Optical Network Unit Research Articles

A Dijkstra Based Algorithm for Optimal Splitter Location in Passive Optical Local Area Network (POLAN)

Passive Optical Local Area Networks (POLANs) are integral to modern broadband communication systems, offering high bandwidth and immunity to electromagnetic interference. Designing an efficient POLAN requires careful consideration of splitter placement to minimize network costs. This paper presents an algorithmic approach using Dijkstra's algorithm and the Google Maps API to optimize splitter locations in a POLAN. By treating Optical Network Terminals (ONTs) as nodes in a graph and calculating walking distances between them, the algorithm identifies potential splitter locations that minimize fiber length. Using the Dijkstra's algorithm, the total fiber length used to connect every optical network unit is approximately 274km. Finally, a simulation of the full PON network was carried out and the BER and Q-Factor for each ONU was gotten. An average BER value of 1.8e-11 and Q-Factor value of 13.3 was gotten.

Demonstration of 640 Gbps/160 Gbps WDM-PON system based on colorless ONUs

Abstract The Wavelength Division Multiplexing Passive Optical Network (WDM-PON) is considered a highly promising option for next-generation optical access networks. In this work, we propose and demonstrate a WDM-PON network architecture using colorless Optical Network Units (ONUs). Our design employs a single broadband source (comb source) to generate the optical carriers required for bidirectional transmission. We demonstrate the feasibility of implementing a WDM-PON over a 30 km standard single-mode fiber (SSMF-28), with downstream transmission at 640 Gbps and upstream at 160 Gbps. The proposed method involves comparing two WDM-PON networks with 16 channels, which have similar characteristics. In the first system, we use 32 carriers – 16 for downstream and 16 for upstream – while in the second system, only 16 carriers are used for both directions. In addition, this configuration allows us to easily double the total bandwidth of the network by increasing the number of ONUs to 32 and incorporating the unused carriers (the 16 other unused carriers from the second configuration).

Capacity Optimization of the Next-Generation Passive Optical Networks Based on Genetic Algorithm

This paper proposes an analytical and a numerical models for Next Generation Passive Optical Network (NGPON) by combining Gigabit-PON (GPON) and 10 Gigabit asymmetrical PON (XGPON) technologies. This allows for a larger number of subscribers to be accommodated on the network, up to 256. A capacity optimization procedure based on Genetic Algorithm (GA) techniques is then proposed and analyzed. The uplink and downlink capacities are maximized by optimizing various link parameters, such as the number of Optical Network Units (ONUs), the average optical transmitter power, the receiver sensitivity and the network operating margins. Simulation results shown that, among others, the Distributed-feedback laser (DBF) average power, the Positive-Intrinsic-Negative (PIN) sensitivity and the network margin are the key parameters entrusted to the GA technique in order to maximize the downlink capacity. In contrast, the Fabry Perot (FP) average power, the Avalanche Photodiode (APD) sensitivity and network margin are found to be the most influential parameters optimized by GA to maximize uplink capacity. Significantly, it is demonstrated that the GA technique, when used in optimizing NGPON capacity, enabling 256 subscribers and offering a data rates up to 71.02 Gb/s and 390.56 Gb/s in the upstream and downstream directions, respectively.

Investigation of laser phase noise tolerance in simplified coherent PON with subcarrier multiplexing.

In this paper, we experimentally investigate the laser phase noise tolerance for a 100 Gb/s/λ coherent passive optical network (PON) with simplified optical network units (ONUs) transceivers when distributed feedback (DFB) laser is used as the local oscillator (LO). In the proposed scheme, the digitally subcarrier-multiplexed (DSCM) signals are generated in the coherent transmitter at the optical line terminal (OLT) side based on Alamouti encoding in two polarizations and received by a single-polarization heterodyne receiver at the ONU side. The experimental results show that the power budget can achieve 34.2 dB and 33.9 dB after a 25 km standard single-mode fiber (SSMF) link when external cavity laser (ECL) and DFB lasers are used as the LOs at the ONU side. Polarization and carrier phase tracking schemes for the DSCM systems based on frequency domain pilot tones were used in digital signal process (DSP). At the same time, the frequency offset estimation and phase noise compensation algorithms are conducted using residual carriers. By choosing an appropriate width for the low-pass filter, the optimal performance for the phase noise compensation can be achieved. The pre-equalization operation at the OLT side is also verified for the subcarrier-multiplexed signals to provide better and flatter performances.

