[1] [1] J. Li, J. An, Y. Wu, J. Li, H. Wang, and X. Hu, Chin. Opt. Lett. 8, 588 (2010).

[2] [2] X. Xiao, H. Xu, L. Zhou, Z. Li, Y. Li, Y. Yu, and J. Yu, Chin. Opt. Lett. 8, 757 (2010).

[3] [3] M. Harjanne, M. Kapulainen, T. Aalto, and P. Heimala, IEEE Photon. Technol. Lett. 16, 2039 (2004).

[4] [4] Y. Shoji, K. Kintaka, S. Suda, H. Kawashima, T. Hasama, and H. Ishikawa, Opt. Express 18, 9071 (2010).

[5] [5] Q. Fang, J. F. Sun, T.-Y. Liow, H. Cai, M. B. Yu, G. Q. Lo, and D.-L. Kwong, IEEE Photon. Technol. Lett. 23, 525 (2011).

[6] [6] K. Watanabe, Y. Hashizume, Y. Nasu, M. Kohtoku, M. Itoh, and Y. Inoue, J. Lightware Technol. 26, 2235 (2008).

[7] [7] A. M. Al-hetar, A. B. Mohammad, A. S. M. Supa'at, Z. A. Shamsan, and I. Yulianti, Opt. Commun. 284, 1181 (2011).

[8] [8] N. Xie, T. Hashimoto, and K. Utaka, IEEE Photon. Technol. Lett. 21, 1861 (2009).

[9] [9] L. Gao, J. Sun, X. Sun, C. Kang, Y. Yan, and D. Zhang, Opt. Commun. 282, 4091 (2009).

[10] [10] G. Coppola, L. Sirleto, I. Rendina, and M. Iodice, Opt. Eng. 50, 071112 (2011).