Fiber to the home

Fiber to the home provides the ultimate customer access technology. Here the fiber-optic cables are extended to the ONU located in the customer's premises. This provides virtually unlimited bandwidth to the customer for all conceivable applications such as provision of video, voice and high-speed data access up to 1 Gbps per customer. FTTH is future-proof, being the only current technology able to meet the demands for such high bandwidth. The basic FTTH architecture is shown in Figure 7.16.

This is a much more expensive option than a HFC because the ONU is required for each customer rather than for a group of up to several hundred customers. FTTH is not cost effective at this time, and is dependent upon advances in technology to provide a more cost-effective bandwidth on fiber-optic cables, and more cost effective ONU technology. The main driver for FTTH will be the requirement for greater bandwidth into the home, since it is the only practical way of providing affordable gigabit data rates to individual customers for the foreseeable future.

Figure 7.16

Basic FTTH architecture

The simplest method of providing FTTH is to use passive 1:N optical splitters to divide the downstream optical bandwidth roughly equally between the N customers. Similarly passive N:1 combiners are used to consolidate their upstream data onto another fiber. The generic term passive optical network (PON) is used to describe these splitter-based FTTH designs. Alternatively, a single fiber can be used for both directions of transmission using wavelength division multiplexing (WDM). This requires the use of bidirectional splitters and combiners. The splitting of the optical power among many customers in a PON has important optical power budget considerations. Using 16 customers per fiber requires approximately 1/16th of the fiber power to be delivered to each customer resulting in approximately 14 dB lower signal than the equivalent FTTC architecture. The splitting losses can be overcome by the use of optical amplifiers before the passive splitter. The challenge here is to maintain a sufficiently large signal-to-noise ratio at the receiver.

An interesting development involving FTTH is the proposal for the creation of a Gigabit national data grid (GNDG) within the United States. This is intended to overcome the bandwidth and traffic limitations of the Internet and meet all conceivable home and business communications requirements for the foreseeable future. The proposal includes the provision of a Gigabit point of presence (GigaPOP) in each of the 465 congressional districts in the country. By connecting these to local fiber loops and spurs in metropolitan areas, over 90% of the country could be within one mile of a GigaPOP. The proposal also allows the use of the alternative access technologies, already discussed, such as xDSL, coax or wireless to provide service at lower data rates. However interfacing to such solutions may well cost nearly as much as the ultimate fiber to the home infrastructure.

Wavelength Division Multiplexing with appropriate splitters/combiners are the main technologies required to implement such a network. Current commercially available WDM systems are capable of providing bandwidths of 40 Gb per fiber, using 16 wavelengths at 2.5 Gbps each. It is expected that these data rates will reach 100 Terabits within the next 10-15 years.

Central Office

Fiber optic cable

Fiber optic cable

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