Coherent time- and wavelength-division multiplexed point-to-multipoint optical access network using low-cost DFB lasers enabled by a frequency comb.

Coherent reception, along with time- and wavelength-division multiplexing (TWDM), is a promising concept to simultaneously support multiple services in future high-speed point-to-multipoint passive optical networks (PONs). The next-generation PON 2 (NG-PON2) standard describes a TWDM-PON based on IM/DD intensity modulation and direct detection (IM/DD) which employs tunable-lasers and optical filters such as tunable optical filters or cyclic arrayed-waveguide gratings. Here, we investigate what we believe to be a novel coherent TWDM-PON architecture based on a frequency comb source in the optical line terminal (OLT), and thermally-tuned distributed-feedback (DFB) lasers in the optical network units (ONUs). For downstream operation, we broadcast multiple copies of two 25 GBd dual-polarization quadrature phase shift keying (DP-QPSK) signals, resulting in a total PON downstream capacity of 200 Gbit/s. The copies of the downstream signals are spanning ±2 nm (±250 GHz). In the ONUs, we align the wavelengths of the DFB lasers, which act as local oscillators (LOs), to one of the downstream signals by a thermal heater or by changing the direct current. In upstream, the already aligned DFB lasers act as transmit lasers and the frequency comb as LO. We demonstrate TWDM upstream by emulating two ONUs with 25 GBd DP-QPSK, resulting in a total PON upstream capacity of 200 Gbit/s.

Low-latency 100 Gb/s PAM-4 PON with a 42.5 dB power budget over the 20 km anti-resonant hollow-core fiber.

The surging growth in data traffic has necessitated the development of higher-speed, lower-latency intensity modulation and direct detection (IM/DD) passive optical networks (PONs) with higher power budgets. To address the inherent limitations of traditional silica-based solid-core fibers, anti-resonant hollow-core fibers have garnered significant attention from both academia and industry. In this Letter, we present an experimental demonstration of 100 Gb/s PAM-4 IM/DD PON transmission over a 20 km anti-resonant hollow-core fiber in the C band, utilizing low-complexity digital signal processing (DSP). The result achieves a record high power budget of 42.5 dB, facilitated by a 3-tap weighted lookup table (LUT) at the optical line terminal (OLT) side and a semiconductor optical amplifier used as a preamplifier at the optical network unit (ONU) side. This represents the highest power budget reported for IM/DD PON to date, to the best of our knowledge,and offers a promising alternative for the future evolution of PON systems.

Digital pre-equalization for performance improvement in coherent PON

As high-speed optical access networks continue to evolve, reducing the computational complexity at the optical network unit (ONU) side remains a significant challenge in coherent passive optical network (PON). This paper presents a pre-equalization scheme that integrates digital pre-distortion (DPD) and pre-emphasis techniques in 200 Gb/s coherent PON. The focus is on three modulation formats: 50 Gbaud polarization multiplexing-quadrature phase shift keying (PM-QPSK), 50 Gbaud Alamouti-coded polarization multiplexing-16 quadrature amplitude modulation (PM-16QAM), and 25 Gbaud PM-16QAM, using intradyne or heterodyne detection schemes. Through comprehensive numerical simulations and experimental evaluations, we demonstrate significant improvements in receiver sensitivity and power budget in 200 Gb/s coherent PON. When the number of digital filtering taps is small, the proposed scheme achieves power budget enhancements of 3 dB for 50 Gbaud PM-QPSK, 7 dB for 50 Gbaud Alamouti-coded PM-16QAM, and 2.1 dB for 25 Gbaud PM-16QAM in the downlink. These findings highlight the potential of pre-equalization techniques in enhancing the performance of next-generation coherent PON with low computational complexity at the ONU side.

