Passive Optical Network System Research Articles

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.

End-to-end learning of joint noise shaping and probabilistic shaping for OAM mode division multiplexing transmission.

Intensity modulation direct detection (IM/DD) orbital angular momentum (OAM) mode division multiplexing (MDM) technology can greatly expand the capacity of a communication system, which is a promising solution for the next generation of high-speed passive optical networks (PONs). However, there are serious obstacles such as mode coupling, device nonlinear impairment, and quantization noise in an IM/DD OAM-MDM system with a low-resolution digital-to-analog converter (DAC). In this Letter, we propose a novel, to the best of our knowledge, end-to-end (E2E) learning scheme based on a double residual feature decoupling network (DRFDnet) emulator with joint probabilistic shaping (PS) and noise shaping (NS) for the OAM-MDM IM/DD transmission. Our DRFDnet emulator can accurately build a complex nonlinear model of an OAM-MDM system by separating the signal impairments into linear and nonlinear. Meanwhile, a DRFDnet-based E2E scheme for joint PS and NS is presented with the aim of compensating the signal impairment for the OAM-MDM IM/DD system. An experiment is carried out on a 200 Gbit/s PON system based on the OAM-MDM IM/DD transmission. The experimental results demonstrate that the proposed DRFDnet-based joint PS and NS scheme is a promising solution to effectively mitigate nonlinear distortions and outperforms the CGAN-based joint PS and NS scheme and traditional joint PS and NS scheme with receiver sensitivity improvements of 1.2 dBm and 2.5 dBm under hard-decision forward error correction (HD-FEC) thresholds, respectively. Our experimental results demonstrate that the proposed DRFDnet emulator-based E2E learning scheme is a viable candidate for future PON.

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.

Investigation of 16 × 10 Gbps mode division multiplexed enabled integrated NGPON–FSO architecture under wired-wireless link losses

Abstract To enhance the transmission capacity for energy consumption and low cost system, mode division multiplexing (MDM) using mode 0 and mode 1 is proposed and investigated. A pair of eight downlink and uplink wavelengths is transmitted by using each MDM mode in an integrated bidirectional next generation passive optical network and free space optics (NGPON–FSO) system at 10 Gbps per channel transmission rate under the impact of FSO–fiber links impairments. Simulation results indicate that received power of −21.2 dBm with 0.2 dB power penalty can be obtained over 1 km FSO and 100 m multimode fiber under unfavourable turbulent effects. The system provides extended FSO link range, and fiber range of 150 km and 600 m respectively at threshold limit of 10−3. Besides, the mathematical analysis depicts the receiver sensitivity and splitter power budget of 42 dBm and 18 dB, respectively, for the proposed system. The system offers finest performance than other pre-existing systems.

Client scheduling and bandwidth slicing for multiple federated learning tasks over multiple passive optical networks

Federated Learning (FL) has attracted extensive attention in facilitating emerging edge intelligence applications for its inherent advantages of ensuring data security and privacy. Especially in the edge computing networks connected by Passive Optical Network (PON) system, FL is introduced to enable applications like autonomous driving, intelligent manufacturing, and precision medicine. However, in this system, the FL deployment over PON inevitably faces challenges induced by the conflict between a large volume of model data with the restrict latency limitation and the confined bandwidth resource of PON, especially for the multiple FL tasks. To address these issues, a novel scheme is proposed for tackling the client distribution and bandwidth allocation problems under the scenario of multiple simultaneous FL tasks supported by the multiple interconnected PON systems, which is consisted of the client scheduling and bandwidth slicing processes. To be specific, an easy-to-implement heuristic algorithm is first performed to assign the client numbers to PONs based on iterative method, with which certain operations are repetitively executed to achieve optimal solutions. And then, the serial bandwidth slicing which adapts the traditional policy, i.e., one-task-per-cycle, to the situation with multiple FL tasks, and parallel slicing with the multi-task-per-cycle, are designed for the investigated system. Furthermore, the simulation system is constructed to verify our method. The corresponding results exhibit that, the largest 43.2 % round time reduction is achieved by client scheduling compared to benchmark without the scheduling. Compared to the benchmark with serial slicing, our scheme can achieve a maximum 50.11 % of the round time decrease. It's also validated that, our proposed client scheduling and parallel bandwidth slicing method can improve the learning efficiency by reducing communication delay, especially for the situation with less client number and smaller FL threshold.

