Bragg gratings inscribed in selectively inflated photonic crystal fibers

We report a method for effective fabrication of Bragg gratings in all-silica photonic crystal fibers (PCF). The problem of cladding-hole scattering in PCF grating inscription is avoided by selectively inflating a section of PCF, resulting a locally suspended-core fiber (SCF) region with relatively simple cladding structure. Hence, the inscription laser can laterally access to the core region with little loss. In the SCF regions with core diameter ranging from 2 to 4.5 μm, first-order Bragg gratings are fabricated by use of a phase mask and a focused infrared femtosecond laser with pulse energy as low as ~200 μJ. For the same grating period, samples with different core sizes exhibit different resonant wavelengths and spectral properties, which would enable a range of applications in grating-integrated PCF sensors and devices.