Abstract
In this paper, a machine learning-based tunable optical-digital signal processor is demonstrated for a short-reach optical communication system. The effect of fiber chromatic dispersion after square-law detection is mitigated using a hybrid structure, which shares the complexity between the optical and the digital domain. The optical part mitigates the chromatic dispersion by slicing the signal into small sub-bands and delaying them accordingly, before regrouping the signal again. The optimal delay is calculated in each scenario to minimize the bit error rate. The digital part is a nonlinear equalizer based on a neural network. The results are analyzed in terms of signal-to-noise penalty at the KP4 forward error correction threshold. The penalty is calculated with respect to a back-to-back transmission without equalization. Considering 32 GBd transmission and 0 dB penalty, the proposed hybrid solution shows chromatic dispersion mitigation up to 200 ps/nm (12 km of equivalent standard single-mode fiber length) for stage 1 of the hybrid module and roughly double for the second stage. A simplified version of the optical module is demonstrated with an approximated 1.5 dB penalty compared to the complete two-stage hybrid module. Chromatic dispersion tolerance for a fixed optical structure and a simpler configuration of the nonlinear equalizer is also investigated.
Highlights
The well-known increase in information rate is a particular concern for inter-data center communication due to chromatic dispersion (CD)
Using only electronic processing with an Neural Network (NN) equalizer or maximum likelihood sequence estimation (MLSE), we showed a transmission of 164 ps/nm of accumulated CD (10 km of equivalent standard single-mode fiber (SSMF)), considering a 0 dB SNR penalty at KP4 FEC compared to a back-to-back transmission
We showed a tuneable hybrid signal processing system to increase the maximum transmission reach for a direct detection (DD) system
Summary
The well-known increase in information rate is a particular concern for inter-data center communication due to chromatic dispersion (CD). Optical dispersion compensation modules as fiber Bragg grating and dispersion compensation fibers are more commonly used to compensate for the CD in the optical domain They are not easy to tune and need to be designed for a specific link. We show that the performance can be improved using the optical component with fewer sub-bands if a further stage of equalization in the digital domain is applied. A complexity reduction is demonstrated by using half of the proposed optical module structure together with an NN equalizer This approach slightly reduces the gain, but can be attractive for inter-data center communication due to the reduced footprint. The former is the optical structure used to mitigate CD, and the latter describes the NN equalization and training process.
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