Digital pre-equalization for performance improvement in coherent PON

As high-speed optical access networks continue to evolve, reducing the computational complexity at the optical network unit (ONU) side remains a significant challenge in coherent passive optical network (PON). This paper presents a pre-equalization scheme that integrates digital pre-distortion (DPD) and pre-emphasis techniques in 200 Gb/s coherent PON. The focus is on three modulation formats: 50 Gbaud polarization multiplexing-quadrature phase shift keying (PM-QPSK), 50 Gbaud Alamouti-coded polarization multiplexing-16 quadrature amplitude modulation (PM-16QAM), and 25 Gbaud PM-16QAM, using intradyne or heterodyne detection schemes. Through comprehensive numerical simulations and experimental evaluations, we demonstrate significant improvements in receiver sensitivity and power budget in 200 Gb/s coherent PON. When the number of digital filtering taps is small, the proposed scheme achieves power budget enhancements of 3 dB for 50 Gbaud PM-QPSK, 7 dB for 50 Gbaud Alamouti-coded PM-16QAM, and 2.1 dB for 25 Gbaud PM-16QAM in the downlink. These findings highlight the potential of pre-equalization techniques in enhancing the performance of next-generation coherent PON with low computational complexity at the ONU side.