Photosensitive highly Er/Yb co-doped phosphosilicate optical fibers for continuous-wave single-frequency fiber laser applications

Highly Er/Yb co-doped phosphosilicate fibers with low optical losses were fabricated by the MCVD method, utilizing an all-gas-phase deposition technique developed "in house." Important characteristics such as photodarkening and photosensitivity of these fibers were thoroughly investigated. An almost negligible impact of photodarkening-induced losses (no more than 1 dB/m) was discovered in the near-infrared spectral region. The photosensitivity of hydrogen-loaded fiber samples was studied using excimer laser irradiation at a wavelength of 193 nm. A photoinduced refractive index value of 1 x 10(-3) at the total UV irradiation exposure dose of 550 J/cm(2) was achieved. A single-frequency laser with a Fabry-Perot short cavity was designed by inscribing highly reflective (R > 99.9%) and partially reflective (R = 94.3%) fiber Bragg gratings directly in the Er/Yb co-doped phosphosilicate fiber core. The laser showed stable CW output emitting with a narrow peak centered at 1551.5 nm in the absence of any signs of Yb3+ parasite lasing in awavelength range from 1000 to 1100 nm. (C) 2020 Optical Society of America