Impact of the Overall Electrical Filter Shaping in Next-Generation 25 and 50 Gb/s PONs

Next-generation high-speed passive optical networks (HS-PONs) supporting 25, 50, and 100 Gb∕s are in the early stages of their standardization process. One key aspect under discussion is the choice of the best modulation format for the transceivers. Performance comparisons among several modulation formats against different physical constraints have been presented in literature and are still being examined. In our present contribution, we performed an exhaustive analysis on the impact of the electrical frequency response of transceivers on the performance of two-level pulse amplitude modulation (PAM-2), 4-level PAM (PAM-4), electrical duobinary, and optical duobinary modulation formats with adaptive equalizers on the receiver side. We show, by means of numerical simulations, that the specification of the typically used −3 dB bandwidth is insufficient, since out-of-band electrical frequency response specifications (such as the −20 dB bandwidth) have a huge impact on the performance of the analyzed modulation formats. We believe that the normalized performance graphs given at the end of the paper in terms of −3 dB and −20 dB bandwidths can thus be useful for the design of next-generation HS-PON transceivers.