Carrier Recovery in Coherent Optical Communication Systems

Carrier recovery is an important building block for modern coherent optical communication systems. This chapter first introduces the concept of carrier recovery and the challenges faced. Before diving into the detail of hardware‐efficient carrier recovery algorithms, the chapter gives a brief introduction to the Cramer‐Rao lower bound (CRLB), CRLB provides us with a more fundamental way to evaluate the effectiveness of various carrier recovery algorithms. Before proceeding to discuss various frequency offset estimation schemes, the chapter focuses on several hardware‐efficient phase estimation algorithms by assuming that the frequency offset has been largely compensated‐for before phase recovery. It describes in more detail three hardware‐efficient multistage phase recovery algorithms that have been demonstrated for high‐SE 100Gb/s and beyond transmission experiments. These are the multistage hybrid blind phase search (BPS)/maximum likelihood (ML) phase recovery algorithm, the hybrid phase‐locked loop (PLL)/ML algorithm, and the training‐assisted two‐stage BPS/ML algorithm.