Opt Lett. 2019 Jan 15;44(2):307-310. doi: 10.1364/OL.44.000307.
We present a laser phase noise (PN) induced effect of a phase-modulation-to-intensity-modulation conversion noise and noise pedestals underneath each of the orthogonal frequency division multiplexing (OFDM) subcarriers in a self-coherent optical OFDM transmission using a self-homodyne technique. We provide a statistical analysis on the received symbols using a histogram to demonstrate the effect of a phase rotation term and inter-subcarrier interference individually and collectively. The PN is then compensated using a simple time delay to realign the phase walk-off of the subcarriers relative to the carrier. Significant quadrature improvements of 6.82 dB using 5 MHz laser linewidth over a 720 km transmission length and 5.38 dB using 20 MHz over 240 km have been obtained with 16 quadrature amplitude modulation (QAM) over 15 GHz OFDM signal bandwidth. The technique also significantly reduced an optical-signal-to-noise ratio requirement at the bit error rate of 1×10 by 16.15 dB for 64-QAM over 160 km. With the delay, the system can tolerate three times the chromatic dispersion-length product.
我们提出了一种激光相位噪声（PN）引起的相位调制到强度调制转换噪声和正交频分复用（OFDM）子载波下的噪声基底的影响，这些噪声基底存在于自相干光 OFDM 传输中使用自外差技术。我们使用直方图对接收符号进行了统计分析，以分别和集体演示相位旋转项和子载波间干扰的影响。然后，通过简单的时延来补偿 PN，以使子载波的相位游走相对于载波对齐。在 720 km 的传输长度上，使用 5 MHz 激光线宽获得了 6.82 dB 的显著正交改进，在 240 km 上使用 20 MHz 获得了 5.38 dB 的改进，在 15 GHz OFDM 信号带宽上使用 16 正交幅度调制（QAM）。该技术还显著降低了误码率为 1×10 的光信噪比要求，对于 160 km 上的 64-QAM ，降低了 16.15 dB。通过时延，系统可以容忍三倍的色度色散长度乘积。