МЕТОД ВИБОРУ ТЕРМІНАЛЬНОГО ОБЛАДНАННЯ ПАСИВНИХ ОПТИЧНИХ МЕРЕЖ НА ОСНОВІ НЕЧІТКОГО БАГАТОКРИТЕРІАЛЬНОГО ПРИЙНЯТТЯ РІШЕНЬ

Currently, optical communication is the dominant technology in cable channels of transport networks, working with powerful homogeneous digital data streams. In particular, the PON (Passive Optical Network) technology is developing dynamically. However, one of the problems holding back PON development is the cost of line and subscriber equipment (Optical line terminal and Optical Network Unit). An urgent task at the moment is the rational choice of equipment when designing optical networks. Most problems in the design of telecommunication networks can be modeled as a multi-criteria decision-making problem, where it is necessary to evaluate several criteria and choose the most acceptable solution option for design engineers according to their preferences and requirements. The article considers the process of selecting an optical line terminal (OLT), which is associated with the evaluation of possible options by a set of indicators. The purpose of the study: building a model of the optimal choice of optical linear terminals in conditions of unclear information. The ambiguity of human judgments when evaluating the importance of criteria (indicators) and evaluating alternatives based on the criteria creates certain problems for decision-makers. The use of fuzzy logic allows processing inaccurate and uncertain information, providing a more complete and accurate assessment of alternatives and evaluation of the importance of criteria. The article proposes the use of fuzzy multi-criteria decision-making methods (Fuzzy MCDM). The Fuzzy SWARA and Fuzzy TOPSIS methods allow you to present an assessment of criteria and alternatives in a descriptive (linguistic) form, which facilitates the decision-making process. In the course of the research, alternatives and criteria for their evaluation were determined, a survey of experts was conducted, evaluations of the degree of importance of criteria and evaluation of alternatives according to criteria were determined. Based on the Fuzzy SWARA and Fuzzy TOPSIS methods, a fuzzy model for selecting an optical line terminal is built. The ranking of the selected optical linear terminals was obtained and the best one was determined.

Bidirectional TFDM 200 G coherent PON with a simplified receiver at the ONU side.

Time and frequency division multiplexing (TFDM) coherent passive optical networks (PONs) are considered as a promising candidate for future optical access networks due to the advantage of high sensitivity, high spectral efficiency, and flexibility. We propose a novel, to our knowledge, bidirectional TFDM 200-Gb/s coherent PON architecture based on the digital subcarrier multiplexing (DSCM) technology. A polarization-insensitive simplified coherent receiver is achieved at the ONU side by Alamouti coding and heterodyne detection. We experimentally demonstrate this bidirectional coherent PON with a 50-Gbaud Alamouti 16 quadrature amplitude modulation (QAM) signal transmitted downstream and a 25-Gbaud dual polarization (DP)-16QAM signal transmitted upstream. By using a single sideband modulated transmitter, only one laser source is required at the optical network unit (ONU) side. The power budgets can reach 30 and 33 dB for the downstream and upstream, respectively, after the 20-km transmission over a standard single-mode fiber (SSMF).

Dynamic ONU grouping algorithm based on combination partition for centralized flexible PON

The traditional optical access network architecture is fixed, and passive optical networking (PON) is only used as the transmission pipeline, which fails to make full use of the exchange capability of OLTs. In this paper, a dynamic optical network unit (ONU) grouping algorithm based on combination partition (DGACP) is proposed in the centralized flexible PON architecture. The algorithm transforms the global partitioning problem into a local partitioning problem, thereby reducing the number of algorithm iterations while obtaining the minimum cross-OLT traffic. Simulation results show that compared with the existing dynamic PON slice restructuring algorithm (DRA), the traffic gain of the DGACP is almost equal or slightly better, and the maximum running time is reduced from around 180 s to less than 0.5 s when the number of ONUs is 512.

