Jacobsen Gunnar, Xu Tianhua, Popov Sergei, Li Jie, Friberg Ari T, Zhang Yimo
Acreo AB, Electrum 236, SE-16440 Kista, Sweden.
Opt Express. 2012 Apr 9;20(8):8862-70. doi: 10.1364/OE.20.008862.
A radio frequency (RF) carrier can be used to mitigate the phase noise impact in n-level PSK and QAM systems. The systems performance is influenced by the use of an RF pilot carrier to accomplish phase noise compensation through complex multiplication in combination with discrete filters to compensate for the chromatic dispersion (CD). We perform a detailed study comparing two filters for the CD compensation namely the fixed frequency domain equalizer (FDE) filter and the adaptive least-mean-square (LMS) filter. The study provides important novel physical insight into the equalization enhanced phase noise (EEPN) influence on the system bit-error-rate (BER) versus optical signal-to-noise-ratio (OSNR) performance. Important results of the analysis are that the FDE filter position relative to the RF carrier phase noise compensation module provides a possibility for choosing whether the EEPN from the Tx or the LO laser influences the system quality. The LMS filter works very inefficiently when placed prior to the RF phase noise compensation stage of the Rx whereas it works much more efficiently and gives almost the same performance as the FDE filter when placed after the RF phase noise compensation stage.
射频（RF）载波可用于减轻n级相移键控（PSK）和正交幅度调制（QAM）系统中的相位噪声影响。系统性能受射频导频载波的使用影响，通过与离散滤波器结合进行复数乘法来完成相位噪声补偿，以补偿色散（CD）。我们进行了一项详细研究，比较了两种用于CD补偿的滤波器，即固定频域均衡器（FDE）滤波器和自适应最小均方（LMS）滤波器。该研究为均衡增强相位噪声（EEPN）对系统误码率（BER）与光信噪比（OSNR）性能的影响提供了重要的新颖物理见解。分析的重要结果是，FDE滤波器相对于射频载波相位噪声补偿模块的位置为选择来自发射机（Tx）或本地振荡器（LO）激光器的EEPN是否影响系统质量提供了可能性。当LMS滤波器置于接收机（Rx）的射频相位噪声补偿阶段之前时，其工作效率非常低，而当置于射频相位噪声补偿阶段之后时，它工作效率更高，并且性能几乎与FDE滤波器相同。
