Partial Response Advanced Modulation Formats for Bandwidth Limited Optical Links

Research output: Book/ReportPh.D. thesis – Annual report year: 2019Research

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The ever increasing Internet traffic, poses a need for more Bandwidth (BW) of the optical network systems. The required specifications of the optical systems, needed to carry the expected increment in traffic, does not comply with the well known Non-Return to Zero (NRZ) modulation format. Therefore, other modulation formats are considered, among these are Pulse Amplitude Modulation (PAM) and partial response modulation. The most considered modulation format for future Intensity Modulated/Direct Detection (IM/DD) optical systems, is the sub-modulation format, PAM4. As a contester to this modulation format, duobinary modulation is proposed. Duobinary is the lowest level of sub-modulation formats from the partial response modulation format family. The focus on partial response stems from the rapid development of Digital Signal Processing (DSP). Normally DSP is used in long haul applications, but the gained advantages slowly outweighs the increased cost. Partial response has become a viable solution because DSP is moving into short reach IM/DD systems. This thesis analyses the implementation of duobinary and PAM4 in various optical systems, with a focus on solving the band limitations that resides within the systems. Where it is possible, PAM4 and duobinary are compared to each other, and to NRZ, based on Bit Error Ratio (BER) performance. The comparison of NRZ, duobinary and PAM4 is done through theoretical calculations, and followed by experimental validations in the setups presented in the work. The targeted optical systems include; point-to-point connections, data center interconnections and Passive Optical Network (PON) connections. These optical connections are the expected bottlenecks of the Internet. These optical connections are based on IM/DD technology where NRZ is typically used. The state of the art within Dense Wavelength Division Multiplexing (DWDM) PONs includes port agnostics. The inclusion of a Pilot Tone (PT) to control tunable laser sources in new DWDM PONs, means an extension of the theoretical base to include PT modulation. The results presented in this thesis, shows that duobinary is, in most cases, a better suited candidate for modulation format than PAM4.
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages100
Publication statusPublished - 2019

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