Dynamic Bandwidth Slicing in Passive Optical Networks to Empower Federated Learning.

Federated Learning (FL) is a decentralized machine learning method in which individual devices compute local models based on their data. In FL, devices periodically share newly trained updates with the central server, rather than submitting their raw data. The key characteristics of FL, including on-device training and aggregation, make it interesting for many communication domains. Moreover, the potential of new systems facilitating FL in sixth generation (6G) enabled Passive Optical Networks (PON), presents a promising opportunity for integration within this domain. This article focuses on the interaction between FL and PON, exploring approaches for effective bandwidth management, particularly in addressing the complexity introduced by FL traffic. In the PON standard, advanced bandwidth management is proposed by allocating multiple upstream grants utilizing the Dynamic Bandwidth Allocation (DBA) algorithm to be allocated for an Optical Network Unit (ONU). However, there is a lack of research on studying the utilization of multiple grant allocation. In this paper, we address this limitation by introducing a novel DBA approach that efficiently allocates PON bandwidth for FL traffic generation and demonstrates how multiple grants can benefit from the enhanced capacity of implementing PON in carrying out FL flows. Simulations conducted in this study show that the proposed solution outperforms state-of-the-art solutions in several network performance metrics, particularly in reducing upstream delay. This improvement holds great promise for enabling real-time data-intensive services that will be key components of 6G environments. Furthermore, our discussion outlines the potential for the integration of FL and PON as an operational reality capable of supporting 6G networking.

IQ-channel multiplexed DP-4ASK signal using power loading for downlink coherent PON system with access-span length difference

This study explores the integration of dual-polarized (DP) four-level amplitude shift keying (4ASK) signals within an intensity and quadrature division multiplexing framework, mainly focusing on coherent passive optical network (PON) systems. The primary objective is to address the challenges associated with distance disparities in downstream transmissions, which are prevalent in coherent PON architectures. We introduce a novel approach that significantly reduces the power consumption of digital-to-analog converters by implementing power loading strategies tailored explicitly for IQ channel division multiplexing (IQDM)-DP-4ASK signals. Our simulations confirm that ASK standard frequency offset compensation is adaptable to these signals, providing a robust method for managing frequency offsets in a dynamic network environment. Moreover, we propose and empirically validate an energy-efficient adaptive downlink solution capable of supporting 128 Gb/s per optical network unit (ONU), utilizing IQ-imbalanced DP-4ASK signals. This solution is particularly advantageous for systems where the transmission conditions include a 10 km variance in access span lengths between ONUs. Results from our experimental setup demonstrate that reducing the digital-to-analog converter output current for the Q channel by 137 mA is feasible without compromising signal integrity or system performance. Additionally, the research verifies the effectiveness of the automatic bias controller on the transmitter side, ensuring stable operation across varying conditions. Equally, the receiver-side digital signal processing effectively handles polarization separation, illustrating the system's capability to maintain high data integrity and reliability under diverse operational scenarios. These findings highlight the technical feasibility and operational benefits of using IQDM-DP-4ASK signals in coherent PON systems and underscore the potential for significant power savings and enhanced system efficiency in optical networks. The study paves the way for future research into scalable, energy-efficient solutions suitable for high-capacity optical access networks striving for increased sustainability and reduced operational costs.

Benefits of flexibility in current and future IM-DD based TDM-PON [Invited

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.

