Fast and slow light in optical fibers through tilted fiber Bragg gratings

In this paper, slow and fast light in optical fiber through tilted fiber Bragg grating (TFBG) are reported. The experimental results show the capability of TFBGs to enable group velocity control of an optical pulse in optical fiber, due to the anomalous dispersion features induced by the coupling between the propagating core mode and each counter-propagating coupling cladding mode. In particular, superluminal propagation of a pulse train has been observed at optical communication wavelengths with time advancements in the picoseconds time scale in 1cm long TFBG and group velocity as large as about two times the speed of light in optical fiber (approximately 1.3 x c0). Very good agreement has been obtained comparing the measured group delay of the TFBG with the one retrieved from the amplitude response through Hilbert transform. Finally, tunable slow and fast light has also been reported, demonstrating the possibility to control the group velocity at single wavelength through both fluidic and thermal actuation.