By Venkatesh Mutalik, Staff Engineer, Advanced Fiber-optics, Philips Broadband Networks
Dense Wavelength Division Multiplexing (DWDM) technology has been used in digital communications systems for several years, but its use in analog CATV networks is only recent. Although the components for DWDM technology exist, their use in CATV systems is quite different from that of digital systems, and the requirements are quite often complicated and conflicting.
In general, factors such as number of optical hubs, required bandwidth capacity, transport distances, required RF level differential between the broadcast and narrowcast inputs, choice of return transmission scheme determine the shape and transparency of the envisioned network
Proper analysis of the above · parameters determines the number of optical wavelengths needed, level of transparency of the optical hub, the choice of a proper multiplexing scheme for the return transmission system, and the number of nodes that may be combined on each return DWDM transmitter.
These choices are, in turn, ultimately limited by fiber effects such as Stimulated Raman Scattering (SRS) cross-talk, fiber dispersion, EDFA noise and gain-tilt, and available passive and active component specifications, like DWDM laser chirp.
This paper will examine the state of the art in DWDM technology from a system architectural point of view. The goal of the paper is to explain several competing architectures within the framework of DWDM technology in an effort to insure a cost effective and optimally functional network design.