Performance and energy efficiency enhancement of existing optical communication systems by incorporating resource allocation on demand technique in FiWi networks

Abstract Fiber-wireless (FiWi) networks have begun to be fully integrated into contemporary optical access network systems as a result of utilizing the combined advantages of wired and wireless techniques. Passive optical networks (PON) are heavy energy consumers and one of the main contributors to greenhouse gas emissions (GHG) that are a result of climate change. These systems also present economic challenges. In this work, three different FiWi systems are presented such as (i) even/odd active transmitters with only free space optical (FSO) based optical network units (ONUs)/with dual channel option such as distribution fiber (DF)/FSO supported ONUs, (ii) a novel resource allocation on demand (RAoD) incorporated bidirectional FiWi system supporting DF/FSO based ONUs and four wave mixing (FWM) generated upstream wavelengths and (iii) transmitter diversity enabled 5G supported FiWi system supporting bidirectional communication. It is observed that the energy efficiency of 26.04 % is obtained in even/odd active transmitter and only FSO supported ONUs and under the harsh weather conditions, by adopting DF channel instead of FSO, 30 % energy efficiency further added. However, in novel RAoD technique, energy efficiencies for optical distribution networks (ODN1), ODN2, ODN3, and ODN4 are 48.52 %, 46.4 %, 36.96 %, and 44.31 %. Further, DF option in channel selection improve 30 % more energy saving. In performance enhanced transmitter diversity employed system, at 60 km reduction in bit error rate (BER) are 25 % for ODN1, 5.88 % for ODN2, 20 % for ODN3, and 12.5 % for ODN3.

Design and performance analysis of OAM‐based multidimensional multiplexing RoF‐PON integrated access system

AbstractThe unique advantage of orbital angular momentum (OAM) provides a novel approach to breaking through the limitations of high‐capacity and long‐distance transmission in the conventional radio‐overfiber passive optical network (RoF‐PON) hybrid access network. Introducing the OAM division multiplexing (OAM‐DM) based on Laguerre–Gaussian (LG) beams into the RoF‐PON, an innovative multidimensional system architecture is proposed, which integrates with polarization‐division multiplexing (PDM), wavelength‐division multiplexing (WDM), and orthogonal frequency‐division multiplexing (OFDM) technologies. Successful long‐distance transmission of both the downstream 40 GHz radio OFDM signal and the upstream 40 Gbps on‐off keying (OOK) signal over 80 km are achieved. Additionally, at the optical network unit side, low‐cost upstream carrier re‐modulation technology and flexible access for both wired and wireless signals are realized. The proposed RoF‐OAM‐DM‐PDM‐WDM‐OFDM‐PON architecture offers a dependable solution for high‐capacity and low‐cost future communication systems, holding great importance in achieving flexible access networks.

Positioning multiple optical network units in fiber-wireless networks: An efficient hybrid [formula omitted]-harmonic means clustering approach

Wireless-optical broadband access network (WOBAN) or fiber-wireless (FiWi) is a robust and cost-effective solution to provide high bandwidth network connectivity to mobile subscribers. Optical network unit (ONU) placement is a topological optimization problem that plays a vital role in effective deployment of FiWi network. Recently, some artificial intelligence-based approaches for positioning ONUs were proposed and generated promising results. However, the reported performance in the literature is far from the ideal state. This issue emphasizes the necessity of introducing new placement methods or improving the performance of existing methods. This paper presents a hybrid clustering algorithm for finding the optimal position of multiple ONUs. The proposed backtracking K-harmonic means (BKHM) is an integration of K-harmonic means (KHM) and a backtracking search algorithm (BSA). BKHM not only efficiently specifies the optimal positions of ONUs but also significantly decreases the implementation cost. To demonstrate the performance of the BKHM, we evaluate it on well-known placement benchmarks compared with BSA, KHM, whale optimization algorithm (WOA), enhanced backtracking search (EBS), harris hawks optimization (HHO), and chaotic local search-based levy flight distribution (CLF) algorithms. The experimental results and statistical analysis proved that the proposed BKHM algorithm outperformed its counterparts on most benchmarks in terms of cost optimization, convergence accuracy, and solution quality.

Scheme for a WDM-PON with colorless optical network units based on a flat optical frequency comb.

