Towards the Shannon Limit of Spectral Efficiency

Progress in high capacity optical communication systems in the year 2010 is reviewed, with spectral efficiency as the main figure-of-merit. Advanced modulation formats, such as quadrature-amplitude-modulation (QAM) and orthogonal-frequency-division-multiplexing (OFDM), together with polarization-division-multiplexing (PDM) and digital coherent detection, are playing key roles in approaching the Shannon limit of spectral efficiency for optical fiber communication. Photonics is now entering into a new era of high spectral efficiency on par with electronics (wireless), yet with orders of magnitude higher overall system capacity.