Capacity Limits of Information Transport in Fiber-Optic Networks

The instantaneous optical Kerr effect in optical fibers is a nonlinear phenomenon that can impose limits on the ability of fiber-optic communication systems to transport information. We present here a conservative estimate of the “fiber channel” capacity in an optically routed network. We show that the fiber capacity per unit bandwidth for a given distance significantly exceeds current record experimental demonstrations.

Figure 1

Example of a modulated optical field used in this study: (a) Spectrum; (b) symbol realization and constellation; and (c) sampling instants of the corresponding analog waveform. The average power is 1 mW.

Figure 2

Information rate and fiber channel capacity for ring constellations. Right axis: information rate in the absence of fiber nonlinearity; Left axis: fiber capacity when taking into account fiber nonlinearity for a 2000-km system described in the text. A maximum of $\sim 5.6\mathrm{bits}/\mathrm{s}/\mathrm{Hz}$ per polarization state is obtained for 16 rings.

Figure 3

Backrotated constellations after transmission: (a) without ASE (noise) and fiber nonlinearity. Graphs (b), (c), and (d) are with noise and fiber nonlinearity for different SNR. Note that nonlinear distortions tend to spread the constellation points along the modulation circle they belong to.