Hybrid Lumped Repeater Using PPLN-Based High-Gain Optical Parametric Phase Conjugators and EDFAs for C+L-Band Transmission

We propose a C+L-band lumped repeater configuration using optical phase conjugators (OPCs) and erbium-doped fiber amplifiers (EDFAs). The OPC based on a highly efficient and wideband periodically poled LiNbO
₃
(PPLN) waveguide provides a high conversion gain over 15 dB with a flat noise figure. The high-gain OPC functions as a pre-amplifier in the repeater while conjugating and spectrally inverting signal light to mitigate fiber nonlinearity and an effect of stimulated Raman scattering. The post-EDFAs enable the output of high power with little excess signal distortion due to gain saturation of the OPC. We applied the proposed repeater to a 100-GHz-spaced 84-channel C+L-band transmission. A 1120-km standard single-mode fiber transmission with small SNR deviation within 1 dB was achieved using 96-Gbaud PCS-36QAM channels (640 Gbps/ch.) thanks to a uniform noise performance and a spectral inversion effect of the OPC. We also applied it to a non-zero dispersion fiber link. The proposed repeater could made available the low-dispersion band in the C-band, and the six represented channels over the C+L-band were transmitted over 480 km with 640 Gbps.