Ming Jun, Xiao Jiangnan, Wu Dongyan, Wang Leilei, Zhou Ye, Zhao Li
Opt Express. 2022 Oct 24;30(22):39663-39678. doi: 10.1364/OE.473283.
An independent sideband (ISB) is a promising scheme for short-reach and metro applications because of its high spectral efficiency, low complexity, and tolerance to chromatic dispersion. Here, we develop a signal synthesis scheme to further reduce the complexity of ISB direct-detection (DD) systems. Two lower-order quadrature amplitude modulation (QAM) sideband signals are generated digitally, then the left sideband (LSB) and right sideband (RSB) are modulated with regular quadrature phase shift keying (QPSK) and geometrically shaped shifted QPSK (GS-S-QPSK), respectively. Then, the two independent sideband signals are received in a single photodiode to synthesize a GS-16QAM signal. The LSB and RSB signals can be separated and demodulated by a digital signal process (DSP) instead of using two optical bandpass filters. The proposed scheme significantly reduces the complexity of the ISB-DD receiver, thus saving system cost. Three different GS-S-QPSK signals are evaluated, with the square GS-S-QPSK achieving the best bit error rate (BER) with its optimal shaping factor. Considering signal-signal beating interference, a sub-blind K-means clustering algorithm is used to improve the BER performance, and the results indicate that it can achieve a large received optical power (ROP) gain at a threshold of 3.8 × 10.
独立边带（ISB）由于其高频谱效率、低复杂度以及对色散的耐受性，是一种适用于短距离和城域应用的很有前景的方案。在此，我们开发了一种信号合成方案，以进一步降低ISB直接检测（DD）系统的复杂度。通过数字方式生成两个低阶正交幅度调制（QAM）边带信号，然后分别用常规正交相移键控（QPSK）和几何形状移位QPSK（GS-S-QPSK）对左边带（LSB）和右边带（RSB）进行调制。接着，在单个光电二极管中接收这两个独立边带信号，以合成一个GS-16QAM信号。LSB和RSB信号可通过数字信号处理（DSP）分离和解调，而无需使用两个光学带通滤波器。所提出的方案显著降低了ISB-DD接收机的复杂度，从而节省了系统成本。对三种不同的GS-S-QPSK信号进行了评估，方形GS-S-QPSK凭借其最佳整形因子实现了最佳误码率（BER）。考虑到信号间拍频干扰，使用了一种次盲K均值聚类算法来提高BER性能，结果表明在3.8×10的阈值下它可以实现较大的接收光功率（ROP）增益。
