This paper demonstrates the feasibility of AI-based ODN monitoring for upstream sensing in IM/DD PONs using polarization sensing. A multi-user upstream PON scenario validates classification/localization accuracy of up to 99.98% in a proof-of-concept setup.

This paper presents the advances and challenges of design, integration, and performance evaluation of a space-division multiplexing passive optical network (SDM-PON) system based on newly developed 7-core weakly-coupled multicore fiber (WC-MCF). A long-wavelength vertical cavity surface emitting laser (VCSEL) array, customized for O-band operation, was developed and experimentally characterized. To address optical alignment challenges, both expanded beam coupling and adaptive coupling using spatial light modulators were examined. Meanwhile, experimental results under low-crosstalk conditions demonstrated that simplified single-input-single-output (SISO) digital signal processing (DSP) offers comparable performance to multiple-input-multiple-output (MIMO) DSP in the proposed SDM transmission system, enabling reduced complexity and power consumption. Our proposed SDM-PON architecture also delivers performance comparable to standard single-mode fiber (SMF) configurations, with the potential for increased capacity and reduced fiber deployment costs. The scope is then broadened to investigate the scalability of general WC-MCF-based SDM links toward higher core counts. The study also mentioned key design trade-offs and technical challenges at the device and system levels, including limitations in VCSEL bandwidth, coupling efficiency and laser chirp. Overall, the proposed SDM-PON architecture demonstrates strong potential for cost-effective and energy-efficient deployment in future access networks.

With the steadily progressing digitization of our society and the migration into urban areas, digitized and highly connected smart cities have attracted much attention from the research community due to their impact on everyday life, potential for new innovations, and ability to reduce carbon footprints. The versatile applications, which are intended to improve life in cities in various aspects, have one thing in common—they rely on widespread, reliable, and high-performing communication networks. Therefore, optical-access networks will be a crucial part of the smart cities’ network infrastructure as they provide cost-effective and high-speed connectivity to antenna sites, residents, enterprises, businesses, and regional data centers in a point-to-multipoint topology. In this article, we address the overall impact of this urban transformation on such networks. We outline our vision of the future smart sustainable city, which will leverage advanced optical-access networks. Subsequently, the physical layer design of optical-access networks is analyzed in the context of point-to-multipoint network topology. This includes a 100-Gbit/s intensity-modulation and direct-detection passive optical network (PON) and a 200-Gbit/s coherent PON utilizing eight-digital subcarrier-based time- and wavelength-division multiplexing and coherent detection. We discuss artificial intelligence-based network monitoring and resource allocation. Next, we provide a techno-economical study for sustainable fiber deployment strategies. Finally, we report the results of a network demonstration for the remote assistance of a connected autonomous vehicle.

The concept of performing Distributed Acoustic Sensing (DAS) on a field-deployed 25G PON network was experimentally verified. Various use cases to sense the optical distribution network behind the splitter were demonstrated and analyzed during a Field Trial at municipal utilities Sindelfingen, Germany. (c) 2025 The Author(s)

We experimentally demonstrate a novel blind LO-locking technique for 224 Gbit/s coherent PON downstream that is applied during ONU startup and allows using wavelength uncalibrated LO lasers in the ONU module.

We discuss the perspectives of fiber-optic sensing in the case of passive optical networks (PON). We address PONspecific challenges such as the point-to-multipoint topology, cost constraints, and adaptation of existing monitoring techniques to intensity modulation. We then propose a possible PON monitoring architecture.

We present North American operator trial involving world’s first simultaneous operation of four PON technologies: 100G-PON, 50G-PON, 25GS-PON and XGS-PON over a field-deployed 11-km-long fiber. We report correct operation of all systems in the trial.

We perform a live demo of 100G NRZ-OOK PON downstream coexisting with XGS and 25GS PON over field-deployed fiber in Australia. We achieve a loss budget of >31 dB using pre-amplified reception, advanced equalization, and soft-input FEC decoding.

We experimentally demonstrate a bidirectional 240Gbit/s coherent PON with a novel blind wavelength alignment technique that is applied to both ONU lasers during ONU startup. The proposed technique allows using cost-effective wavelength-uncalibrated lasers in the coherent ONU. (c) 2025 The Author(s)

This conceptual study investigates the potential use of mono-optics concept transceivers for Fiber in-Premises applications. Advantages and challenges are highlighted and discussed. First measurements confirm the feasibility of this approach. (c) 2025 The Author(s)

We demonstrate an optically-powered acoustic sensor module, located along a 123-km Raman-amplified 31 x 400 Gb/s DWDM link. Residual Raman pump light both powers the sensor module and serves as the optical carrier for transmitting acoustic signals. (c) 2025 The Author(s)

We demonstrate a novel scheme and configuration that allows commercial TDM-PON systems to support 802.1CCB-FRER for enhanced reliability in TSN. We experimentally evaluate and compare the performance of 802.1CB-FRER traffic flow and normal (non-FRER) traffic flow co-existing in the same TDM-PON infrastructure in case of link-fault. .

