Advanced nonlinearity equalizer with TC-NL-MLSE for transmitting beyond 200-Gb/s PAM-8 in IM/DD systems

Abstract

The severe band-limited effect resulted from the low-cost optical transceiver increases the channel memory length and the number of taps of the equalizers. Besides, the interaction of fiber dispersion and square-law detection introduce nonlinear distortions in intensity modulation and direct-detection (IM/DD) transmission systems. The serious band-limited effect and nonlinear distortions degrade the transmission performance and bring challenges to current equalizers for low-complexity implementation. In this paper, we propose a trellis-compression nonlinear maximum likelihood sequence estimation (TC-NL-MLSE) algorithm to compensate the linear and nonlinear distortions with lower complexity. In the TC-NL-MLSE, we introduce a polynomial nonlinear filter (PNLF) to partly compensate both the linear distortions and nonlinear distortions. Then, we establish a look-up-table (LUT) to calculate the nonlinear branch metric (BM). To simplify the calculation, two or three levels with the highest probabilities are selected according to decision thresholds for each symbol to compress the state-trellis graph (STG). This significantly reduces computational complexity on BM calculations especially for high-order modulations. We conduct experiments to transmit beyond the 200-Gb/s PAM-8 signal over 2-km standard single mode fiber (SSMF) at C-band. The TC-NL-MLSE outperforms the reduced-state MLSE with PNLF, and can reach the 7%-overhead hard-decision forward error correction threshold. Moreover, the TC-NL-MLSE reduces the complexity by 97% compared with standard LUT-MLSE, limiting the multipliers around 100 at the expense of only 0.2-dB receiver sensitivity penalty.

Semiconductor Optical Amplifier (SOA)-Driven Reservoir Computing for Dense Wavelength-Division Multiplexing (DWDM) Signal Compensation

“…[1][2][3]. However, the advanced modulation format, e.g., high-order quadrature-amplitude modulation (QAM), requires a higher optical signal-to-noise ratio (OSNR), resulting in optical signal processing (OSP) as the crucial function at the optical receiver [4][5][6]. A digital signal processing (DSP)based OSP could perform the functions of frequency and phase estimation, dispersion compensation, channel equalization, etc., enabling mitigation of impacts from the linear or nonlinear effects in the transmission link.…”

Look-Up-Table-Based Direct-Detection-Faster-Than-Nyquist-Algorithm-Enabled IM/DD Transmission with Severe Bandwidth Limitation

“…LUT is an efficient scheme to mitigate the pattern-dependent distortion. Meanwhile, trellis-compression MLSE (TC-MLSE) equalizer has been proposed and used in IM/DD transmission systems [24,25]. Inspired by the effectiveness of LUT, we propose the LUT-based DDFTN algorithm.…”

Integer codes correcting single errors and double adjacent errors

“…The essence of our idea is to replace the IC with integer single-error-correcting-double-adjacent-error-correcting (SEC-DAEC) codes. The use of such codes could significantly improve data transmission between edge routers and end nodes (computers and servers), especially if they are interconnected by optical links (according to [9][10][11][12][13][14][15][16], 87% to 99% of all channel errors, which occur on optical links, are single and double adjacent (DA) errors). In addition, the receiver would not be subject to any hardware changes, since the proposed codes are a generalization of the IC.…”