[1] T. Takahashi, T. Imai, and M. Aiki, Electron. Lett. 30, 348 (1994).

[2] F. Heismann, D. A. Fishman, and D. L. Wilson, in Proceedings of ECOC’98 WdC11, 529 (1998).

[3] R. Noe, D. Sandel, M. Yoshida-Dierolf, S. Hinz, V. Mirvoda, A. Schopflin, C. Glingener, E. Gottwald, C. Scheerer, G. Fischer, T. Weyrauch, and W. Haase, J. Lightwave Technol. 17, 1602 (1999).

[4] C. Francia, F. Bruyere, J.-P. Thiery, and D. Penninckx, Electron. Lett. 35, 414 (1999).

[5] N. Kikuchi, J. Lightwave Technol. 19, 480 (2001).

[6] J. C. Rasmussen, A. Isomura, and G. Ishikawa, J. Lightwave Technol. 20, 2101 (2002).

[7] J. C. Rasmussen, in 2003 Digest of the LEOS Summer Topical Meetings 47 (2003).

[8] X. G. Zhang, L. Yu, Y. Zheng, C. Y. Li, G. T. Zhou, Y. Shen, B. J. Yang, H. X Wang, L. Wang, and Y. F. Ji, Acta Photon. Sin. (in Chinese) (to be published).

[9] X. G. Zhang, L. Yu, G. T. Zhou, Y. Shen, Y. Zheng, C. Y. Li, Y. M. Liu, L. Chen, and B. J. Yang, Chin. Opt. Lett. 1, 447 (2003).

[10] H. Kogelnik and R. M. Jopson, in Optical Telecommunications IVB (I. P. Kaminow and T. Li, eds.) (Academic Press, San Diego, 2002) chap. 15.

[11] C. Francia, F. Bruyere, D. Pennickx, and M. Chbat, IEEE Photon. Technol. Lett. 10, 1739 (1998).

[12] H. Sunnerud, C. Xie, M. Karlsson, R. Samuelsson, and P. A. Andrekson, J. Lightwave Technol. 20, 368 (2002).

[13] X. M. Liu, C. Y. Li, R. H. Li, B. J. Yang, and X. G. Zhang, Chin. J. Lasers (in Chinese) 29, 455 (2002).