The Delicate Balance

Choosing Robust Alternatives for Multi-Wavelength Systems

Dr. Timothy Brophy
Director of Network Architectures
Transmission Network Systems
Scientific Atlanta, A Cisco Company

Fernando Villarruel
Systems Engineer
Transmission Network Systems
Scientific Atlanta, A Cisco Company

Dr. Kuang-Yi Wu
Senior Staff Engineer
Transmission Network Systems
Scientific Atlanta, A Cisco Company

Abstract
The potential to more completely exploit the bandwidth available in HFC plants by using multiple wavelengths to carry unique content over a single fi ber is assessed. Initial attempts using CWDM have given way to DWDM in the 1310 band in order to overcome the impairments of widely spaced wavelengths. An examination of the requirements to provide full-band transmitters under the restrictions of fiber non-linearities which go beyond the usual transmitter design constraints leads to tradeoffs among the link distance, optical power, and the number and spacing of the wavelengths in the system. While the fundamental issues arise due to fiber physical considerations, they are mitigated by considering the system as a whole, and modifying or constraining the transmitters, the RF loading, and the passives in the system. Solutions to choosing wavelengths which can successfully carry multiple forward path payloads and yield near single-transmitter performance are presented. Preliminary data indicate substantial improvement relative to CWDM systems and commercially viable product.

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