Performance Analysis of O-band PAM4 Short-Reach IM/DD Systems for Inter-Datacenter Applications

In recent years, due to the increase in global traffic and the spread of artificial intelligence (AI) applications and large language models (LLMs), the expansion of data centers has accelerated significantly, with annual growth rates reaching approximately 27% since 2017. Like in modern communication networks, also data communications (datacom) are primarily based on optical fiber technologies due to their large bandwidth, low signal attenuation and resistence to electromagnetic interference and environmental factors. Nowadays, the goal in inter-datacenter environments is to achieve high-speed data transmission (1.6 Tb/s and above) over short distances (in the range of 2-10 km). For costs reasons, this type of systems relies on solutions based on intensity modulation, in the form of Pulse Amplitude Modulation (PAM), and direct detection (IM-DD). However, compared to coherent systems, characterized by a higher spectral efficiency, IM-DD systems require higher symbol rates and larger channel spacings to reach such high bit rates. Recent studies have revived the interest in the O-band for inter-datacenter transmissions, due to the lower chromatic dispersion (zero at ~1310 nm) compared to the C-band. This thesis focuses on the performance evaluation of IM-DD systems operating in the O-band with Wavelength Division Multiplexing (WDM) architectures, employing a high symbol rate of 112 GBd and a channel spacing of 400 GHz. Through simulations, the thesis analyzes the degrading factors of this transmission performance, including inter-symbol interference (ISI) and chromatic dispersion (CD), to better understand their impact on the quality of transmitted data and system reliability. By extracting meaningful insights, this work seeks to contribute to the optimization of short-reach optical communication systems designed for the next generation of high-speed data centers.