Enhanced PON and AMCC Joint Transmission with GMM-Based Probability Shaping Techniques

In ITU-T standards, auxiliary management and control channels (AMCCs), as defined, facilitate the rapid deployment and efficient management of wavelength division multiplexing passive optical network (WDM-PON) systems. The super-imposition of an AMCC introduces additional interference to a PON signal, resulting in the degradation of the performance of the overall transmission. In prior research, we proposed employing a Gaussian mixture model (GMM) to fit a baseband-modulated AMCC signal. Following the analysis of the interference model and the distribution characteristics of received signal errors, we propose a combined optimization method for a transmitter and receiver in this paper. This method, grounded in probabilistic shaping (PS) techniques, optimizes the probability distribution of the transmitted signal based on the AMCC interference model, with the objective of reducing the error rate in PON signal transmission. We have validated this approach within a 50G-PON experimental system by utilizing PAM4 modulation. The experimental results demonstrate the effectiveness of this method for mitigating the impact of baseband-modulated AMCC, thereby reducing the error rate in PON signal transmission. The approach presented in this paper can further minimize the performance degradation introduced by baseband-modulated AMCC in WDM-PON systems, enhancing the efficiency of WDM-PON deployment.

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.

Efficient transport of enhanced CPRI fronthaul over PON [Invited

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.

Design and Anti-Interference Analysis of Fault Monitoring System Based on Multi-Wavelength Grouping for Passive Optical Network System

Design and Anti-Interference Analysis of Fault Monitoring System Based on Multi-Wavelength Grouping for Passive Optical Network System

Auxiliary Management and Control Channel Transmission and Performance of High-Speed Coherent Frequency Division Multiplexing Passive Optical Network System

Auxiliary Management and Control Channel Transmission and Performance of High-Speed Coherent Frequency Division Multiplexing Passive Optical Network System

Coexistence in future optical access networks from an operator’s perspective [Invited

In this paper, we address the challenges related to the simultaneous operation of legacy and future network technologies in passive optical networks (PONs) and point-to-point topologies. We explore the coexistence issues for various user categories, including residential, enterprise, factories, and mobile users. The future access networks will need to accommodate multiple technologies concurrently. Our paper demonstrates how G-PON, XGS-PON, and 50G-PON can coexist on the same optical distribution network using triple coexistence multi-PON modules. However, there are certain limitations that need to be considered, such as achieving a high optical budget and the associated costs, both in terms of monetary investment and CO2 emissions for technology deployment by operators. Additionally, we emphasize the significance of optical line terminals (OLTs) as crucial network components in the future. OLTs play a central role in supporting the traffic evolution with optimal efficiency in terms of throughput, latency, jitter, and adherence to CO2 emission constraints. Finally, we experimentally demonstrate the first assessment, to our knowledge, of a 50G-PON prototype with optical budget reaching 23.9 dB limited by the downstream (DS). Furthermore, we evaluate the potential limitations regarding coexistence by examining the effects of stimulated Raman scattering between the DS of 50G-PON and the upstream of XGS-PON for the first time with real PON systems.

Development of a cost-effective optical network based on free space optical (FSO) and optical fiber links for enabling smart city infrastructure: A hybrid approach

Due to the gigantic rise in the use of high data rate-based applications and the ongoing transformation of Indian cities into smart cities, there is a need for a high-speed communication framework to handle the enormous data traffic. The radio frequency (RF) and microwave links seem to be incapable of offering sufficient bandwidth required by the data-hungry applications and consequently, the need for a more effective solution for tackling the issue of scarcity of bandwidth resources has become the necessity of current network infrastructure in India. In this study, a hybrid optical fiber-free space optical (OF-FSO) system for offering high-speed data services has been proposed to assist the implementation of smart city infrastructure in India. This study aims to inspect the system performance of the proposed model under the climatic conditions of mountainous, desert, flatland, and seaside regions of India. The proposed hybrid OF-FSO system comprises a fixed single-mode fiber (SMF) of 20 km and an FSO link (having a varied transmission range between 0–2 km). The proposed hybrid model can support an FSO link of 1.72 km for a fixed SMF of 20 km, corresponding to a bit error rate of the order of 10−4 for atmospheric conditions of the seaside location of Chennai and the range of FSO link varies from 1.32 km to 1.57 km for other locations of India, for the same length of SMF and bit error rate. Furthermore, the proposed hybrid OF-FSO has demonstrated a reduction of 30.8% in Capital Expenditure (CAPEX) cost in contrast to the conventional passive optical network (PON) system.

