PAPR reduction with low-complexity pre-conditioned and orthogonal phase shaping in 400G coherent TFDM PON

Coherent time- and frequency-division multiplexing (TFDM) passive optical network (PON) provides flexible resource allocation and low-latency access. However, the peak-to-average power ratio (PAPR) increases with the number of subcarriers, leading to reduced launch power and power budget. In this Letter, we propose and experimentally demonstrate a low-complexity PAPR reduction scheme for 400-Gb/s coherent TFDM PON. The proposed pre-conditioned and orthogonal phase shaping (POPS) scheme first applies Schroeder phase pre-conditioning to suppress subcarrier phase alignment and then selectively performs Walsh-Hadamard-structured phase shaping only for high-PAPR blocks. The block-wise phase rotations are recovered using embedded pilots, avoiding explicit side-information transmission. In a 20-km 400-Gb/s coherent TFDM PON experiment with 4-16 digital subcarriers, POPS achieves up to 6.02-dB PAPR reduction and 5.76-dB power-budget improvement with only 1.76% symbol overhead, while reducing the phase-search complexity to linear order.