Techniques for Enabling High-Order Modulation Formats in Short-Reach Optical Communication Networks Based on Directly Modulated Lasers

• Main Author: Deb, Nebras
• Other Authors: Electrical and Computer Engineering, Cartledge, John
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Directly modulated laser; DML; FDM; Fiber optics; Kramers Kronig receiver; Optical communications; Optical networks; Power loading; SCM; Short reach
• Online Access: http://hdl.handle.net/1974/28645

The need to satisfy bandwidth-hungry applications with a growing number of internet users has raised the requirements for capacity and reach in optical communication systems. Recent advances in field modulation and digital coherent detection enabled applications in long- and medium-reach systems. For short-reach systems, such as intra- and inter-data center connections, solutions which consider their sensitivity to both cost and system complexity are required. Systems based on intensity modulation and direct detection (IM/DD) are good candidates to fulfill the requirements of many short-reach applications. In an IM/DD channel, chromatic dispersion and the dispersion-induced frequency-selective power fading are major issues which limit the system performance. The primary objective of this research is to enhance the transmission performance in IM/DD systems, with a focus on using a transmitter based on a directly-modulated laser (DML). The capacity and reach of an IM/DD system are improved by employing higher-order modulation formats and mitigating chromatic dispersion and the resulting frequency-selective power fading. For this purpose, two main approaches are investigated by simulation. In both approaches, higher-order modulation formats are enabled by employing subcarrier modulation (SCM) with a transmitter based on the direct modulation of a 10 Gb/s commercial packaged laser. For modeling the laser, a rate-equations model is adopted. The values of the rate equations parameters and the elements in an equivalent circuit model for the electrical interface are extracted based on a series of measurements using a comprehensive procedure. In the first approach, several radio frequency (RF) channels using the same modulation format are multiplexed before driving the DML. The frequency-selective power fading is mitigated by optimizing the modulation conditions of the DML and employing power loading of the RF channels. Using a practical two-tone test and the received signal-to-noise-and-distortion ratios, an iterative ...