Hardware-Efficient and Performance-Enhanced Joint Pulse Shaping and Dispersion Compensation for Coherent Data Center Interconnects

摘要

With the explosion of data traffic triggered by 5G/6G and Generative artificial intelligence, coherent optical communication is moving towards higher baud rates and more complex modulation formats. This leads to a significant increase in the computational complexity and power consumption of digital signal processing (DSP) at the transmitter and receiver ends, especially in the chromatic dispersion(CD) Compensation and low roll-off shaping filter modules. We propose a joint shaping filtering and CD compensation (JFS-CD) algorithm. This algorithm moves the CD compensation to the transmitter side and utilizes the characteristics of discrete fourier transform and the spectral features of shaping filtering for integrated processing. Aiming at the high peak-to-average power ratio (PAPR) problem caused by chromatic dispersion pre-compensation, we propose a low-complexity square boundary clipping algorithm(SBC). Simulation results show that, under the premise of maintaining unchanged performance, JFS-CD can reduce the real multiplication complexity by about 46%. Meanwhile, benefiting from the suppression of the effects of system nonlinearity and receiver IQ imbalance, the joint JFS-CD and SBC scheme improves the Q-factor by about 0.3 dB in experiments compared to the traditional post-chromatic dispersion compensation scheme. This research provides a highly potential transmitter DSP solution for next-generation low-power and high-performance data center interconnects (DCI).

核心问题与主要方法

核心问题

Reduce DSP complexity and power consumption for pulse shaping and chromatic dispersion compensation in coherent optical data center interconnects

场景：Transmitter-side DSP for high-baud-rate coherent optical links, using blockwise FFT/IFFT processing and pre-compensation in coherent DCI

主要方法

JFS-CD moves CD compensation to the transmitter and combines it with pulse shaping by multiplying their frequency-domain transfer functions into a joint operator. The implementation uses blockwise N-point FFT, DFT scale/transformation behavior to form a 2N oversampled frequency-domain representation, pointwise multiplication by the joint response, and 2N-point IFFT back to time domain. Complexity reduction comes from the spectral support of the shaping filter: coefficients outside the roll-off bandwidth are zero, and the resulting sparse/zero regions reduce required multiplications and IFFT work. SBC limits CD pre-compensation peaks using threshold comparisons on real and imaginary components, avoiding square-root-heavy magnitude clipping and claiming negligible extra multiplication cost. A stationary-phase or phase-consistency argument is used to explain why CD pre-compensation can create high waveform peaks for certain data-dependent quadratic phase patterns.

关键贡献与后续阅读

关键贡献

Introduces JFS-CD, a transmitter-side joint frequency-domain operation that performs pulse shaping and chromatic-dispersion pre-compensation together instead of as separate cascaded DSP modules. Uses the shaping filter spectral support and DFT-based block processing to reduce real multiplication complexity, with the payload reporting about 46% reduction at N=128 and ROF=0.01 versus a cascaded shaping plus CD compensation baseline. Adds square boundary clipping as a low-complexity PAPR-control step for CD pre-compensated waveforms, using real/imaginary threshold comparisons rather than full complex-magnitude clipping. Provides both simulation and experimental evidence in a coherent optical DCI-like setup, including no apparent JFS-CD Q-factor penalty across several ROFs in simulation and about 0.3 dB experimental Q-factor improvement for JFS-CD plus SBC over post-CD compensation. Connects the observed experimental improvement to two mechanisms stated in the payload: reduced nonlinear impact from lower effective PAPR and reduced interaction between receiver IQ imbalance and CD when compensation is moved to the transmitter.

研究启发

How does JFS-CD compare against prior integrated frequency-domain filtering or chirp-filtering approaches under identical implementation assumptions? Are memory movement, FFT scheduling, overlap/discard overhead, and fixed-point quantization included in the hardware-efficiency estimate, or only real multiplication counts? How stable are the Q-factor and PAPR benefits across longer links, other modulation formats, higher baud rates, and different clipping-ratio selection rules? Does SBC introduce measurable out-of-band emissions, EVM penalties, or nonlinear distortion under practical transmitter bandwidth and DAC constraints?

限制与不确定性

Novelty may be incremental if joint FFT-domain filtering/pre-compensation resembles prior optical DSP integration work. Reported benefits may be sensitive to evaluated baud rate, modulation, block sizes, clipping ratio, OSNR, and 100 km SSMF setup. Structure analysis is strong but still second-order evidence; full review is needed to verify comparisons and experimental rigor.

参考文献

3 条

[1] G. Gomes, P. Freire, J. E. Prilepsky, and S. K. Turitsyn, “Fpga implementation of low-power multiplierless pre-processing free chromatic dispersion equalizer,” in 2025 Optical Fiber Communications Conference and Exhibition (OFC) , 2025, pp. 1–3.
[2] A. Felipe and A. L. N. d. Souza, “Chirp-filtering for low-complexity chromatic dispersion compensation,” Journal of Lightwave Technology , vol. 38, no. 11, pp. 2954–2960, 2020.
[3] E. P. da Silva and D. Zibar, “Widely linear equalization for iq imbalance and skew compensation in optical coherent receivers,” Journal of Lightwave Technology , vol. 34, no. 15, pp. 3577–3586, 2016.