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Hybrid fiber/coax (HFC) networks with tree-and-branch architecture provide two-way transmission of broadcast analog video channels and interactive digital video/data services via standard single-mode fibers (SMFs) to multiple fiber-nodes. The signals from the master head end to the primary and secondary hubs are transmitted over SMFs typically using 1550 nm externally modulated distributed-feedback (DFB) laser transmitters. These hubs may house synchronous optical network equipment with the associated add-drop multiplexers or some proprietary technology as well as modems, routers, and servers for high-speed data. The optical signals at 1550 nm are converted to RF signals and then back to optical signals for transmission to various optical fiber nodes, typically using 1310 nm directly modulated DFB laser transmitters. The explosive demand for these services, particularly for high-speed data services, has pressured cable TV operators to increase their bandwidth capacity while lowering their network upgrade costs. In the forward path, the bandwidth capacity of the HFC network is sufficiently large to support all the growing demand for these services. In contrast, the return-path bandwidth allocation of HFC networks is not only limited, but also can support only lower modulation formats (for example, lower bandwidth efficiency), caused primarily by ingress noise. Consequently, cable TV operators are forced to modify their network architecture to exploit other technologies to increase return-path bandwidth capacity at lower cost.

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