Capacity Limits of Optical Fiber Networks
15 February 2010
We describe a method to estimate the capacity limit of fiber-optic communication systems (or "fiber channels") based on information theory. The paper is divided into two parts. Part I reviews fundamental concepts of digital communications and information theory. We treat digitization and modulation followed by information theory for discrete memoryless and additive white Gaussian noise (AWGN) channels.
We further evaluate the performance of modulation constellations such as quadrature-amplitude modulation (QAM), combinations of amplitude-shift keying (ASK) and phase-shift keying (PSK), and concentric rings. Part II is devoted specifically to the `fiber channel'. We review the physical phenomena present in transmission over optical fiber networks, including sources of noise, the need for optical filtering, and, most critically, the presence of fiber Kerr nonlinearity.
We describe various transmission scenarios and impairment mitigation techniques over optically-routed networks and define a fiber channel deemed to be the most relevant for communication over such networks. We proceed to evaluate a capacity limit estimate for this fiber channel using ring constellations.
Several scenarios are considered, including uniform and optimized ring constellations, different fiber dispersion maps, and varying transmission distances. We further provide comparisons of this limit with recent record experiments.
