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Wavelength-switchable erbium-doped fiber laser based on femtosecond FBG inscribed on fiber core and cladding through the coating

Wavelength-switchable and multiple-wavelength outputs from fiber laser systems have many potential applications but, at present, methods for their generation are quite complex. Here we propose a simple approach, demonstrating a dual-wavelength switchable erbium-doped fiber laser that incorporates a single fiber Bragg grating (FBG), fabricated by a femtosecond laser in a plane-by-plane inscription method through a fiber coating, for a switchable 1564.66 and 1562.87 nm dual-wavelength laser operation. An 800 nm femtosecond pulsed laser acts as the inscription laser, focused by a 63×  oil lens, fabricating a first-order FBG with an interval of 541 nm directly, on both the fiber core and cladding, through the polyimide coating. A 4 m-long erbium-doped fiber was selected as the gain medium. A lasing threshold of 66 mW was used in the experiment, and a switchable laser with stable single- and dual-wavelength outputs was achieved by adjusting a polarization controller. We were able to generate two different single-wavelength lasers with power fluctuations lower than 0.09 dB when measured over 40 min. In addition, dual-wavelength laser output could be obtained with power shifts of less than 0.9 dB at 26 °C.