector consists of 9 micro-drilled sections of about 1cm each one and randomly spread throughout 2 meters of highly doped erbium fiber. The total length of the fiber laser is 9.5 m and the laser shows a single mode behavior at all the emitted wavelengths. Using this new kind of reflecting saturable absorber, single and multiple single-mode emissions can be obtained. The achieved laser presents a pump threshold as low as 45 mW and shows up to 8 different single-mode emission lines with an optical signal to noise ratio of 45dB.This work was supported in part by the MINECO/AEI (Ministerio de Economía y Competitividad/Agencia Estatal de Investigación), Spain, under Grant TEC2016-76021-C2-1-R, Grant TEC2016-76021-C2-2-R, and Grant PID2019-107270RB; in part by the Ministerio de Educación, Cultura y Deporte of Spain under Grant FPU2018/02797, and in part by the Projects for Young Researches UPNA 2019 (Universidad Publica de Navarra) and FEDER Funds (European Regional Development Fund)