Innovative solutions for coherent transmission in optical access networks

The increasing demand for capacity in Passive Optical Networks (PONs) is driving operators and vendors to explore new solutions, including the adoption of unamplified coherent technologies. In this study, we investigate a novel approach to enhance transmitted power in coherent PON systems. Our focus is on the Mach-Zehnder Modulator (MZM) and the process of electrical-to-optical signal conversion, introducing a parameter called the modulation index. We explore how the system can operate closer to the nonlinear region of the MZM’s transfer function while maintaining performance. Key performance metrics, including Bit Error Rate (BER) and Optical Distribution Network (ODN) loss, are used to evaluate the system’s behavior. Additionally, we examine the effects of filtering and bandwidth limitations, utilizing a technique called pre-emphasis to compensate for these impacts. Our findings suggest that by reconsidering MZM modulation and accounting for the nonlinear characteristics of the transfer function, it is possible to increase transmitted power for coherent PONs. Given that amplification is not typically used in PONs, this approach could be a viable solution for next-generation coherent PON systems.