Characterization of the Brillouin-loss spectrum of single-mode fibers by use of very short (< 10-ns) pulses

The characterization of the Brillouin-loss spectrum of single-mode fibers w ith very short (<10-ns) pulses has been studied. It was found that the Bril louin-loss signal intensity is linearly related to the duration of the pump pulse used to obtain the spectrum. In contrast with the uniform trend of t he signal, three distinct behaviors were observed in the spectral linewidth . At long pulse durations the linewidth was constant at approximately 40 MH z. Pulse durations of the order of the phonon lifetime resulted in a broade r spectrum, reaching a maximum width of similar to 100 MHz at 5 ns. Reducin g the pulse duration further resulted in a sudden narrowing of the Brilloui n line. (C) 1999 Optical Society of America.