Inoue Takashi, Namiki Shu
Opt Express. 2014 Jun 30;22(13):15376-87. doi: 10.1364/OE.22.015376.
A novel carrier recovery scheme for demodulating optical M-ary quadrature amplitude modulation (M-QAM) signals is proposed and demonstrated. The proposed scheme treats a certain number of consecutive symbols as a processing block for which linear evolution of the carrier phases in time is assumed. The Kalman filter algorithm is employed to simultaneously estimate the carrier-frequency offset and carrier phases of the symbols in each block from the observation result. Consequently, an optimal carrier recovery operation with minimum mean squared error can be obtained, and large phase errors due to optical noise and large carrier-frequency offsets can be tolerated. We experimentally demonstrate the proposed scheme in demodulating optical 16- and 64-QAM signals, confirming its stable operation for carrier-frequency offsets even larger than 10% of the symbol rate of the signal. We also demonstrate 160-km transmission of a single-channel, single-polarization 64-QAM signal by using the proposed scheme in the demodulation process.
提出并演示了一种用于解调光M进制正交幅度调制（M-QAM）信号的新型载波恢复方案。该方案将一定数量的连续符号视为一个处理块，并假设载波相位在时间上呈线性演变。采用卡尔曼滤波算法根据观测结果同时估计每个块中符号的载波频率偏移和载波相位。因此，可以获得具有最小均方误差的最优载波恢复操作，并且可以容忍由于光噪声和大载波频率偏移引起的大相位误差。我们通过实验演示了该方案在解调光16-QAM和64-QAM信号中的应用，证实了其对于甚至大于信号符号率10%的载波频率偏移也能稳定运行。我们还通过在解调过程中使用该方案演示了单通道、单偏振64-QAM信号的160公里传输。
