We report the first observation of modulational instability of lightwave propagation in single-mode fibers. Modulational instability In fiber, predicted by Hasegawa and Brinkman,1 results from the interplay of the Kerr nonlinearity and anomalous (or negative) group-velocity dispersion. The theory predicts that a cw (or long-pulse) lightwave becomes unstable with respect to a small modulation in the anomalous dispersion region. (For a standard fiber this corresponds to the wavelength of minimum loss.) In the experiment, we used the light from a mode-locked Nd:YAG laser operated at 1.319 μm, which outputs 100-ps pulses at 100 MHz. These pulses provide a quasi-cw condition, since the pulse duration is much longer than the expected modulation period (~2 ps). We took the approach of introducing no initial modulation and simply monitoring the growth of the instability from spontaneous emission.
© 1986 Optical Society of AmericaPDF Article