Abstract
Eigenvalue-based communication technologies using inverse scattering transform (IST) have gained attention as a new transmission strategy in optical fiber communications. In recent years, several studies on artificial neural network (ANN)-based equalization and demodulation schemes for eigenvalue-modulated signal have been conducted to enhance the receiver sensitivity. However, in the case of a presence of a carrier frequency offset (CFO) at receiver, the effects of the CFO on ANN receiver of eigenvalue-modulated signal is yet to be reported. In this study, we numerically and experimentally investigated the generalization performances of eigenvalue domain ANN-based demodulator on CFO. Furthermore, we propose to combine an ANN-based demodulator with a CFO compensation method based on IST and a relation between frequency and eigenvalue shifts. The proposed method, based on an appropriate soliton pulse, achieves a high CFO estimation accuracy of submegahertz order even if the CFO reaches <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 2.5 GHz under the noiseless condition. In the presence of noise and a large CFO of 2.5 GHz, the method attains a CFO estimation accuracy below 60 MHz for OSNR = 10 dB with a low pilot pulse rate, such as 0.064%. We show the simulation results obtained after applying the proposed CFO compensation to the ANN demodulator, which is valid for 2.5 GHz CFO and long-haul transmission over 5000 km. Experiments performed in this study demonstrate successful demodulation of an eigenvalue-modulated signal with OSNR penalty <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$< $</tex-math></inline-formula> 1 dB in the presence of CFO within 1 GHz at 2.5 Gb/s.
Highlights
O PTICAL eigenvalue communication [1] based on inverse scattering transform (IST) [2] has been recently gained attention because it is unaffected by the Kerr nonlinearity in optical fibers [3]–[24]
It was found that the conventional eigenvalue domain (ED)-artificial neural network (ANN) demodulator cannot cover an eigenvalue-modulated signal with a large carrier frequency offset (CFO) over 1 GHz
To enhance the generalization performance of the ED-ANN on CFO, we proposed to combine an ED-ANN with an IST-based CFO compensation method
Summary
O PTICAL eigenvalue communication [1] based on inverse scattering transform (IST) [2] has been recently gained attention because it is unaffected by the Kerr nonlinearity in optical fibers [3]–[24]. A bidirectional long short-term memory gated recurrent neural network equalizer has been proposed and shown to outperform a feed-forward ANN equalizer at a spectral amplitude of 64-QAM of spectral amplitude [19] These ANN-based receivers have been demonstrated only with a small static CFO ≤ 100 MHz generated by simulation or using acousto-optic modulator in experiment. For on–off encoding of multieigenvalue, the authors have proposed an eigenvalue domain (ED)-ANN-based demodulation method, which does not require model training for each transmission distance [15]. Experiments performed in this study demonstrate successful demodulation of an eigenvalue-modulated signal with OSNR penalty < 1 dB in the presence of CFO within 1 GHz at 2.5 Gb/s.
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