On Performance Limits for Spectrally Efficient Optical Transmission Techniques in Short-Haul Metro/Access Links

The demand for transmitting optical signals with high spectral efficiency (SE) by exploiting cost-effective systems and techniques is raising an increasing interest in the area of wide or metro area networks (WAN/MAN). Recently, many different solutions, e.g., amplitude modulation formats, direct-detection schemes, line coding, and simple signal processing techniques have been investigated for wavelength division multiplexing (WDM) short haul optical links, where coherent systems turn out to be economically unfavourable. In this article the Time-Frequency Packing technique, already successfully proposed for long-haul coherent optical links, is extended to direct-detection systems, based on pulse amplitude modulation (PAM) and differential phase-shift keying (DPSK), with the purpose of trading between detection complexity and SE, and of providing performance limits for advanced digital signal processing (DSP) at the receive side.