Theory and algorithms for fiber-optical intensity channels

Research Project, 2011 – 2013

The aim of this project is to improve the spectral and power efficiencies of affordable short-haul fiber-optical links for use in fiber-to-the home (FTTH) and interconnects (high-speed short links within data centers), where copper wires cannot support the increasing bandwidth demands. The requirement for low-cost optical solutions forces the use of intensity modulation (IM). Very little is known about IM in the bandwidth-limited regime, in contrast to the power-limited regime, where classical formats such as PAM or PPM are applicable. A promising IM technique is subcarrier modulation, in which the data sequence modulates a microwave carrier at 10-100 GHz, which in turn determines the power of the transmitted optical signal. We will design multilevel signal sets for subcarrier modulation and other kinds of bandwidth-limited IM, and we will optimize coding and coded modulation schemes for use with these signal sets. Record-high power efficiencies were obtained already in our rudimentary pilot study 2010. Two kinds of output are expected: (i) fundamental communication theory for IM systems, including tools for signal space analysis, system optimization, and channel capacity estimation; and (ii) practically useful algorithms for transmission in FTTH and optical interconnects, based on realistic channel models and accounting for impairments and affordable complexity. New solutions are expected to increase the data rate and/or reduce the power consumption for these links.