Overview of high-speed TDM-PON beyond 50 Gbps per wavelength using digital signal processing [Invited Tutorial]

The recent evolution of passive optical network standards and related research activities for physical layer solutions that achieve bit rates well above 10 Gbps per wavelength (lambda) is discussed. We show that the advancement toward 50, 100, and 200 Gbps/lambda will certainly require a strong introduction of advanced digital signal processing (DSP) technologies for linear, and maybe nonlinear, equalization and for forward error correction. We start by reviewing in detail the current standardization activities in the International Telecommunication Union and the Institute of Electrical and Electronics Engineers, and then we present a comparison of the DSP approaches for traditional direct detection solutions and for future coherent detection approaches. (c) 2022 Optica Publishing Grou

Towards Higher Speed Next Generation Passive Optical Networks

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Next generation technologies for 100 Gb/s PON systems

The worldwide explosion of Internet traffic demand is driving the research for innovative solutions in many aspects of the telecommunication world. In access systems, passive optical networks (PONs) are becoming the preferred solution towards which most providers are migrating thanks to the unrivalled bandwidth they can offer. PON systems with a capacity of 100 Gb/s are envisioned as the solution to the dramatic increase in bandwidth and will be essential to support the future fixed and mobile broadband services. However, many challenging aspects have to be addressed in order to overcome the limitations imposed by the physical layer while meeting the economical requirements for mass deployment. In this thesis a comprehensive approach is taken in order to address the most compelling problems and investigate a series of solutions to the current capacity limitations of PONs. Advanced modulation formats are used to achieve bit-rate enhancement from 10 Gb/s to 25 Gb/s re-using the same optoelectronic devices in order to provide a 2.5x increase in transmission speed without resorting to a newer, more expensive generation of higher speed devices. The management of chromatic dispersion is also addressed in order to extend the reach of the networks beyond the standard 20 km using either electronic or optical based compensation strategies. Transmission of 25 Gb/s traffic over fibre lengths of 40 and 50 km is demonstrated confirming the suitability of the proposed technologies for extended reach networks which could greatly reduce the number of existing nodes and hence the capital and operational costs of PONs. Optical amplification strategies are also discussed as a means to improve the physical reach of the networks, both in terms of distance and number of customers. Raman amplifiers and semiconductor optical amplifiers are investigated in order to extend the reach of a PON upstream channel. The results demonstrate a reach of up to 50 km which is more than double the typical fibre length of 20 km adopted in deployed systems today. A number of customers, up to 512, was also demonstrated in a 20 km network, increased from the typical 32 or 64 users of most commercial networks

Key Signal Processing Technologies for High-speed Passive Optical Networks

With emerging technologies such as high-definition video, virtual reality, and cloud computing, bandwidth demand in the access networks is ever-increasing. Passive optical network (PON) has become a promising architecture thanks to its low cost and easy management. IEEE and ITU-T standard organizations have been standardizing the next-generation PON, targeting on increasing the single-channel capacity from 10 Gb/s to 25, 50, and 100 Gb/s as the solution to address the dramatic increase of bandwidth demand. However, since the access network is extremely cost-sensitive, many research problems imposed in the physical layer of PON need to be addressed in a cost-efficient way, which is the primary focus of this thesis. Utilizing the low-cost 10G optics to build up high-speed PON systems is a promising approach, where signal processing techniques are key of importance. Two categories of signal processing techniques have been extensively investigated, namely optical signal processing (OSP) and digital signal processing (DSP). Dispersion-supported equalization (DSE) as a novel OSP scheme is proposed to achieve bit-rate enhancement from 10 Gb/s to 25 Gb/s based on 10G class of optics. Thanks to the bandwidth improved by DSE, the non-return-zero on-off keying which is the simplest modulation format is able to be adopted in the PON system without complex modulation or DSP. Meanwhile, OSP is also proposed to work together with DSP enabling 50G PON while simplifying the DSP complexity. Using both DSE and simple feed-forward equalizer is able to support 50 Gb/s PAM-4 transmission with 10G optics. For C-band 50 Gb/s transmission, injection locking techniques as another OSP approach is proposed to compress the directly modulated laser chirp and increase system bandwidth in the optical domain where a doubled capacity from 25 Gb/s to 50 Gb/s over 20 km fiber can be built on top of 10G optics. For DSP, we investigated the advantages of neural network (NN) on the mitigation of the time-varying nonlinear semiconductor optical amplifier pattern effect. In order to reduce the expense caused by the high computation complexity of NN, a pre- equalizer is introduced at the central office that allows cost sharing for all connected access users. In order to push the PON system line rate to 100 Gb/s, a joint nonlinear Tomlinson- Harashima precoding-Volterra algorithm is proposed to compensate for both linear and nonlinear distortions where 100 Gb/s PAM-4 transmission over 20 km fiber with 15 GHz system bandwidth can be achieved

