[1] [1] J. Canning and M. G. Sceats, Electron. Lett. 30, 1344 (1994).

[2] [2] W. H. Loh and R. I. Laming, Electron. Lett. 31, 1440 (1995).

[3] [3] V. Jayaraman, Z. M. Chuang, and L. A. Coldrem, IEEE J. Quantum Electron. 29, 1824 (1993).

[4] [4] M. Ibsen, M. K. Durkin, M. J. Cole, and R. I. Laming, IEEE Photon. Technol. Lett. 10, 842 (1998).

[5] [5] Y. Z. Yin, Z. Q. Lin, X. F. Chen, L. Xia, X. H. Li, J. Feng, J. Mao, and S. Z. Xie, Acta Opt. Sin. (in Chinese) 22, 1368 (2002).

[6] [6] H. Kogelnik, The Bell System Technical Journal 55, 109 (1976).

[7] [7] D. C. J. Reid, C. M. Ragdale, I. Bennion, D. J. Robbins, J. Buus, and W. J. Stewart, Electron. Lett. 26, 10 (1990).

[8] [8] M. Yamada and K. Sakuda, Appl. Opt. 26, 3474 (1987).