Very high speed PON is the PON generation in the ITU-T that is coming after 50G-PON. It is currently in the exploratory study phase in ITU, with network operators sharing their views on potential requirements and the Q2/SG15 group proposing and evaluating technology candidates to meet these requirements. This paper reviews the progress so far in identifying the key requirements, technical candidates, physical layer transmission performance, and the related technology maturity. The paper discusses the technology candidate evaluation process underway as part of this pre-standardization, research phase of very high speed PON among the relevant standards experts within FSAN and ITU-T SG15/Q2.

This paper systematically reviews the evolution, standard development, application scenario expansion, and system capability improvement of GPON, 10G-PON, and 50G-PON from the perspective of carriers, and looks forward to the future development trend.

This paper provides an update on the progress of Very High Speed PON (VHSP) in the ITU-T. Emerging requirements coming from network operators and the various technology candidates to meet them are reviewed.

We present an initial evaluation of the two main technologies for $200 G$ optical access networks: IMDD and coherent. We consider the emerging requirements from operators and review how both options meet them.

We report the first large-scale network field trial demonstrating the evolution of 10G EPON to 50G PON using a newly two-generation multi-PON module, which validates the sustainable evolution for mass 10G EPON networks.

In a first system configuration, a dedicated 50G-PON module was incorporated into the OLT, seamlessly coexisting with commercial G-PON and XGS-PON. The coexistence of the three generations of PONs is done here without adding any loss (filter) in existing ODNs, the 50G-PON being inserted on a 2:2 splitter at the CO. Furthermore, the possibility to extend the reach and place the 50G-PON OLT in a remote CO is evaluated. The second system uses a MPM at the OLT that includes the three PON generations. To our knowledge, this is the first full G-PON, XG(S)-PON, 50G-PON system prototype that provides an optical budget of 29 dB, and we demonstrate the possibility of extending the budget to 35 dB using SOAs.

We evaluate TDEC and Rx sensitivity in a negative dispersion regime with 25G-class DML and EML modulated at 50 Gb/s. Results show that TDEC can effectively predict the performance of both transmitters for 50G-PON upstream.

We analyze the metrology of transmitter and dispersion eye closure (TDEC) as defined in a 50G passive optical network (50G-PON) for assessing transmitter quality. First, we present a theoretical evaluation for adapting TDEC to 50G-PON, where equalized bandwidth limited avalanche-photodiode-based receivers are expected. We optimize the parameters for a proper numerical evaluation and provide some guidelines for implementing the metric. We also show that TDEC can be measured with both sampling and real-time oscilloscopes provided that there are enough samples for the latter. A comparison of two techniques, one noiseless and one considering noise enhancement, for computing the coefficients of the equalizer is also provided. Finally, an experimental comparison between a Mach–Zehnder modulator and an electroabsorption-modulated-laser-based transmitter is carried out with different extinction ratios and fiber lengths, showing that TDEC can effectively predict the receiver sensitivity penalty.

50G-PON is the next evolution step for ITU-T PON systems beyond 10G that opens up opportunities for new services and applications. This paper reviews the 50G-PON technology itself and different upgrade opportunities for network operators.

In recent years, network operators worldwide have been upgrading their fiber-to-the-home networks from Gigabit-class PON systems to 10G-class. Naturally, the industry has also been working on the next evolution step for PON systems beyond 10G. At the ITU-T, this next step is defined by the Higher-Speed PON systems operating at 50 Gbps line rate. This paper reviews the standardized 50G-PON system and related technologies and what might come next for optical access.

The growing demand for broadband access networks keeps motivating research for higher capacity in both wired and wireless access networks. Recently, the recommendation for 50G-PON with conventional NRZ modulation has been published. Bidirectional point-to-point access networks, also known as BiDi, used in mobile xHaul, are standardized up to 50 Gb/s with PAM-4 as modulation format. The evolution in view of a next generation 6G wireless encourages research towards higher bitrates for fronthaul systems. Hence, there is interest for having single channel BiDi links with a bitrate of at least 100 Gb/s. In this paper we experimentally evaluate four possible IMDD transceiver schemes suitable for optical access applications in the O-Band that can cover BiDi link losses up to a bitrate of 100 Gb/s using PAM-4. We employ an EML with either a 25G-based APD or an optically preamplified p-i-n photodiode (PD) with low-complexity FFE equalization and achieve a real-time power budget of 23.7 dB, just above BiDi B- loss class. By adding an optical booster, we demonstrate up to 34 dB power budget, exceeding with enough margin the highest BiDi class B loss of 25 dB.

We experimentally demonstrate in real-time a 34dB PON power budget, exceeding E1 ODN class, with 100Gb/s PAM4 modulation using an amplified O-Band EML plus receiver-side optical amplification and only low complexity FFE equalization.

A complete suite of 50G-PON standards was finalized by the ITU-T in 2021. The demand drivers for increasing broadband access capacity are reviewed along with the status of ITU-T standardization and prototype technology demonstrations.

A suite of standards Recommendations has recently been developed in the ITU-T for a 50 Gb/s line rate passive optical network (PON) system. This 50G-PON system represents a significant leap in line rate from the 10 Gb/s systems being deployed today in fiber access applications. Achieving such a jump in performance necessitates an evolution in the underlying technologies. The 50G-PON system capitalizes on fundamental advances in the optical transceiver components working in conjunction with enhanced error correction and coding. It also introduces key innovations in activation procedures, contention-based operation, and expanded cryptographic features. With these improved capabilities, the 50G-PON system is ready to meet the new, and demanding, requirements of emerging services.

We evaluate TDEC in a 50G-PON downstream through experiments and show the relation with receiver sensitivity at different fiber lengths and ER. The results show that TDEC effectively follows the penalty induced by transmission impairments.

We perform real-time 50Gb/s transmission targeting the HS-PON standard. An SOA shared at OLT enables 30dB optical budget and 50km upstream burst-mode transmission. The SOA's XGM impact from upstream to downstream is studied. © 2022 The Author(s)

A 100 Gbit/s/ $\lambda $ PAM-4 fiber link with an optical budget of 30 dB and 20 km fiber reach is achieved in real time experiments. This is compliant with class A (20 dB) point to point (PtP) applications as mobile fronthaul for example, and with class N1 (29 dB) point to multipoint (PtMP) for residential market. We used an integrated externally modulated laser, an analog pre-equalizer, an optical booster amplifier and/or non-filtered preamplifier and direct detection without any digital signal processing (whether real-time or offline).

In fiber access, DSP is used for the first time in the ITU-T 50G-PON. Here, we review the benefits of DSP in enabling more flexible PON systems today with 50G-PON and into the future. © 2022 The Author(s)

A monolithically integrated EML+SOA delivering an output power of +13 dBm is demonstrated as a compact Tx for the 50G-PON downstream link. The device delivers +13 dBm of output power with 6 dB extinction ratio and 55 dB/0.1nm OSNR while also passing the 50G-PON eye mask. By exploiting SOA chirp reduction correlated to the gain saturation effects we demonstrate enhanced fiber transmission performance. Since 50G-PON is going to be the first PON technology to adopt digital signal processing (DSP), we use receiver side equalization (EQ) in a 20 km link to demonstrate a link budget of 35.8 dB. Furthermore, working in conjunction with the 50G-PON equalizer, a link up to 40 km SSMF at 1342 nm is realized.

We propose and experimentally validate a novel scheme combining both binary and electrical duobinary detection. At 50Gb/s, in a 1-bit memory channel, we obtain a Rx sensitivity of -25.7dBm with a 25G-class Rx and a low path penalty after 20km using a 1342nm EML Tx.