[1] Ε Ρ Ippen et al., Appl. Phys. Lett.; 21, 348(1972)

[2] R L, Pork el al., Appl. Phys. Lett.. 33, 671(1981)

[3] Ching-yun Wang et al., Opt. Commun. to bepublished

[4] Ching-yun Wang et al.. Opt. Commun.. to bepublished

[5] W Dietel et al., Opt. Commun., 50, 179(1984)

[7] R L Pork et al., Opt. Lett., 9, 150(1984)