Data-aided Iterative Algorithms for Linearizing IM/DD Optical Transmission Systems

—DSP-enhanced intensity-modulation direct-detection
(IM/DD) systems can support up to 56 Gb/s over 100 km signal
transmissions at C-band. To achieve higher data rates and longer
transmission distances, we propose data-aided iterative algorithm
(DIA) and decision-directed DIA (DD-DIA) to digitally mitigate
signal-signal beating interference (SSBI) without requiring any
modifications to physical layer structures. DIA utilizes pilot
symbols with uniformly spaced insertions to relax the modified
Gerchberg-Saxton (G-S) algorithms that suffer from the local
optimum problem. To further improve the symbol error rate
(SER) performance and convergence speed, DD-DIA introduces a
decision process to generate pseudo-pilots. We numerically
compare DIA with other algorithms and find that DIA can
recover signals subject to large fiber dispersions corresponding to
which conventional IA and Volterra filter (VF) fail, while DD-DIA
significantly accelerates the convergence speed and improves the
reconstruction performance compared with DIA, it can support
100-Gb/s PAM4 over 400-km IM/DD transmissions within just 50
iterations. Two orders of magnitude reductions in SER is
observed for 100 Gb/s PAM4 signal transmission over 100-km
SSMFs. Compared with conventional IA, the proposed techniques
have higher convergence speeds, better global optimum features
and large tolerances to physical model errors. In particular,
DD-DIA results in larger optical signal-to-noise ratio (OSNR)/
received optical power (ROP) improvement, higher transmission
capacities and less computational complexity. DD-DIA is a
promising algorithm for efficiently reconstructing 2-dimensional
optical field for conventional IM/DD optical transmission systems.
Index Terms—Optical communication, digital signal
processing, IM/DD system, field reconstruction.