Abstract:We demonstrate experimentally that it is possible to control optically the group velocity of an optical pulse as it travels along an optical fiber. To achieve this control we use the effect of Stimulated Brillouin Scattering. In our experiments we have achieved changes in the group index of 10 -3 in several kilometer-length fibers, thus leading to pulse delaying and advancement in the range of tens of nanoseconds. We believe that this is the first evidence of such optically-controlled strong delay changes in optical fibers. In this paper we derive the basic theory behind these group-delay changes and we demonstrate the effect in two kinds of fibers which are conventionally used. L. V. Hau, S. E. Harris, Z. Dutton and C. H. Behroozi, "Light speed reduction to 17 metres per second in an ultracold atomic gas," Nature 397, 594-598 (1999). 3.

We report a novel kind of all-optical dynamic grating based on Brillouin scattering in a polarization maintaining fiber (PMF). A moving acoustic grating is generated by stimulated Brillouin scattering between writing beams in one polarization and used to reflect an orthogonally polarized reading beam at different wavelengths. The center wavelength of the grating is controllable by detuning the writing beams, and the 3 dB bandwidth of approximately 80 MHz is observed with the tunable reflectance of up to 4% in a 30 m PMF.

Distributed strain sensing with millimeter-order spatial resolution is demonstrated in optical fibers based on Brillouin optical correlation domain analysis. A novel beat lock-in detection scheme is introduced to suppress background noises coming from the reflection of Brillouin pump waves. The Brillouin frequency shifts of 3 mm fiber sections are successfully measured with a theoretical spatial resolution of 1.6 mm.

Abstract:We demonstrate the generation of slow and fast light based on stimulated Brillouin scattering in As 2 Se 3 chalcogenide fiber with the best efficiency ever reported. The Brillouin gain of 43 dB is achieved with only 60-mW pump power in a 5-m single-mode chalcogenide fiber, which leads to the optical time delay of 37 ns with a 50-ns Gaussian pulse.

Optical fibre sensors based on Brillouin scattering have been vigorously studied in the context of structural health monitoring on account of their capacity for distributed strain and temperature measurements. However, real-time distributed strain measurement has been achieved only for two-end-access systems; such systems reduce the degree of freedom in embedding the sensors into structures, and furthermore render the measurement no longer feasible when extremely high loss or breakage occurs at a point along the sensing fibre. Here, we demonstrate real-time distributed measurement with an intrinsically one-end-access reflectometry configuration by using a correlation-domain technique. In this method, the Brillouin gain spectrum is obtained at high speed using a voltage-controlled oscillator, and the Brillouin frequency shift is converted into a phase delay of a synchronous sinusoidal waveform; the phase delay is subsequently converted into a voltage, which can be directly measured. When a single-point measurement is performed at an arbitrary position, a strain sampling rate of up to 100 kHz is experimentally verified by detecting locally applied dynamic strain at 1 kHz. When distributed measurements are performed at 100 points with 10 times averaging, a repetition rate of 100 Hz is verified by tracking a mechanical wave propagating along the fibre. Some drawbacks of this ultrahigh-speed configuration, including the reduced measurement accuracy, lowered spatial resolution and limited strain dynamic range, are also discussed.

Optically controlled delay lines in optical fibers are demonstrated by use of the group-velocity control of signal pulses based on stimulated Brillouin scattering. We achieve continuous time delay within the range of 150 ns, much larger than the width of the 40 ns signal pulse, using cascaded fiber segments joined by unidirectional optical attenuators. In the meantime, we also observe a large amount of pulse broadening, which agrees well with a theoretical prediction based on linear theory.

Abstract:We report the first experimental demonstration of pulse advancement with gain in optical fibers based on stimulated Brillouin scattering. Two experimental configurations are investigated and compared. One is to make the pulse propagate in a region slightly detuned from a gain peak where the group velocity change is negative and the other is to make use of the large anomalous dispersion appearing between two gain peaks. We experimentally show that the second method produces pulse advancement with lower distortion than the first one.

Broadband slow light is demonstrated by using stimulated Brillouin scattering in optical fibers based on a double Brillouin pump, the peaks of which are spectrally separated by twice the Brillouin frequency. The loss spectrum generated by one of the pump waves is fully compensated by the gain spectrum of the other one, which permits the enlargement of the bandwidth to 25 GHz and a variable time delay of up to 10.9 ps with 37 ps pulses.