Development and verification of an on-board integrated optics scheme for a 50G/10G combo PON system

We propose an on-board integrated optics (OBO) scheme within a 50G/10G combo passive optical network (PON) system, for the first time to our best knowledge, which can achieve high port density, low cost, and low power consumption required by the 50G PON system. We provide an OBO scheme that integrates record-high power distributed feedback (DFB) lasers, low insertion loss silicon modulators, a planar lightwave circuit wavelength-division multiplexer, and avalanche photodiodes on a single board, which can solve key issues faced by the demand of coexistence and smooth evolution from 10G to 50G PON for global access network operators. In this system, the slope efficiency of the lasers has been optimized at high temperatures, allowing the output power of the lasers to achieve a record-breaking 23.5 dBm at 1577 and 1342 nm, while reducing cooling power consumption to realize low carbon emission in access networks. We developed a low-loss broadband silicon modulator to meet the large power budget and high data rate requirements of 50G PON by optimizing doping parameters and constructing electrodes that match the driver. This silicon modulator has a 6.6 dB insertion loss and an electro-optic bandwidth of more than 38 GHz, making it the ideal silicon modulator for 50G PON systems. In addition, we verify the end-to-end performance, including receiver sensitivity in the upstream direction and the dispersion penalty in the downstream direction. This suggests that the OBO scheme can satisfy the criteria of the 50G PON system according to the ITU-T G.9804 standard series.

Flexible PON systems enabling optical virtual private network and upstream channel upgrade

With the rapid growth of peer-to-peer (P2P) traffic in the access network, the capability to implement inter-optical network unit (ONU) communication (IOC) has become a fundamental requirement for the underlying passive optical network (PON). The conventional IOC is realized electronically on layer 2 or layer 3 and relies on the transfer operations in the optical line terminal (OLT), thus resulting in high transmission latency and excessive bandwidth consumption. To achieve an efficient IOC, the optical virtual private network (OVPN) is proposed to establish direct optical layer links among ONUs by adding some auxiliary optical components to the existing PON system. However, in previously reported OVPN schemes, the added devices are only used for IOC and cannot fulfill other network functions, which leads to poor flexibility. To improve the reconfigurability of the whole PON system, we present two simple modifications that can not only achieve a high-bandwidth OVPN but also increase the upstream channel capacity. The proposed schemes introduce a new wavelength as the OVPN channel to refrain from changing the physical configuration of the normal upstream and downstream. One scheme retrofits the optical line terminal (OLT) with a fiber Bragg grating (FBG) based reflection module, while the other employs an additional short-length distribution fiber for each ONU to redirect IOC traffic. In both schemes, optical switches (OSWs) are used to control the added OVPN wavelength and the original upstream wavelength so that the two wavelengths can transmit IOC traffic and upstream traffic flexibly. According to the states of OSWs, PON systems will form multiple working modes adapted to different network conditions. To evaluate the improvement in flexibility of wavelength usage, the throughput performances of proposed schemes were analyzed theoretically under varying offered loads and IOC traffic proportions. In addition, the feasibility of both schemes was verified through physical layer simulations, where the optical spectra and bit error rates (BERs) of signals on different wavelengths were investigated.

Improved passive optical network RoF system based vertical cavity-surface emitting laser (VCSEL) optical source external modulation

Passive Optical Network (PON) is a promising 5 G optical fiber network technology, that can enhance reliability data rate, and bandwidth saving. This simulation-based study investigates the feasibility of implementing a vertical cavity-surface emitting laser (VCSEL) optical source along with wavelength-division multiplexing (WDM) for designing a PON radio over fiber (RoF) system that can authorize multi-subscribers, users, to simultaneously use the same optical fiber for Front long-haul data transmission. Three scenarios are proposed: First, a VCSEL, and a Mach–Zehnder Modulator with a distinctive frequency are made accessible to every user in the PON system. Whereas, in the second scenario, a continuous wave (CW) laser is used to replace the VCSEL in the same PON. 16 users are multiplexed by a WDM and transmitted over a link length of 200 km. The system performance is, thus measured in terms of Q-factor, and it is revealed that the VCSEL-based system outperforms the system utilized CW laser to a distance of 150 km, with a maximum gain in the Q-factor of about 4.5. Both postulated systems are able to achieve a maximum transmission distance of 180 km with a minimum Q-factor of 6. Moreover, to minimize, the input current of around 1 mA and the system complexity, a third scenario is presented in which one VCSEL with 193.1 THz is shared among multiple users. The Q-factor performance is then simulated for up to 72 users, revealing that the minimum level of acceptable Q-factor has been maintained up to a link length of 180 km.

