Abstract

In intensity-modulation and direct-detection (IM-DD) communication systems, electrical chromatic dispersion (CD) compensation cannot be directly applied in the transceivers due to the absence of phase information. Gerchberg-Saxton (GS) algorithm has been utilized to iteratively solve for real-valued CD pre-compensated signal in an IM-DD system. In this scheme, the amplitude information at the transmitter and phase information before the direct detection receiver are treated as the degree of freedoms (DoFs) and jointly optimized. In this paper, a modified GS algorithm is proposed and experimentally demonstrated for CD pre-compensation in a 28-GBaud PAM-4 system over 80-km single mode fiber (SMF) transmission. Compared with the basic GS electrical dispersion pre-compensation (pre-EDC) scheme, the amplitude information of received samples at the T/2 position is regarded as DoFs as well, in order to reduce the error. Besides, to accelerate the convergence speed, two error reversing factors associated with the phase error at the transmitter and amplitude error at the receiver are introduced. The experimental results show that the bit error rate (BERs) of 56-Gbps PAM-4 signal over 80-km SMF transmission without CD compensation and with 10 iterations of basic GS pre-EDC scheme are 2.35×10⁻¹ and 5.13×10⁻², respectively, when a 21-taps feedforward equalizer (FFE) is equipped at the receiver side. While the BER can be reduced to below the hard-decision forward error correction (HD-FEC) threshold of 3.8×10⁻³ by the proposed scheme with the iterative number of 10. The results reveal that the proposed scheme is a promising solution for 50-Gbps class 80-km metro optical communication links based on the IM-DD structure.

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