Fiber-optic communication systems constitute the backbone of the communication network infrastructure. The main physical elements of the optical paths in these networks are the optical fiber (as the physical medium for transport) and the optical amplifier (to combat signal attenuation). The transmission bandwidth available over each optical path is enormous, on the order of 10 THz. Despite such a large bandwidth being available, there is a tremendous demand to increase the capacity of fiber-optic communication systems by increasing spectral efficiencies to multiple bits/s/Hz while still maintaining transmission distances on the order of a few thousands of kilometers. Achieving such high spectral efficiency requires using signals with multiple levels in phase and/or amplitude, and possibly using both states of polarization. Transmission of such multilevel signals becomes increasingly impacted by the Kerr fiber nonlinearity, a physical phenomenon unique to the ‘fiber channel’. The Kerr nonlinearity results in signal distortions that rapidly increase with signal power. The question then arises: how to apply Shannon’s information theory to the `fiber channel’ and is there a maximum spectral efficiency associated to the Kerr fiber nonlinearity?

In this talk, we will describe how we applied Shannon’s theory to the `fiber channel’ and present the early results in the direction of conservatively estimating the fiber capacity. A spectral efficiency of ~5 bits/s/Hz (in a single polarization) for transmission over 2000 km in an optically-routed network will be shown to be achievable.

René-Jean Essiambre, Ph.D., is a researcher at Bell Laboratories, Alcatel-Lucent, where he is conducting research on management of fiber nonlinearities and in the design of fiber-optic communication systems. His recent interest includes capacity limits of fiber-optic networks due to fiber nonlinearity, optimization techniques for the design of optical networks, advanced modulation formats, optical phase conjugation and optical regeneration in the context of increasing capacity, reach and functionality of wavelength-division multiplexed communication systems.

Dr. Essiambre has served on the European Conference on Optical Communication (ECOC) and Optical Fiber Communication (OFC) committees. He is a recipient of the 2005 “Engineering Excellence Award” from the Optical Society of America and is Fellow of the same society as well as a senior member of the IEEE. He is currently a Distinguished member of Technical Staff (DMTS) at Bell Laboratories at Alcatel-Lucent.