Clock Recovery Challenges in DSP-Based Coherent Single-Mode and Multi-Mode Optical Systems

Abstract

We present an analysis of clock recovery algorithms in both polarization division multiplexing systems and mode division multiplexing systems. The impact of inter-polarization time skew and polarization mode dispersion in single-mode fibers, as well as the combined impact of mode mixing and mode group delay spread in multi-mode fibers under different coupling regimes are investigated. Results show that although the clock tone vanishing has a known solution for single-mode systems, in multi-mode systems even for low group delay spread, strong coupling will cause clock tone extinction, making it harder to implement an effective clock recovery scheme.

Adaptive Coherent Receiver Settings for Optimum Channel Spacing in Gridless Optical Networks

“…In [8], the authors introduced a new circuit to digitally adjust the SOP of the dual-polarization signal, used to extract clock tone, to avoid losing lock and to improve timing recovery. In [9,10], the authors studied the impact that coupling has on synchronization in multi-mode coherent optical systems. They showed how for even a small group delay (0.1 ps/km) will weaken the strength of the clock tone.…”