Clipping PAM4 for 56G ER Optical Interconnects Using Cost-Effective 10G-Class TOSA and ROSA

Amplifier-free O-band intensity modulation direct detection (IM/DD) optical system has been applied in the extended-reach (ER) optical interconnects. The amplifier-free IM/DD optical systems are peak-power constrained, in which a high-peak-to-average power ratio (PAPR) signal leads to a low optical power budget. In this paper, we propose the symmetric clipping operation to reduce the high PAPR of the Nyquist-shaping four-level pulse amplitude modulation (PAM4) signal, and the clipping noise cancellation (CNC) to remove the clipping noise. 56G PAM4-based ER optical interconnects are experimentally demonstrated by using 10G-class transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA). The experimental results show that the clipping operation and CNC algorithm can bring down the bit error ratio under the KP4 forward-error-correction limit of $2.2\times 10^{-4}$ at the received optical power of −16dBm. Based on the proposed algorithm, the optical power budget of 56G PAM4-based ER optical interconnects is ∼ 24dB, which is ∼ 3dB higher than that using only clipping operation. The sufficient optical power budget makes the cost-effective 10G-class optical components feasible for ER optical interconnects.