[1] Sotiropoulos N. Koonen A M J, de Waardt H. Next-generation TDM-PON based on multilevel differential modulation[J]. IEEE Photonics Technology Letters, 25, 418-421(2013).

[2] Cvijetic N. OFDM for next-generation optical access networks[J]. Journal of Lightwave Technology, 30, 384-398(2012).

[3] Xiao Y Q, Wang Z Y, Cao J et al. Time-frequency domain encryption with SLM scheme for physical-layer security in an OFDM-PON system[J]. Journal of Optical Communications and Networking, 10, 46-51(2018).

[4] Han M X, Wu Y T, Zhang Q W et al. Secure algorithm for suppressing peak-to-average power ratio in OFDM-PON systems[J]. Acta Optica Sinica, 39, 0506004(2019).

[5] Zhang L J, Xin X J, Liu B et al. Secure OFDM-PON based on chaos scrambling[J]. IEEE Photonics Technology Letters, 23, 998-1000(2011).

[6] Zhang J Q, Marshall A, Woods R et al. Design of an OFDM physical layer encryption scheme[J]. IEEE Transactions on Vehicular Technology, 66, 2114-2127(2017).

[7] Etemad S, Agarwal A, Banwell T et al. An overlay photonic layer security approach scalable to 100 Gb/s[J]. IEEE Communications Magazine, 46, 32-39(2008).

[8] Cheng M F, Deng L, Gao X J et al. Security-enhanced OFDM-PON using hybrid chaotic system[J]. IEEE Photonics Technology Letters, 27, 326-329(2015).

[9] Liu B, Zhang L J, Xin X J et al. Piecewise chaotic permutation method for physical layer security in OFDM-PON[J]. IEEE Photonics Technology Letters, 28, 2359-2362(2016).

[10] Cheng M, Deng L, Wang X et al. Enhanced secure strategy for OFDM-PON system by using hyperchaotic system and fractional Fourier transformation[J]. IEEE Photonics Journal, 6, 1-9(2014).

[11] Zhang W, Zhang C F, Chen C et al. Experimental demonstration of security-enhanced OFDMA-PON using chaotic constellation transformation and pilot-aided secure key agreement[J]. Journal of Lightwave Technology, 35, 1524-1530(2017).

[12] Zhang L J, Xin X J, Liu B et al. Physical secure enhancement in optical OFDMA-PON based on two-dimensional scrambling[J]. Optics Express, 20, B32-B37(2012).

[13] Deng L, Cheng M F, Wang X L et al. Secure OFDM-PON system based on chaos and fractional Fourier transform techniques[J]. Journal of Lightwave Technology, 32, 2629-2635(2014).

[14] Sultan A, Yang X L. Hajomer A A E, et al. Dynamic QAM mapping for physical-layer security using digital chaos[J]. IEEE Access, 6, 47199-47205(2018).

[15] Zhang C F, Zhang W, Chen C et al. Physical-enhanced secure strategy for OFDMA-PON using chaos and deoxyribonucleic acid encoding[J]. Journal of Lightwave Technology, 36, 1706-1712(2018).

[16] Chen Q H, Bi M H, Fu X S et al. Security scheme in IMDD-OFDM-PON system with the chaotic pilot interval and scrambling[J]. Optics Communications, 407, 285-289(2018).

[17] Hu Z Y, Chan C K. A 7-D hyperchaotic system-based encryption scheme for secure fast-OFDM-PON[J]. Journal of Lightwave Technology, 36, 3373-3381(2018).

[18] Cao P, Hu X F, Wu J Y et al. Physical layer encryption in OFDM-PON employing time-variable keys from ONUs[J]. IEEE Photonics Journal, 6, 1-6(2014).

[19] Bi M H, Fu X S, Zhou X F et al. A key space enhanced chaotic encryption scheme for physical layer security in OFDM-PON[J]. IEEE Photonics Journal, 9, 1-10(2017).