Characterization of femtosecond-inscribed fiber Bragg gratings in the visible spectral region.

The femtosecond-laser pulse inscription and characterization of fiber Bragg gratings for operation at visible wavelengths was performed using several types of optical fibers, including single-mode and graded-index fibers designed for near-infrared wavelengths. The obtained bandwidths are very narrow (∼0.12-0.36  nm) for the used exposure conditions, even in graded-index fibers. Thermal and strain characterization was performed, with results about half of those found for C-band gratings. The wavelength dependence of the sensitivity is compared with a Sellmeier model.