A new, to the best of our knowledge, scheme for a wavelength division multiplexing passive optical network (WDM-PON) based on a flat optical frequency comb (OFC) is proposed. Using an OFC as the optical source of the system can realize the colorlessness of optical network units (ONUs), and the direct detection of the downlink data further simplifies the ONU structure. The coherent demodulation of the uplink data improves the system performance due to the coherence of the comb lines. In this research, the proposed system is studied for its performance and power budgeting. The results show the flexibility, effectiveness, and practicability of the proposed scheme, which can be applied to future high-capacity optical access networks.

A deep learning based dynamic bandwidth allocation method for XG-PON based mobile fronthaul for CRAN

In the context of 5G and beyond era, the use of Time Division Multiplexed Passive Optical Network (TDM-PON) for mobile fronthaul (MFH) in centralized/cloud radio access network (CRAN) has proven to be an optimal solution for addressing low-latency requirements. While existing literature has predominantly focused on optimizing mobile fronthaul latency rather than end-to-end latency, this paper introduces an end-to-end latency model for TDM-PON, specifically within a 10-gigabit Passive Optical Network (XG-PON) based MFH for CRAN. The paper then proposes an Intelligent Dynamic Bandwidth Allocation (DBA) scheme to minimize end-to-end latency of the network. The proposed scheme predicts the buffer occupancy reports using deep learning techniques at optical network units (ONUs). Thereafter, optical line terminal (OLT) schedules the available bandwidth using conventional DBA schemes (Group-GIANT i.e., Ggiant, Optimized Round Robin, Dynamic Service Interval). Primarily, the proposed DBA scheme transforms conventional DBA schemes (Ggiant, Optimized Round Robin, Dynamic Service Interval) into Intelligent versions (Intelligent Ggiant, Intelligent ORR, Intelligent DSI), showcasing a reduction of 28.63 %, 45.86 %, and 48.60 % in end-to-end latency in the XG-PON-based MFH for CRAN. Further, the analysis of obtained results has confirmed the supremacy of the Intelligent DSI DBA scheme over the Intelligent Ggiant and the Intelligent ORR DBA scheme.

Simplified coherent optical network units for very-high-speed passive optical networks

Future passive optical networks (PONs) for 200Gb/s/λ, and beyond, pose a significant technological challenge. The use of coherent technology in access networks provides a great solution based on concepts from mature technologies to achieve the speeds needed for very-high-speed PON (VHSP). In this paper, we provide an overview of the currently demonstrated technologies and propose a possible simplified optical network unit (ONU) for time division multiplex PON (TDM-PON). The proposed ONU uses a single polarization heterodyne receiver, using either a balanced photodiode or a single-ended one and an electro-absorption modulated laser (EML)-based transmitter. The experimental demonstration using the proposed ONU in a bidirectional, symmetrical transmission over fiber distances of 20 km and 40 km shows the viability of the technology. The downstream direction achieves a power budget of 34.3/29.3 dB for 20 km and 33.9/29 dB for 40 km, for a balanced/single-ended receiver, whereas the upstream transmission achieves 29.3 dB for both scenarios.

Enhanced authentication technology based on deep neural network in the physical layer of optical communication

To solve the problem of device identity security management in Passive Optical Networks (PON), this study proposes an enhanced authentication technique based on Deep Neural Network (DNN) in the physical layer of optical communication. By negotiating the device power and transmission distance used with legitimate Optical Network Units (ONUs), the Optical Line Terminal (OLT) can obtain a unique channel feature fingerprint for each legitimate device. These features are then identified and classified using a trained Deep Neural Network. Also, the method takes into account the substitution and fiber-splitting interception attacks. Simulation results show that the legitimate devices can be accurately identified using 64 neurons and 20 iterations, with a recognition accuracy of 100 %. Therefore, the method effectively improves the ability of the PON system to resist spoofing attacks at the physical layer and significantly improves the security level of the system.