Simplified Coherent Photonics-Aided D-Band Fiber-THz Integrated System With Adaptive Kramers–Kronig Scheme and Probabilistic Shaping

Simplified coherent detection technology is a promising solution for saving receiver costs in ultra-high data rate photonic-aided terahertz communication systems. One of the key issues in the simplified system when using envelope detector (ED) is that the generation of signal-to-signal beating interferences (SSBI) reduces the signal-to-noise ratio (SNR). Kramers-Kronig (KK) algorithm could effectively eliminate SSBI. In this study, we demonstrated the feasibility of adaptive KK (AKK) in a simplified coherent photonics-aided terahertz system in the D-band. Nonlinearity and inter symbol interference (ISI) are two major challenges that limit the capacity and rate of terahertz systems. The advantage of adaptive KK lies not only in effectively eliminating nonlinearity in the system, but also in considering the impact of ISI and incorporating equalizers into the AKK scheme. Simulation and experimental results show that AKK has improvement in terms of driving voltage range, received optical power, and carrier signal power ratio (CSPR) compared to traditional KK methods. Furthermore, based on proposed AKK scheme, a line rate of over 80 Gbps and a net rate of over 60 Gbps are realized through 10-km standard single-mode fiber (SSMF) and 0.5-m wireless distance with the probabilistic shaping (PS) technology in the 137-GHz fiber-THz integrated communication system.