Equalization techniques for short-reach optical fiber communication systems

Abstract

As the key enablers of optical fiber communication systems, the technologies of intensity modulation and direct detection (IM/DD) and in-phase and quadrature modulation and coherent detection (IQM/CohD) have been studied extensively in the past 40 years. Nowadays, CohD based systems have enabled transmission of up to 100 Tb/s over thousands of kilometers, using advanced signal processing techniques to mitigate various transmission impairments. However, for many applications such as inter-data center interconnections (DCIs), CohD is often too complex to be used. IM/DD is preferred due to its simplicity and low power consumption, but its performance is often limited by chromatic dispersion (CD) and limited component bandwidth. In order to meet the requirement of inter-DCIs, various solutions have been proposed. These include equalization algorithms in IM/DD systems at the transmitter and receiver, simplifying the structure and digital signal processing (DSP) in IQM/CohD systems, or realization of mode-division multiplexing (MDM) systems. However, significant research effort is still necessary to reach up to 100-km transmission at high data rate. In view of the above, this thesis focuses on two aspects of powerful equalization algorithms in IM/DD systems with up to 100-km standard single-mode fiber (SSMF) transmissions, and non-singular multi-user constant modulus algorithm (MU-CMA) equalization in mode-division multiplexing (MDM) system. The proposed schemes have been successfully realized experimentally and their dynamic performance has also been evaluated. The IM/DD schemes include iterative and non-iterative pre-electronic dispersion compensations (EDCs) based on the Gerchberg-Saxton algorithm (GSA) and small-signal analysis (SSA), low-complexity post-equalizers with weight sharing (WS), and the joint scheme of combined pulse shaping, nonlinear pre-distortion, and low-complexity post-equalizers. While the MDM scheme applies the proposed 4 x 4 multi-user constant modulus algorithm (MU-CMA) and Kramers–Kronig reception (KKR) to achieve the non-singular MDM transmission with four cylindrical vector (CV) modes and each mode carrying the high-order modulation format of 16-QAM. Overall, the works presented in the thesis shall provide potential solutions to realize short-reach optical fiber communication systems with high speed and good performance.