Dense multiwavelength bismuth-doped phosphosilicate fiber laser near 1360 nm using a femtosecond-laser-inscribed...

We report the experimental demonstration of a stable, dense multiwavelength bismuth-doped phosphosilicate fiber laser operating near 1360 nm. The system utilizes a short-grating Fabry-Pérot interferometer (FBG-FPI) as an intra-cavity comb filter, fabricated via a femtosecond-laser point-by-point direct writing method. To overcome the bandwidth limitations imposed by conventional long-grating filters, the FBG-FPI features a highly compact structure comprising two 0.15 mm grating reflectors separated by a 4.0 mm cavity, inscribed directly through the fiber coating. The laser generates 10 distinct lasing lines from 1360.03-1361.40 nm with a 0.152 nm channel spacing, aligning exceptionally well with the 25 GHz ITU-T DWDM grid. All channels exhibit OSNR above 42 dB, negligible wavelength drift, and peak-power fluctuation below 1.95 dB over 60 min, providing a practical route to stable dense multiwavelength sources.