Abstract

Optical modulational instability (MI),¹ the spontaneous generation of intensity modulation on a continuous wave, has received much attention recently as a novel nonlinear optical process and as a source of high repetition rate subpicosecond pulses. In a detailed analysis² it was pointed out that MI would only be seen for anomalous group velocity dispersion (GVD). This effect was first observed in the nonlinear propagation of infrared light in optical fibers.³ The situation of two waves nonlinearly coupled via cross-phase modulation in a birefringent fiber was treated⁴ for anomalous GVD. A straightforward extension of this analysis shows that MI occurs even for normal dispersion. In the spectral domain, the slow wave develops a single sideband frequency down-shifted, whereas for the fast wave it is up-shifted. This behavior is in contrast to previously observed optical MI³ where the pump develops dual sidebands, and thus the present system represents a new class of MI.

© 1990 Optical Society of America