Evolution of digital coherent optical transmission technology

Abstract

Transmission data capacity and its achievable distance were expanded by the invention of digital coherent detection technology utilizing digital signal processing, since digital coherent detection enables polarization multiplexing, quadrature amplitude modulation, and signal distortion equalization. This paper describes the basic principles of the key technical elements such as coherent detection and digital carrier phase lock, chromatic dispersion of optical fiber and its equalization, and adaptive equalization filters for polarization demultiplexing and signal distortion equalization. We give an overview of the general structure of optical transceivers for a digital coherent transmission system including data coding, digital signal processing, and analog components and, we introduce some recent novel techniques.