Coherent detection associated with digital signal processing for fiber optics communication

Optical transmission systems have seen their performance (system capacity and system reach) drastically improved in the last 15 years by using new technologies such as wide band optical amplification, wavelength division multiplexing (WDM), dispersion management, introduction of 10 Gbit/s channel rate and now 40 Gbit/s, Differential Phase Shift Keying (DPSK) modulation… . In order to further increase system capacity while relaxing the constraints associated with higher channel rate (i.e. 100 Gbit/s), the association of multilevel modulation format with coherent detection and digital signal processing appears as a key enabler. This article describes the actual modulation and detection methods in order to explain how a coherent receiver including digital signal processing works. The efficiency of coherent receiver to compensate for linear distortions induced by fiber optic propagation will also be detailed. The promising association of coherent receiver with multilevel modulation format, especially for 100 Gbit/s channel rate will be described. Eventually, the limitations of optical communication systems relying on coherent detection will be explained. To cite this article: G. Charlet, C. R. Physique 9 (2008).