Superluminal optical pulse propagation at 1.5 μm in periodic fiber Bragg gratings

We report on the experimental observation of superluminal tunneling of picosecond optical pulses in a periodic fiber Bragg grating. Optical pulses of 380-ps duration, generated by an externally-modulated single-frequency erbium-ytterbium laser operating near 1.5-μm wavelength, were propagated at a group velocity greater than ~1.97 times the speed of light in vacuum across a 2-cm long fiber grating. Owing to the very large ratio between the thickness of the barrier (2 cm) and the wavelength of probing optical pulses (~1.5 μm), our experiment allows for the observation of superluminal tunneling in the optical region by direct optoelectronic time-domain measurements.