Mid-Span Spectral Inversion for Coherent Optical OFDM Systems: Fundamental Limits to Performance

Abstract—We develop a theoretical expression to predict the ultimate back-to-back performance of coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems that rely on four-wave mixing to achieve phase conjugation for mid-span spec-tral inversion. Our analysis shows that two different two-stage nonlinear processes produce strong noise-like products in the conjugated signal band. We verify our theoretical results with simulations and experiments; these both show excellent agree-ment with the analytical theory. We identify the optimal design parameters and predict that optical phase conjugation of 10 THz wide orthogonal frequency-division multiplexing signals could be possible, given appropriate dispersion management of the non-linear element. We also experimentally demonstrate the benefit of MSSI in an 800 km transmission of CO-OFDM. Index Terms—Coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems, mid-span spectral inversion (MSSI), optical phase conjugation (OPC), Kerr nonlinearity. I