Inscribing an output coupler grating directly through the fiber coating with a 266  nm femtosecond laser

We inscribe with 266 nm femtosecond pulses a ∼0.75% output coupler for a 1550 nm fiber laser directly through the coating of an SMF-28. The output coupler was inscribed with the phase-mask technique without H₂ loading. This output coupler was spliced to an active Er/Yb fiber, and a fiber laser with an output power of ∼6.4  W and a slope efficiency of ∼30% was obtained. To the best of our knowledge, this is the first reported attempt to inscribe a fiber Bragg grating through the polymer jacket of an optical fiber with a UV femtosecond laser.