Investigation of 2.24Tbps full-duplex integrated multi-beam FSO/MDM-next generation PON under diverse atmospheric conditions

A full-duplex 2.24Tbps mode division multiplexing (MDM) based integrated multi-beam free space optics (FSO) and next generation passive optical network (NGPON) system to mitigate the atmospheric turbulence and fiber dispersion with enhanced network scalability as well as efficiency is proposed. In emergency scenarios the utilization of polarization shift keying (PolSK) and dual polarization (DP)-differential quadrature phase-shift keying (DQPSK) modulation in system offers high spectral efficiency, coherent detection, minimum link dispersion and less noise. The simulation results demonstrate the faithful MDM-FSO/NGPON signals transmission over 40 km fiber with 500 m multi-beam FSO links at −8 dBm received power and 2 dB maximum power penalty. Also, the maximum fiber & FSO range can be expanded upto 160 km and 1500 m respectively, considering fiber impairments and diverse weather conditions. The system also supports simultaneous 200 end users having 23–47 dB total channel loss. High optical to signal noise ratio of 36 dB in downlink and 44 dB in uplink is acquired successfully. The comparison of the designed system with other systems signifies its superiority to others.

Artificial Neural Network Assisted Probabilistic and Geometric Shaping for Flexible Rate High-Speed PONs

In this paper, we employ artificial neural networks (ANNs) to optimize joint probabilistic shaping (PS) and geometric shaping (GS) for a realistic 50G IM/DD passive optical network (PON) link. Apart from being able to find a generalized mutual information (GMI)-maximizing modulation for channel conditions unseen at the training phase, the compatibility of the ANN training with Monte Carlo simulation also enables us to use a more complicated channel model that more closely resembles a real PON system where fiber dispersion, bandwidth limitation and digital signal processing (DSP) are present. The forward error correction (FEC) requirement that must be satisfied in an actual implementation is imposed on the learned modulation by including a normalized GMI (NGMI) penalty term in the loss function. The proposed scheme is demonstrated with simulations. Results show that the ANN can achieve similar performance compared to a case-by-case optimization while also being capable of generalizing to a wide range of received optical power (ROP) from −30 dBm to −18 dBm and/or a broad range of fiber distance from 0 km to 20 km. About 0.1-bits/symbol GMI improvement is attained compared to uniform modulation.

Design of time division multiplexing/wavelength division multiplexing passive optical network system for high-capacity network

This paper presents the design of time division multiplexing-wavelength division multiplexing-passive optical network (TDM-WDM PON). In this design, the current TDM PON is incorporated with the proposed WDM-PON in order to design a high-capacity network with lower loss requirements. The design has been simulated using OptiSystem software. The upstream wavelength for WDM is between 1,530.334 to 1,542.142 nm while for TDM is 1,310 nm. The downstream wavelength for WDM is from 1,569.865 to 1,581.973 nm, while for TDM is 1,490 nm. Based on the result, it is found that the proposed network is capable to support up to 64 customers with a bit rate of 2.5 Gbps.

Performance investigation of contention and monitoring in long-reach passive optical networks

Abstract Optical fibers are a key inventive discovery that contributed to the digital revolution, although cost becomes a major factor for long-distance communication. Whereas passive optical networks (PONs) offer reduced costs and cater to multiple users; hence, they are becoming more common in LANs, densely inhabited areas, and backbone networks. Numerous experiments on PON systems have been authored in the last couple of years, with results expressed in terms of BER, eye openings, quality of received bits factor, signal-to-noise ratio (SNR), and burst blocking, which demands a vast review of PONs based on these parameters. So, a comprehensive review of PONs is extensively researched to identify the methods’ limitations. Along with long-reach(LR)-PON systems, power conservation in PONs and burst contention are also addressed. To demonstrate the performance of PON architectures, the findings are provided in terms of delay, energy efficiency, and operations intensity.

Simultaneous enhancement of the bandwidth and responsivity in high-speed avalanche photodiodes with an optimized flip-chip bonding package.

The enhancement in responsivity of photodiodes (PDs) or avalanche photodiodes (APDs) with the traditional flip-chip bonding package usually comes at the expense of degradation in the optical-to-electrical (O-E) bandwidth due to the increase of parasitic capacitance. In this work, we demonstrate backside-illuminated In0.52Al0.48As based APDs with novel flip-chip bonding packaging designed to relax this fundamental trade-off. The inductance induced peak in the measured O-E frequency response of these well-designed and well-packaged APDs, which can be observed around its 3-dB bandwidth (∼30 GHz), effectively widens the bandwidth and becomes more pronounced when the active diameter of the APD is aggressively downscaled to as small as 3 µm. With a typical active window diameter of 14 µm, large enough for alignment tolerance and low optical coupling loss, the packaged APD exhibits a moderate damping O-E frequency response with a bandwidth (36 vs. 31 GHz) and responsivity (3.4 vs. 2.3 A/W) superior to those of top-illuminated reference sample under 0.9 Vbr operation, to attain a high millimeter wave output power (0 dBm at 40 GHz) and output current (12.5 mA at +8.8 dBm optical power). The excellent static and dynamic performance of this design open up new possibilities to further improve the sensitivity at the receiver-end of the next-generation of passive optical network (PON) and coherent communication systems.