Comparison of advanced DSP techniques for spectrally efficient Nyquist-WDM signal generation using digital FIR filters at transmitters based on higher-order modulation formats

Yi Weng; Junyi Wang; Zhongqi Pan

doi:10.1117/12.2206098

13 February 2016 Comparison of advanced DSP techniques for spectrally efficient Nyquist-WDM signal generation using digital FIR filters at transmitters based on higher-order modulation formats

Yi Weng, Junyi Wang, Zhongqi Pan

Author Affiliations +

Proceedings Volume 9773, Optical Metro Networks and Short-Haul Systems VIII; 977305 (2016) https://doi.org/10.1117/12.2206098
Event: SPIE OPTO, 2016, San Francisco, California, United States

Abstract

To support the ever-increasing demand for high-speed optical communications, Nyquist spectral shaping serves as a promising technique to improve spectral efficiency (SE) by generating near-rectangular spectra with negligible crosstalk and inter-symbol interference in wavelength-division-multiplexed (WDM) systems. Compared with specially-designed optical methods, DSP-based electrical filters are more flexible as they can generate different filter shapes and modulation formats. However, such transmitter-side pre-filtering approach is sensitive to the limited taps of finite-impulse-response (FIR) filter, for the complexity of the required DSP and digital-to-analog converter (DAC) is limited by the cost and power consumption of optical transponder. In this paper, we investigate the performance and complexity of transmitter-side FIR-based DSP with polarization-division-multiplexing (PDM) high-order quadrature-amplitude-modulation (QAM) formats. Our results show that Nyquist 64-QAM, 16-QAM and QPSK WDM signals can be sufficiently generated by digital FIR filters with 57, 37, and 17 taps respectively. Then we explore the effects of the required spectral pre-emphasis, bandwidth and resolution on the performance of Nyquist-WDM systems. To obtain negligible OSNR penalty with a roll-off factor of 0.1, two-channel-interleaved DAC requires a Gaussian electrical filter with the bandwidth of 0.4–0.6 times of the symbol rate for PDM-64QAM, 0.35–0.65 times for PDM-16QAM, and 0.3–0.8 times for PDM-QPSK, with required DAC resolutions as 8, 7, 6 bits correspondingly. As a tradeoff, PDM-64QAM can be a promising candidate for SE improvement in next-generation optical metro networks.

Citation Download Citation

Yi Weng, Junyi Wang, and Zhongqi Pan "Comparison of advanced DSP techniques for spectrally efficient Nyquist-WDM signal generation using digital FIR filters at transmitters based on higher-order modulation formats", Proc. SPIE 9773, Optical Metro Networks and Short-Haul Systems VIII, 977305 (13 February 2016); https://doi.org/10.1117/12.2206098

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