[1] Aftab Hussain, Chong-xiu Yu, Xiang-jun Xin, Quan-xin Yuan, Bo Liu, Ashiq Hussain, Abdul Latif, Abid Munir, Yousaf Khan and Idress Afridi, Optoelectronics Letters 8, 134 (2012).

[2] Min Feng, Qing-long Luo and Cheng-lin Bai, Optoelectronics Letters 9, 135 (2013).

[3] H. Rohde, S. Smolorz, E. Gottwald and K. Kloppe, Next Generation Optical Access: 1 Gbit/s for Everyone, European Conference on Optical Communications, 10.5.5 (2009).

[4] M. Presi, F. Bottoni, R. Corsini, G. Cossu and E. Ciaramella, IEEE Photonics Technology Letters 26, 107 (2014).

[5] D. Lavery, E. Torrengo and S. J. Savory, Bidirectional 10 Gbit/s Long-reach WDM-PON Using Digital Coherent Receivers, Optical Fiber Communication Conference, OTuB4 (2011).

[6] D. Lavery, R. Mahe, D. S. Millar, B. C. Thomsen, P. Bayvel and S. J. Savory, Journal of Lightwave Technology 31, 609 (2013).

[7] Z. Dong, J. Yu, H. C. Chien, N. Chi, L. Chen and G. K. Chang, Optics Express 19, 11100 (2011).

[8] H. Mu, H. K. Shim, H. G. Choi, U. H. Hong and Y. C. Chung, A Proposal for Cost-Effective 10-Gb/s, 10-GHz Spaced Ultra-Dense WDM PON, Optoelectronics and Communications Conference (OECC), 2013.

[9] M. Fujiwara, J. Kani, H. Suzuki, K. Araya and M. Teshima, Electronics Letters 37, 967 (2001).

[10] K. Y. Cho, Y. Takushima and Y. C. Chung, Electronics Letters 46, 1510 (2010).

[11] S. J. Park, Y. B. Choi, S. P. Jung, K. Y. Cho, Y. Takushima and Y. C. Chung, IEEE Photonics Technology Letters 21, 465 (2009).

[12] K. Y. Cho, K. Tanaka, T. Sano, S. P. Jung, J. H. Chang, Y. Takushima, A. Agata, Y. Horiuchi, M. Suzuki and Y. C. Chung, Journal of Lightwave Technology 29, 456 (2011).