1. 1) T. Okoshi and K. Kikuchi: Electron. Lett. 16 (1980) 179.
2. 2) T. Imai, Y. Hayashi, N. Ohkawa, T. Sugie, Y. Ichihashi, and T. Ito: Electron. Lett. 26 (1990) 1407.
3. 3) T. Okoshi and K. Kikuchi: Coherent optical fi ber communications (Kluwer Academic Publishers, 1988).
4. 4) J. G. Proakis: Digital communications (MacGraw Hill, 2000).
5. 5) R. Griffin and A. Carter: Optical Fiber Communication Conf. (OFC 2002), WX6, Anaheim, CA, USA, March 17-22, 2002.