1. See, for example, G. B. Whitham, “Linear and Nonlinear Waves” (John Wiley and Sons, N.Y., 1973) and references therein.
2. S. A. Akhamanov et al, in “Laser Handbook”, F. Arecchi and E. Schulz-Dubois, eds. ( North-Holland, Amsterdam, 1972 ).
3. See, for example, “Fundamentals of Optical Fiber Communications”, M. Barnoski, etc. (Academic, N.Y., 1975 ).
4. A. Yariv, J. Opt. Soc. Am. 66, 301 (1975);
5. A. Gover, C. P. Lee and A. Yariv, J. Opt. Soc. Am. 66, 306 (1975);