[1] [1] C. H. Yeh, C. C. Lee, and S. Chi, IEEE Photon. Technol. Lett. 15, 1053 (2003).

[2] [2] C. H. Yeh, C. C. Lee, C. Y. Chen, and S. Chi, IEEE Photon. Technol. Lett. 16, 765 (2004).

[3] [3] J. M. Oh and D. H. Lee, IEEE J. Quantum Electron. 40, 374 (2004).

[4] [4] T. J. Cai, Y. Q. Liu, X. B. Zhang, and T. Y. Wang, Chin. Opt. Lett. 9, 041403 (2011).

[5] [5] H. Wu, N. H. Zhu, J. W. Man, and H. Q. Yuan, IEEE Photon. Technol. Lett. 23, 332 (2011).

[6] [6] M. Zhu, S. L. Xiao, W. Guo, M. H. Bi, Z. Zhou, Y. H. Jin, and W. S. Hu, in Proceedings of Communications and Photonics Conference and Exhibition (ACP) 405 (2010).

[7] [7] C.-H. Yeh, F. Y. Shih, C. H. Wang, C. W. Chow, and S. Chi, Opt. Express 16, 435 (2008).

[8] [8] Y. J. Cao, K. G. Xia, Y. Yao, K.-I. Ueda, and J. L. Li, Chin. Opt. Lett. 9, 041403 (2011).

[9] [9] L. Yi, Z. Li, Y. Dong, S. Xiao, J. Chen, and W. Hu, Opt. Express 20, 10416 (2012).