Passive optical networks (PONs) facilitate small-cell deployments. Back- and midhaul over PON is being deployed today. As opposed to point-to-point optics, PON extends the aggregation gain into the access domain. We explain the steps taken in the mobile and PON industries to enable efficient eCPRI fronthaul over PON. We explain how fronthaul has evolved into a bandwidth-efficient eCPRI and what mechanisms are in place to enable coordinated scheduling decisions of the mobile and PON systems. The recent end-to-end demonstration of coordinated scheduling helps pave the way towards future industry adoption.

Due to continuously emerging high bandwidth applications, research and standardization of time division multiplexed passive optical networks (TDM-PONs) have focused on increasing the peak bitrate. However, increasing the bitrate while supporting the stringent optical power budget of a PON becomes increasingly challenging because of the larger chromatic dispersion penalties as well as reduced receiver sensitivity when the bitrate of the intensity modulation with direct-detection (IM-DD) based PON is increased. Also, increasing bitrate generally causes higher power consumption, which leads to more challenging thermal designs and misalignment with environmental targets. In this paper we give an overview of flexible concepts that can help achieve the required optical power budget and support reduced power consumption of a future IM-DD based TDM-PON. We demonstrate that a flexible PON can provide an increased overall throughput or an extended reach and power budget with the use of flexible modulation formats, probabilistic and geometric shaping, and flexible rate forward error correction (FEC). Another dimension of flexibility in the form of a configurable optical distribution network (ODN) is described and its merits and challenges are discussed. Flexible concepts based on interleaving of FEC codewords can align signal processing like FEC decoding and the protocol processing closer to the user-rate of an optical network unit (ONU), which leads to reduced power consumption. Flexibility based on multiple channels based on wavelength multiplexing or spatial multiplexing enables optimization of the power consumption to the amount of traffic on the PON. Several flexible concepts have already been adopted in the PON standards. We highlight flexible gain FEC for upstream 50G PON, the transmitter dispersion eye closure (TDEC) metric, and the flexible split-ratio ODN for power saving. Flexible modulation has not been adopted yet in PON standards, but it is expected that flexibility is more and more needed to support the performance, cost effectiveness, and power conservation of future optical access systems.

An ML-supported diagnostics concept is introduced and demonstrated to detect and classify events on OTDR traces for application on a PON optical distribution network. We can also associate events with ODN branches by using deployment data of the PON. We analyze an ensemble classifier and neural networks, the usage of synthetic OTDR-like traces, and measured data for training. In our proof-of-concept, we show a precision of 98% and recall of 95% using an ensemble classifier on measured OTDR traces and a successful mapping to ODN branches or groups of branches. For emulated data, we achieve an average precision of 70% and an average recall of 91%.

We demonstrate a 50G-PON upstream SOA-UTC based receiver integrated with a BM-TIA, without optical filtering. The OMA sensitivity is -24.3 dBm, the dynamic range exceeds 20 dB and the loud-soft penalty is 1 dB.

Passive optical networks (PONs) facilitate small cell deployments. Back- and midhaul already make efficient use of PON. We explain the steps taken in mobile and in PON industries to enable efficient eCPRI fronthaul over PON.

Next-generation passive optical networks (PONs) with upstream rates of 50 Gbit/s and beyond will require a new class of burst-mode transimpedance amplifiers (BMTIAs) that are linear to enable (digital) equalization of channel impairments. Such linear BMTIAs also enable higher-order modulation formats like 4-level pulse amplitude modulation (PAM-4). In this paper, we demonstrate operation of a novel linear BMTIA integrated together with a commercial off-the-shelf 25G-class avalanche photodiode (APD), achieving 50 Gbit/s non-return-to-zero (NRZ) operation with a sensitivity of −23.7 dBm optical modulation amplitude (OMA) and dynamic range exceeding 21.7 dB and 100 Gbit/s PAM-4 operation with a sensitivity of −15.8 dBm OMA and dynamic range exceeding 15.4 dB, both at a bit error ratio (BER) of $10^{-2}$ . In addition, fast burst-mode gain-control and balancing circuits limit loud-soft sensitivity penalties in the case of AC-coupled circuits to less than 1.3 dB. The chip was designed in a 0.13 $\mu$ m SiGe:C BiCMOS technology, has an area of 1.2 × 1.7 mm $^{2}$ and consumes between 260 mW and 310 mW. This receiver paves the way to a next-generation class of BMTIAs, supporting the ITU-T G.9804.3 Amd 1 standard.

We propose, analyze, and experimentally verify the effectiveness of combining flexible-rate passive optical networks with power-adjustable splitters for enhancing user throughput. We demonstrate the possibility of increasing the fraction of users capable of supporting PAM4 by more than 100% in an exemplary optical distribution network.

We demonstrate operation of a linear burst-mode TIA integrated with a commercial lensed APD supporting 100-Gbit/s PAM-4 with OMA sensitivity of −15.8-dBm and 50-Gbit/s NRZ with OMA sensitivity of −23.7-dBm. Dynamic range exceeding 21.7-dB is achieved for NRZ and 15.4-dB for PAM-4 reception.