Optimization of band-limited DSP-aided 25 and 50 Gbps PON using 10G-class DML and APD

The increasing demand for network capacity is driving the development of next-generation high-speed Passive Optical Networks (PON) supporting 25 and 50 Gbps. One solution to reduce transceiver cost is reusing the 10G-class optical transmitter (including Directly Modulated Lasers, DML, in O-band) and receiver components in combination with Digital Signal Processing (DSP) techniques to compensate for bandwidth limitations. In this paper, by means of both a set of laboratory experiments and a metropolitan field demonstrator, we discuss practical PON solutions at 25 and 50 Gbps per wavelength and per direction. In terms of modulation formats, we compare 2-level pulse amplitude modulation (PAM-2), 4-level PAM (PAM-4) and electrical duobinary (EDB) modulation formats, with feed-forward (FFE) and decision-feedback (DFE) adaptive equalizer at the receiver side. The novelty of our paper is manifold. First, we present an optimization in terms of optical receiver band requirements for the 50 Gbps transmission.We show, by means of experimental measurements and numerical simulations, the minimum required bandwidth for DML laser and APD receiver (with appropriate DSP techniques) to realize next generation 25 and 50 Gbps PON transceivers. Second, we discuss also the upstream point of view, with a specific focus on DSP, and in particular, we propose an experimental solution based on a burst mode receiver with memory-aided DSP technique, together with a novel DSP approach to overcome the typical AC coupling distortion due to the burst mode scenario. Finally, we show a coexistence experiment between XGS-PON and 25 Gbps PON on an installed metropolitan field trial

Burst-mode electronic dispersion compensation in long reach PONs

Long reach passive optical networks (LR-PONs), which integrate fibre-to-the-home with metro networks, have been the subject of intensive research in recent years and are considered one of the most promising candidates for the next generation of optical access networks. Such systems ideally have reaches greater than 100km and bit rates of at least 10Gb/s per wavelength in the downstream and upstream directions. Due to the limited equipment sharing that is possible in access networks, the laser transmitters in the terminal units, which are usually the most expensive components, must be as cheap as possible. However, the requirement for low cost is generally incompatible with the need for a transmitter chirp characteristic that is optimised for such long reaches at 10Gb/s, and hence dispersion compensation is required. In this thesis electronic dispersion compensation (EDC) techniques are employed to increase the chromatic dispersion tolerance and to enhance the system performance at the expense of moderate additional implementation complexity. In order to use such EDC in LR-PON architectures, a number of challenges associated with the burst-mode nature of the upstream link need to be overcome. In particular, the EDC must be made adaptive from one burst to the next (burst-mode EDC, or BM-EDC) in time scales on the order of tens to hundreds of nanoseconds. Burst-mode operation of EDC has received little attention to date. The main objective of this thesis is to demonstrate the feasibility of such a concept and to identify the key BM-EDC design parameters required for applications in a 10Gb/s burst-mode link. This is achieved through a combination of simulations and transmission experiments utilising off-line data processing. The research shows that burst-to-burst adaptation can in principle be implemented efficiently, opening the possibility of low overhead, adaptive EDC-enabled burst-mode systems

Adaptive modulation techniques for passive optical networks

Smart use of fiber networks to increase capacity to the hom

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