Abstract

Look-up table (LUT) is an efficient digital pre-distortion (DPD) technique at the transmitter side (Tx) to mitigate the pattern-dependent impairment arising in the intensity-modulation direct-detection (IM-DD) transmission. When the long-memory nonlinear inter-symbol interference (ISI) occurs for the high-speed IM-DD transmission, both the peak-to-average power ratio (PAPR) of the pre-distorted signal and the implementation complexity of LUT increases fiercely along with the growing memory length of LUT. Here, relying on the error distribution of the received symbol with respect to amplitudes of previous symbols and next symbols, we propose a low-complexity multi-symbol simplified LUT (MSS-LUT)-based DPD, by pruning the LUT entries via the pre-fixed threshold. Meanwhile, we jointly optimize the modulation depth and the clipping ratio to maximize the performance of the proposed MSS-LUT-based DPD scheme. The effectiveness of the proposed MSS-LUT-based DPD scheme is experimentally verified, under the condition of C-band four-level pulse amplitude modulation format (PAM-4) back-to-back (B2B) transmission with variable baud rates and memory lengths. When 100 GBaud/λ PAM-4 is transmitted, the size of MSS-LUT is reduced by 91.4%. This value is in comparison with the case of a full-size LUT with a memory length of 5 (LUT-5), together with only a 0.3 dB penalty of received optical power (ROP).