Digital services using quadrature amplitude modulation (QAM) over CATV analog DWDM system

Abstract

Dense Wavelength Division Multiplexing (DWDM) has recently gained great popularity as it provides a cost effective way to increase the transmission capacity of the existing fiber cable plant. For a long time, Dense WDM was exclusively used for baseband digital applications, predominantly in terrestrial long haul networks and in some cases in metropolitan and enterprise networks. Recently the performance of DWDM components and frequencystabilized lasers has substantially improved, while the costs have come down significantly. This makes a variety of new optical network architectures economically viable. The first commercial 8-wavelength DWDM system designed for Hybrid Fiber Coax (HFC) networks was reported in 1998 [1]. This type of DWDM system utilizes Sub-Carrier Multiplexing (SCM) of Quadrature Amplitude Modulated (QAM) signals to transport IP data, digital video broadcast (in MPEG format) and Video on Demand (VOD) on ITU grid lightwave carriers. The ability of DWDM to provide scaleable transmission capacity in the optical layer with SCM granularity is now considered by many to be the most promising technology for future transport and distribution of broadband multimedia services.