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.

Dual-bandgap hollow-core photonic crystal fibers for third harmonic generation.

We present two novel hybrid photonic structures made of silica that possess two well-separated frequency bandgaps. The addition of interstitial air holes in a precise location and size allows these bandgaps to open with a ratio of ∼3 between their central frequencies at the air line ck(z)/w=1, thus fulfilling the basic guidance condition for third harmonic generation in hollow-core fibers. In addition, these designs may serve for high-power laser delivery of two well-separated wavelengths, such as visible and near infrared.