Frequency offset and phase noise-tolerant coherent PON with fast convergence for upstream.

• We experimentally demonstrate a frequency offset and phase noise-tolerant coherent PON with simplified DSP. • We achieve 30.4-dB and 40.0-dB power budget with 100-Gb/s PAM-4 and 50-Gb/s OOK signal using only 20-ns preamble. • We use unequally-spaced PAM-4 to compensates for the modulator nonlinearity and brings 1.9-dB sensitivity improvement. Coherent optics are considered a promising solution for 100G passive optical network (PON) and beyond. Both simplified structure and efficient preamble are desired for the cost-sensitive scenario and upstream burst mode detection. In this work, we experimentally demonstrate a phase-insensitive coherent PON. An optical carrier is added by the modulator bias as an offset in signal constellation to eliminate the phase ambiguity, which can remove the carrier frequency and phase recovery stages. Signal-phase least-mean-square (SP-LMS) equalizer is used to eliminate the inter-symbol interference based on the amplitude-only constraint. By using a 20-ns preamble, 100-Gb/s 4-level pulse amplitude modulation (PAM-4) signal is successfully transmitted over 25-km standard single-mode fiber with 30.4-dB power budget. The frequency offset and phase noise-tolerant scheme is a potential candidate for future cost-effective coherent PON. [ABSTRACT FROM AUTHOR]