OKI Technology Will Extend PON Distance to 100 KM

  • FTTH
  • GEPON
TOKYO - OKI announced the development of an adaptive network configuration technology that allows flexible, low-cost FTTH networks with a 100-kilometer reach.

Despite the rapid advance of FTTH, optical access systems based on current GEPON technology still have a maximum service range of 20 km between the central office and the customer premises. (Another passive optical network (PON) technology, GPON, has an extended-reach capacity of 40 km). Because adding central offices is expensive, networks in sparsely populated regions must use more costly active Ethernet technology - or, more often, rural residents do not receive high-speed broadband at all. Another limit of GEPON is in its ability to respond flexibly to accommodate a growing subscriber base or rapid changes in demand.

To address these issues, Japan's National Institute of Information and Communications Technology commissioned OKI in 2009 to research technologies that would enable the delivery of broadband services without installing new central offices, based on virtualized connections. With support from Japanese incumbent provider NTT, OKI connected NTT East's buildings in three locations with optical fiber, demonstrating the feasibility of a flexible optical access network in a test bed that simulated a total transmission distance of 100 km between central office and subscriber.

The longer reach is achievable by reducing the loss of optical signal in the fiber. According to Takeshi Kamijoh, OKI's general manager of research and development, OKI combined two technologies - optical hybrid filtering and adaptive networking - to reduce the signal loss between the optical line terminals (OLTs) in central offices and optical network units (ONUs) at customer premises.

Optical hybrid filtering adds optical code division multiplexing (OCDM) to wave-division multiplexing (WDM) to achieve filters with low transmission loss. Adaptive networking builds ring or cascade networks by using centralized control node and passive optical hybrid filtering for the PON system. This reduces the loss resulting from branching.

Centralized control nodes switch between WDM and OCDM channel allocation, creating a virtual star network that does not depend on physical connections between OLTs and ONUs. Not only does the network have a longer reach, but if the OLTs in the network include both GEPON and next-generation 10 GEPON, any subscriber can easily upgraded from GEPON to 10 GEPON.

OKI's experiment demonstrated the transmission of WDM and OCDM hybrid optical signals, restoration via passive routing, and service provisioning from GEPON to 10 GEPON without affecting other users. OKI says it plans to continue working on the technology with a view to commercializing it.

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