SOA Enabled Self-Homodyne Coherent Bidirectional Transmission for Metro-Datacenter Interconnects

Self-homodyne coherent bidirectional (SHC-BiDi) scheme has gained much attention as a promising coherent-lite solution for datacenter interconnects (DCIs) recently. However, the twofold propagation loss of parallelly delivered signal and remote local oscillator (LO), as well as the power split loss of laser, severely restrict its power budget, making it inapplicable for metro-DCI networks until now. In this work, we propose a reach-extended, cost-efficient SHC-BiDi scheme suitable for metro-DCI applications. Thereinto, two bidirectionally operated semiconductor optical amplifiers (SOAs), with the signal gain clamped by counter-propagating remote LO, are utilized to simultaneously achieve linear signal amplification and remote LO regeneration. We comprehensively investigate the bidirectionally operated gain-clamped SOA and reach-extended transmission. The results show that the SOA can be transformed into a linear booster signal amplifier by clamping LO at proper power, while long-wavelength clamping reduces the nonlinear distortions of signal more efficiently. Besides, despite the potential cross-phase modulation (XPM) impairments on regenerated LOs, its induced Q
²
factor penalty can be kept below 0.570 dB, when the signal power and LO power injected into the SOA are below −10 dBm and above 0 dBm, respectively. Furthermore, by utilizing the built-in dithers of lasers to suppress the stimulated Brillion scattering (SBS) in LO propagation, successful 400 G dual-polarization 16QAM transmissions are demonstrated over 50 km and 75 km links, with the corresponding transmitter laser power of 13.7 dBm and 18.5 dBm. Wherein, the digital signal processing (DSP) employing simple maximum likelihood (ML) phase recovery is also validated to be feasible under ∼1 MHz laser linewidth.