[1] D. Pureur, M. Douay, P. Bernage, P. Niay, and J. F. Bayon, J. Lightwave Technol. 13, 350 (1995).

[2] T. Ning, L. Pei, X. Hu, Y. Ruan, C. Qi, S. Feng, O. Xu, and S. Lu, Chinese J. Lasers (in Chinese) 35, 1868 (2008).

[3] S Yamashita and G. J. Cowle, J. Lightwave Technol. 17, 509 (1999).

[4] D. Y. Stepanov, J. Canning, and L. Poladian, Opt. Fiber Technol. 5, 209 (1999).

[5] H. Story, B. Sahlgren, and R. Stubbe, Electron. Lett. 33, 56 (1997).

[6] A.Wang, H. Ming, F. Li, L. Xu, L. L¨u, H. Gui, J. Huang, and J. Xie, Chin. Opt. Lett. 2, 223 (2004).

[7] J. K. Sahu, C. C. Renaud, J. Nilsson, W. A. Clarkson, S. A. Alam, and A. B. Grudinin, in Conference on Lasers and Electro-Optics 2001, 322 (2001).

[8] Y. O. Barmenkov, A. V. Kir’yanov, J. Mora, J. L. Cruz, and M. V. Andr′es, IEEE Photon. Technol. Lett. 17, 28 (2005).

[9] P. Ou, Y. Jia, B. Cao, C. Zhang, S. Hu, and D. Feng, Chin. Opt. Lett. 6, 845 (2008).

[10] X. Mao, F. Yan, L. Wang, S. Feng, J. Peng, and S. Jian, Opt. Commun. 282, 93 (2009).

[11] S. Feng, O. Xu, S. Lu, X. Mao, T. Ning, and S. Jian, Opt. Express 16, 11830 (2008).

[12] S. Feng, O. Xu, S. Lu, X. Mao, T. Ning, and S. Jian, Opt. Laser Technol. 41, 264 (2009).

[13] L. Sun, X. Feng, W. Zhang, L. Xiong, Y. Liu, G. Kai, S. Yuan, and X. Dong, IEEE Photon. Technol. Lett. 16, 1453 (2004).