[1] [1] Capmany J, Mora J and Gasulla I, Journal of Lightwave Technology 31, 571 (2013).

[2] [2] Minasian R A, Chan E H W and Yi X, Opt. Express 21, 22918 (2013).

[3] [3] J. Capmany, B. Ortega and D. Pastor, Journal of Lightwave Technology 24, 201 (2006).

[4] [4] J. Yao, Journal of Lightwave Technology 27, 314 (2009).

[5] [5] En-ming Xu, Qi Wang and Fei Wang, Optoelectronics Letters 10, 374 (2014).

[6] [6] Ai-ling Zhang, Cong Huang and Xiao-jun Wu, Optoelectronics Letters 10, 5 (2014).

[7] [7] Xu X, Ou H and Wong K, IEEE Photon. Technol. Lett. 26, 893 (2014).

[8] [8] Feng X, Lu C and Tam H Y, IEEE Photon. Technol. Lett. 19, 1334 (2007).

[9] [9] Xue X, Zheng X and Zhang H, Opt. Express 20, 26929 (2012).

[10] [10] W. Li, N.H. Zhou and L.X. Huang, IEEE Photon. J. 3, 462 (2011).

[11] [11] C. Zhang, L.S. Yan and W. Pan, IEEE Photon. J. 5, 5501606 (2013).

[12] [12] W. Li, L. X. Wang and N. H. Zhu, IEEE Photon. J. 5, 5501411 (2013).

[13] [13] X. S. Yao, IEEE Photon. Technol. Lett. 10, 138 (1998).

[14] [14] W. Zhang and R. A. Minasian, IEEE Photon. Technol. Lett. 23, 1775 (2011).

[15] [15] W. Zhang and R. A. Minasian, IEEE Photon. Technol. Lett. 24, 1182 (2012).

[16] [16] Xiuyou Han and Jianping Yao, Journal of Lightwave Technology 33, 5133 (2015).

[17] [17] E. Xu and J. Yao, IEEE Photon. Technol. Lett. 27, 2063 (2015).

[18] [18] Xia Hao, Zhengrong Tong and Ye Cao, Applied Optics 53, 4519 (2014).

[19] [19] X. Wang, J. Yang and E.H.W. Chan, IEEE Photon. J. 7, 5500411 (2015).