Key Signal Processing Technologies for High-speed Passive Optical Networks
Doktorsavhandling, 2021

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.

neural network

passive optical network

optical signal processing

digital signal processing

dispersion supported equalization

Optical access network

semiconductor optical amplifier

Room EC, Hörsalsvägen 11, 5th floor, Chalmers University of Technology, Johanneberg campus, and Via Zoom
Opponent: Dora van Veen, Nokia Bell Labs, USA


Lei Xue

Chalmers, Elektroteknik, Kommunikation, Antenner och Optiska Nätverk

L. Xue, L. Yi, H. Ji, P. Li, and W. Hu, First demonstration of symmetric100G-PON in O-band with 10G-class optical devices enabled by dispersion-supported equalization, Optical Fiber Communication Conference and Exhibition (OFC), paper M3H.1, Los Angeles, USA, 2017.

L. Xue, L. Yi, H. Ji, P. Li, and W. Hu, Symmetric 100-Gb/s TWDM-PON based on 10G-Class optical devices enabled by dispersion-supported equalization, Journal of Lightwave Technology, vol. 36, no. 2, pp. 580–586, 2018.

L. Xue, L. Yi, H. Ji, Z. Li, and W. Hu, First real-time demonstration of symmetric 100G-PON, Asia Communications and Photonics Conference and Exhibition(ACP), paper AS4A.3, Wuhan, China, 2016.

100G PAM-4 PON with 34 dB Power Budget Using Joint Nonlinear Tomlinson-Harashima Precoding and Volterra Equalization

European Conference on Optical Communication, ECOC,; (2021)

Paper i proceeding

SOA pattern effect mitigation by neural network based pre-equalizer for 50G PON

Optics Express,; Vol. 29(2021)p. 24714-24722

Artikel i vetenskaplig tidskrift

L. Xue, L. Yi, P. Li, and W. Hu, 50-Gb/s TDM-PON based on 10G-class devices by optics-simplified DSP, Optical Fiber Communication Conference and Exhibition(OFC), paper M2B.4, San Diego, USA, 2018.

Optics-simplified DSP for 50 Gb/s PON downstream transmission using 10 Gb/s optical devices

Journal of Lightwave Technology,; Vol. 38(2020)p. 583-589

Artikel i vetenskaplig tidskrift

50-Gb/S Dispersion-Unmanaged DMT Transmission with Injection Locked L0G-Class L.55-μm DML

2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings,; (2019)

Paper i proceeding

50-Gb/s Dispersion-unmanaged DMT Transmission with Injection Locked 10G-class 1.55-mu m DML

Optics InfoBase Conference Papers,; (2019)

Paper i proceeding

Passive optical access networks go a long way. Nowadays, we use bandwidth for everything. We use it for online shopping, work, and watching TV at home. We also use it for video conferences and chatting with friends through wi-fi in a cafe. In order to provide these ultra-broadband services at any time and anywhere they are needed, optical access networks with very high throughput are required. The optical access networks are the fiber optic links that connect the network equipment at the user's side to the operator’s network. It is very close to the user, so the network is cost-sensitive. Large-scale optical access networks adopt passive optical networks (PONs) due to the corresponding point-to-multipoint network architecture. In such architecture, a single fiber connects the operator’s network and the user side, and when it gets close to areas with a dense number of users, a passive splitter rather than an active switch (need power supply) is used to connect the subscriber side over a short distance. So it enables maximum fiber sharing and the lowest installation, operation, and management costs. PONs can transmit gigabytes of data per second now, and the demand for higher capacity is increasing due to the emerging bandwidth-consuming services, e.g., virtual reality. Reusing legacy optics and advanced signal processing technologies is a cost-effective solution to upgrade the transmission capacity. This thesis focuses on the physical links in PONs-methods and signal processing technologies involved in increasing the capacity are discussed. Ultimately, this research may pave the way for the upcoming bandwidth-consuming online technologies that make use of the infrastructure of the modern Internet

5G System Technological Enhancements Provided by Fiber Wireless Deployments

Europeiska kommissionen (EU) (EC/H20207224295), 2017-06-01 -- 2020-05-31.

Europeiska kommissionen (EU) (EC/H20207224295), 2017-06-01 -- 2022-03-31.


Informations- och kommunikationsteknik


Hållbar utveckling

Innovation och entreprenörskap


Elektroteknik och elektronik




Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5044



Room EC, Hörsalsvägen 11, 5th floor, Chalmers University of Technology, Johanneberg campus, and Via Zoom


Opponent: Dora van Veen, Nokia Bell Labs, USA

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