Modulation strategies and phase noise mitigation for spectrally efficient optical coherent communications

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The optical fiber provides an extremely low attenuation, high bandwidth (terahertz) communications media and is the backbone of modern communications networks. The cost per bit of communications has fallen exponentially over past decades, however we are quickly approaching the capacity limits via exploitation of wavelength division multiplexing with coherent detection and higher order modulation. The increasing level of data manipulations in data centres and in local networks, nonetheless, continues to push demand for greater information density on fibers. This proposal applies experimentation, modeling and numerical techniques to research into new modulation strategies in the context of coherent detection systems. The focus will be on spatial multiplexing in fiber with the concomitant cross modal interference and phase noise enhancement. Spatial multiplexing attempts to create new communications channels in the same optical media by exploiting quasi orthogonal channels - quasi because physical imperfections in materials and devices destroy the theoretical orthogonality. Critical analysis of the fiber and multiplexer induced modal correlations must be examined to determine which, if any, of the spatial multiplexing approaches can increase the information bearing capacity of fiber at reasonable complexities for digital signal processing. We will examine the performance of linearly polarized and orbital angular momentum guided modes for spatial multiplexing within the same analytical framework to quantify and elucidate their relative merits. Our long term goals are to develop expertise and experimental facilities for the examination of spatial multiplexing in optical fibers (multiple core fiber, few mode fibers and orbital angular momentum varieties); develop collaboration in design of specialty fibers supporting spatial multiplexing - reconciling systems analysis with design criteria; and to discover niche applications benefiting from spatial multiplexing.