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Impact of Analog and Digital Pre-emphasis on the Signal-to-Noise Ratio of Bandwidth-limited Optical Transceivers

Zhou, Z; Odedeyi, T; Kelly, B; O'Carroll, J; Phelan, R; Darwazeh, I; Liu, Z; (2020) Impact of Analog and Digital Pre-emphasis on the Signal-to-Noise Ratio of Bandwidth-limited Optical Transceivers. IEEE Photonics Journal p. 1. 10.1109/jphot.2020.2966617. Green open access

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Abstract

The ever-growing machine-to-machine traffic in data centers has stimulated the increase of transceiver data rate from 25Gb/s/λ to 100Gb/s/λ and beyond. It is believed that advanced modulation formats and digital-to-analog converters (DACs) will be employed in next generation short-reach transceivers. Digital pre-emphasis techniques are widely employed in DAC-based transceivers to compensate for the high frequency roll-off due to the RF and optoelectronics components in optical transceivers. However, digital pre-emphasis essentially reduces the magnitude of the signal low frequency components for a flat frequency response, which unavoidably increases quantization error, reducing the overall signal-to-noise ratio. This trade-off between SNR and bandwidth conflicts with the high SNR requirement of advanced modulation formats such as the Nyquist-shaped pulse amplitude modulation (PAM). To mitigate the quantization error induced SNR degradation, we show that analog pre-emphasis filters can be used in conjunction with digital pre-emphasis for improved system performance. To understand the impact of the analog pre-emphasis filter on system performance, we analyze the relationship between the flatness of the system frequency response and the SNR degradation due to digital pre-emphasis, and demonstrate 1.1-dB increase of receiver sensitivities, for both 64-Gb/s and 128-Gb/s intensity-modulation direct detection (IM-DD) 20 PAM4 signals, respectively employing a directly modulated laser (DML) and an electroabsorption modulator (EAM).

Type: Article
Title: Impact of Analog and Digital Pre-emphasis on the Signal-to-Noise Ratio of Bandwidth-limited Optical Transceivers
Open access status: An open access version is available from UCL Discovery
DOI: 10.1109/jphot.2020.2966617
Publisher version: https://doi.org/10.1109/JPHOT.2020.2966617
Language: English
Additional information: This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/.
Keywords: Optical transmitter , Data center interconnection , Directly-modulated laser (DML) , Externally-modulated laser (EML) , Digital signal processing (DSP) , Pulse amplitude modulation (PAM) , Digital pre-emphasis , RF equalization
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10091142
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