Abstract
In this paper, we propose a nonlinear Tomlinson-Harashima pre-coding (THP) scheme for nonlinear distortion suppression in direct-detected double sideband (DSB) PAM-4 transmission systems. Based on the traditional THP, the feedback term is modified by introducing nonlinear components. In this way, more accurate feedback can be obtained to mitigate the signal distortions, especially the nonlinear distortions including the signal-to-signal beating interference and nonlinear power series caused by chromatic dispersion and square-law detection. Meanwhile, we also propose to only reserve the nonlinear kernels with adjacent tap products in nonlinear THP, for the purpose of computation complexity reduction. To verify the effectiveness, transmissions of double sideband (DSB) PAM-4 signal in 1550nm window are experimentally demonstrated. Volterra FFE is adopted on the receiver side to suppress linear and nonlinear pre-cursors. We optimize various parameters of hardware and apply appropriate simplification to the nonlinear THP kernels. The results indicate that, the proposed nonlinear THP can lead to up to three folds BER reduction, compared to the conventional linear THP. Finally, with the combination of proposed nonlinear THP and conventional Volterra FFE, we successfully transmit 84-Gbps PAM-4 and 107-Gbps PAM-4 respectively over 80 km and 40 km under the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10-3.
Highlights
With the emergence of diverse new scenarios, including mobile fronthaul, high-speed optical access, data center interconnects and so forth, advanced optical short-reach transmission systems with both upgraded capacity and extended reach are urgently needed, to bear the continuous traffic growth [1]
In this paper, we propose a nonlinear Tomlinson-Harashima pre-coding (THP) scheme for nonlinear distortion suppression in direct-detected double sideband (DSB) pulse amplitude modulation (PAM)-4 transmission systems
Two transmission cases are tested, including 84-Gbps over 80 km and 107-Gbps PAM-4 signal over 40 km
Summary
With the emergence of diverse new scenarios, including mobile fronthaul, high-speed optical access, data center interconnects and so forth, advanced optical short-reach transmission systems with both upgraded capacity and extended reach are urgently needed, to bear the continuous traffic growth [1]. One straightforward way is compensating the chromatic dispersion (CD) with a dispersion compensation module (DCM), which needs additional optical devices and incurs high insertion loss [5,6] Another promising method is the single sideband (SSB) based transmission with digital signal processing schemes, such as Kramers-Kronig (KK) algorithm or iterative subtraction, for signal-to-signal beating interference (SSBI) cancellation [7,8,9,10]. Using such a method, the generation of SSB signal lies on additional optical filtering or complex in-phase and quadrature (IQ) modulation. Electrical CD pre-compensation can be employed at the transmitter side for DSB signal [11,12], which relies on the IQ modulation with two DACs
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