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Towards 50 Gb/s in High-Speed PON: Optimization of Modulation Formats Using Pre-Chirping

High-Speed (HS) Passive Optical Network (PON) alternatives with single-wavelength capacity higher than 10 Gb/s, such as 25 and 50 Gb/s, are currently under investigation, development and standardization. Modulation formats based on intensity modulation and direct detection (IM-DD) have been preferred to implement next generation HS-PON due to their advantages in terms of complexity and cost. Among them, conventional Binary Pulse Amplitude Modulation (PAM-2) format, as well as Quaternary PAM (PAM-4) and Electrical Duo-Binary (EDB), have been emerged as the most widely employed. In previous works, we have shown that any of these formats is feasible for the transmission of 50 Gb/s using currently available 25 Gb/s technology when operating in C-band of single mode fibre (SMF) for typical PON distances (i.e., 20 km). In this contribution, we introduce the use of pre-chirping technique in order to overcome this reach limitation. We compare the achievable performance of PAM-2, PAM-4 and EDB under demanding bandlimited and dispersive conditions on the transmission of 50 Gb/s using adaptive equalization, with and without pre-chirping. By means of simulations, we demonstrate that using pre-chirping enables the operation of PAM-2 and PAM-4 on the transmission of 50 Gb/s through 20-km of SMF in O- and C-band, respectively, using currently available technology.