Many times, we speak with customers who ask us what is RFoG ? We explain that in many cases the losses and potential interference with sending RF signals over long runs of coaxial cable results in inadequate hybrid fiber-coax (HFC) network performance. The reason is that the losses and interference susceptibility for RF coaxial cables used to keep network infrastructure costs reasonable are much greater than glass fiber cables or even higher quality coaxial cables.
A solution to this was provided when the Society of Cable Telecommunication Engineers (SCTE) published the specification for RF over glass fiber (RFoG) in 2010. This enabled the use of single mono-mode fiber to be used instead of coaxial cable for long runs within a Passive Optical Network (PON) or Gigabit Passive Optical Network (GPON). This benefits the delivery of internet and other communication services to homes and businesses, as RFoG is able to use the existing fiber optic network with RF modulated signals to provide downstream bandwidth to 1 GHz. The RFoG standard sets the upstream transmission wavelength to 1550 nm and the downstream transmission frequency to either 1310 nm or 1610 nm. This technology allows for fiber-to-the-home (FTTH) or fiber-to-the-business (FTTB) delivery of communication services using the DOCSIS network, with RFoG transmitter and receiver nodes providing distance coverage of up to 50 km.
RFoG may be used as either a standalone Point to Multi-point (P2M) system or optical overlay for an existing PON/GPON. The RFoG standard is also backwards compatible with some previously existing RF modulation technology, which enables the reuse of existing headend or customer premise equipment (CPE). A RFoG may take one of two architecture types, a passive or hybrid. As a passive, the RFoG system undergoes a 32 split over the industry standard 20 km for a PON with no active devices in the plant. The hybrid RFoG system uses active field optics to conserve the performance or extend the reach of the fiber. Depending on the split ratio, an RFoG system can reach further, or allow for more splits at a lower range.
RFoGs have historically suffered from optical beat interference (OBI), which occurs when two transmitters at the same or similar optical wavelengths transmit simultaneously (a statistical probability event). The more active users on a plant leads to a greater probability of OBI. Though a concern, there are a number of OBI-free systems available that eliminate this risk and enable the expansive rollout of RFoG technology.
So we hope we have given a thorough answer to the question what is RfoG ?
