With the development of the new generation of mobile communication technology, there is an increased demand for bandwidth, speed, and latency in passive optical networks (PONs). Wavelength-division multiplexing PON (WDM-PON) which utilizes frequency resources for bandwidth allocation can assign different channels to different optical network units (ONUs) simultaneously. This eliminates time slot competition among ONUs, reduces system latency, and holds promise for addressing high-latency issues. An embedded communication channel called the auxiliary management and control channel (AMCC) has been proposed and successfully implemented in WDM-PON to enable the transmission of management and control information at a lower cost without altering the frame structure. In recent years, there has been increasing attention to frequency-division multiplexing coherent PON (FDM-CPON), which also supports bandwidth allocation in the frequency domain. To complete AMCC transmission in FDM-CPON, we put forward two simple and cost-effective transmission mechanisms of transmission management and control signal for FDM-CPON, including the addition and multiplication of AMCC and data channel at the digital end. Meanwhile, we conduct a comparative analysis on the performance of these two transmission mechanisms in a 200 Gbit/s FDM-CPON system based on 16QAM transmission over 20-km fiber. The research results provide references for AMCC transmission and system design of high-speed FDM-CPON in the future.

To implement the two transmission mechanisms and conduct a comparative analysis on their performance in a 200 Gbit/s FDM-CPON system based on 16QAM transmission over a 20-km fiber, we generate 16QAM and on-off keying (OOK) signals for the transmission of data channel and AMCC at the digital end respectively. After mapping the low level in OOK to 1 and the high level to a real number greater than 1, the OOK signal can be up-sampled to the same length as the data channel signal. By multiplying bitwise, the combination of multiplication-based AMCC and the data channel can be achieved. For addition-based AMCC, the low level in OOK should be mapped to 0, while the high level is mapped to a complex number with both real and imaginary parts greater than 0. This mapped signal is then added bitwise to the data channel signal. After the combination of AMCC and the data channel, the signal is received by an integrated coherent receiver (ICR) over a 20-km fiber. At the receiver, the amplitude of the received signal is extracted, and the amplitude variations of the signal are obtained by smoothing filtering. After energy detection and inverse mapping, the decoding of the OOK signal is completed. Simultaneously, the received signal undergoes the classical coherent digital signal processing (DSP) for decoding. Additionally, we modify the modulation index (MI) and bandwidth of AMCC at the transmitter, studying the performance of the two transmission mechanisms in different conditions.

We test the sensitivity curves of data channel signals overlaid with both multiplication-based AMCC and addition-based AMCC under different MIs, as well as the Q curves of OOK signals transmitted by AMCC. Under the same receiver optical power (ROP) and MI, the influence of multiplication-based AMCC on the sensitivity of the data channel signal is smaller. Simultaneously, the Q value of OOK transmitted by multiplication-based AMCC is greater than that of addition-based AMCC. We also experimentally verify the effect of the MI and bandwidth of AMCC on the sensitivity of the data channel signal and the Q value of AMCC. Under the same MI and bandwidth, the data channel signal combined with multiplication-based AMCC exhibits higher sensitivity and power budget than the data-channel signal combined with addition-based AMCC. Meanwhile, the larger MI and bandwidth lead to a greater influence of AMCC on the performance of the data-channel signal. When the MI of AMCC is set at 26.1% with a corresponding bandwidth of 24.4 MHz, the effect of multiplication-based AMCC on signal sensitivity is 3 dB lower than that of addition-based AMCC.

We verify and compare the effects of multiplication-based AMCC and addition-based AMCC on the performance of the data channel signal and the OOK signal transmitted by AMCC in a high-speed FDM-CPON. Experimental results from a 200 Gbit/s FDM-CPON system based on 16QAM transmission over 20-km fiber indicate that multiplication-based AMCC has a smaller influence on the sensitivity and power budget of the data-channel signal, with higher Q value of the AMCC-transmitted signal. When the MI of AMCC is set at 26.1% with a corresponding bandwidth of 24.4 MHz, the effect of multiplication-based AMCC on signal sensitivity is 3 dB lower than that of addition-based AMCC. Additionally, experiments are conducted to assess the effect of different MIs and bandwidths of AMCC on the sensitivity of the data-channel signal, with results consistent with the conclusions drawn from theoretical analysis. The results provide significant references for AMCC transmission and system design of high-speed FDM-CPON in the future.