In this study, the loss budget for adopting non-return-to-zero (NRZ) and four-level pulse amplitude modulation (PAM4) in next-generation passive optical networks (NG-PONs) was investigated by simulation and experiment. Through simulation, the signals are distorted by four-wave mixing (FWM) when the zero-dispersion wavelength locates in the middle of the channels. For 25-Gb/s NRZ, a maximal loss budget of approximately 32.5 dB is obtained. For 50-Gb/s PAM4, the bit error rate cannot reach 1 × 10⁻³. While, the impact becomes negligible whens the zero-dispersion wavelength stays away from the middle of the channels, and the loss budget is 36 and 25.7 dB for NRZ and PAM4 systems. Therefore, at least a 32.5-dB loss budget ise obtained in a 4 × 25G NRZ system. While, the loss budget cannot reach the basic requirement of 29 dB in the 4×50G PAM4 system. The experimental resultso verify this conclusion.

通过仿真和实验，研究了下一代无源光网络（NG-PON）中采用不归零（NRZ）和四电平脉冲幅度调制（PAM4）的损耗预算。通过仿真，当零色散波长位于通道中间时，四波混频（FWM）使信号失真。对于25 Gb / s的NRZ，可获得大约32.5 dB的最大损耗预算。对于50 Gb / s PAM4，误码率不能达到1×10 ^-3。同时，当零色散波长远离通道中间时，影响可以忽略不计，对于NRZ和PAM4系统，损耗预算分别为36和25.7 dB。因此，在4×25G NRZ系统中至少可获得32.5 dB的损耗预算。而在4×50G PAM4系统中，损耗预算无法达到29 dB的基本要求。实验结果证实了这一结论。