Gbps/\(\lambda\) PON Downstream C-Band Direct-Detection Links with \(\geq\)29 dB Power Budget  
[PERSON]  
1 Department of Electronics and Telecommunications, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (P.T.-F.); [EMAIL_ADDRESS] (V.F. ); [EMAIL_ADDRESS] (R.G.) [PERSON]  
1 Department of Electronics and Telecommunications, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy; [EMAIL_ADDRESS] (H.W. ); [EMAIL_ADDRESS] (P.T.-F.); [EMAIL_ADDRESS] (V.F. ); [EMAIL_ADDRESS] (R.G.) [PERSON]  
1 LINKS Foundation, [PERSON] 61, 10138 Torino, Italy12 University of Illinois, Chicago, Illinois 106067, USA12 University of Illinois, Chicago, Illinois 106067, USA12 University of Illinois, Chicago, Illinois 106067, USA12 University of Illinois, Chicago, Illinois 1060  
compensation of CD, power-fading effect and other impairments through digital signal processing, thus enabling C-band operation. In [18; 19; 20], the possibility of using coherent detection has been studied. However, due to the high cost and complexity, the use of coherent detection in the cost-effective PON environment is still under discussion [9; 18]. In a recent work [15], we proposed chromatic dispersion digital pre-compensation (CD-DPC) for 100 Gbps links using a dual-arm in-phase and quadrature Mach-Zehnder modulator (IQ-MZM) at the transmitter (TX) side while keeping DD at the receiver (RX). This approach only increases complexity at the optical line termination (OLT) side, which in the PON downstream scenario is shared among the end users. Increasing the target data rate requires pushing the system into nonlinear operation [16; 17; 21] to be able to increase the transmitter launch power and the optical modulation index to achieve the demanding power-budget requirements. In [16], we analyzed simple nonlinear compensation techniques, i.e., square-rootlike (SQRT) and polynomial (POLY) techniques. We simulatively and experimentally confirmed about 2 dB gain in terms of maximum optical distribution network (ODN) loss for a 100 Gbps downstream transmission, thanks to SQRT and POLY. Next generation PONs must be backward compatible with legacy PONs, and the ODN must remain the same. Typically, at least a 29 dB link power budget (budget class N1) and a 0 to (at least) 20 km fiber reach must be guaranteed [1; 22; 3; 4]. Regarding the trend of ITU-T PON standardization evolution, at least a 4-fold increment in DS capacity can be observed between 2 consecutive PON system generations [2; 4]. For example, there is a 4-fold increment in DS capacity from a GPON (with DS 2.5 Gbps per \(\lambda\)) to XG(S)-PON (with DS 10 Gbps per \(\lambda\)), and a 5-fold increment from a XG(S)-PON to a higher speed PON (with DS 50 Gbps per \(\lambda\)). Therefore, it is expected that the next generation beyond 50G-PON will target (at least) 200 Gbps per \(\lambda\) in DS. To meet the 29 dB ODN loss and 20 km fiber reach at 100 Gbps is very challenging, as we showed in previous works [14; 15; 16; 17]. For a 200 Gbps per \(\lambda\) transmission, the situation becomes extremely critical. In this paper, we focus on 200 Gbps per \(\lambda\) transmission in a C-band to guarantee 29 dB ODN loss over a 20 km fiber link, by combining the CD-DPC algorithm with two nonlinear distortion compensation techniques: the SQRT [16] and the Volterra nonlinear equalizer (VNLE) [17]. In [17], for 100 Gbps per \(\lambda\) transmission in a C-band, we experimentally showed a 1-2 dB gain in term of ODN loss by using VNLE when compared to the SQRT. Until now, non-return-to-zero on-off-keying (NRZ-OOK) modulation format has been defined for all standardized PONs. It is expected that 50G class optoelectronics (O/E) will be commercially available by the time 200 Gbps products are developed. However, devices to support OOK and 4-level pulse amplitude modulation (PAM-4) operations at 100 Gbaud or beyond seems difficult to achieve in the midterm [3; 23].