What is fiber to the home (FTTH)? - Structure and components

FTTH Networks Architecture

There are two types of FTTH architecture categories Active Optical Network (AON) and Passive Optical Network (PON).

At this point you would ask, is there’s a difference?

According to the Fiber Optic Association, Active Optical Networks are the easiest way to connect homes with fiber, because

Fiber connects homes to the ISP. But, although it provides the maximum amount of bandwidth, it tends to be expensive because it requires every home to have a dedicated fiber.

Instead, Passive Optical Networks make it possible to share expensive fiber components due to the use of splitters, which divide an input and allows to broadcast services to several homes.

Therefore, PON architecture offer more advantages because a single shared optical fiber can support multiple users.

FTTH Network Equipment

FTTH deployments require a lot of planning and elements to expand from the Access Node to the subscribers’ premises.

In a fiber optic network there are two basic elements:

An Optical Line Terminal (OTL) located at the ISP side and an Optical Network Unit (ONU) placed at the customer’s premises.

The connection between these two elements is made with both optical and non-optical equipment and components.

Non-optical equipment consists in

· Hardware

· Cabinets

· Patch panels

· Fiber closures

· Pedals

And when it comes to optical components we are talking about splices, couplers and adapters, connectors, fiber cables, connectors, splitters, patch cords, drop cables and drop terminals.

Passive equipment

Fiber cables

Installing fiber optic cables is one of the most expensive procedures when deploying a PON Network. Cable installation can be underground (burial), inside ducts and on poles and towers (aerial).

Splitters

According to the Fiber Optics Association, these passive elements take an input and divide it to send the signal to several users, which dramatically reduces costs.

Connectors

Simplex connectors are the most used in FTTH deployments.

The most common used are:

· SC/APC

· ST/APC

· LC/APC

Multifiber connectors are also acquiring popularity, because they can hold from 4 to 72 fibers at the same time, being the MTO the most popular one.

The most common connector type used in PON network is APC (Angle Physical Contact) connector, because its eight degree polished ferrule minimizes loss:

· Return loss: -60 dB.

· Typical loss: 0.5 dB.

Which avoid transmission problems. APC connectors can be certainly identified by their green color

But how do fiber connectors mate?

For fiber optic connectors to mate between each other they need couplers, also called adapters, these elements come in several versions allowing to connect simplex or duplex cables.

Fiber optic couplers are also designed for multimode and single mode cables and are generally used to connect cables with similar connectors

· SC/APC to SC/APC

· ST/APC to ST/APC

· LC/APC to LC/APC.

But hybrid fiber optic couplers accept dissimilar connectors, so you can mate:

· SC/APC to ST/APC.

· SC/APC to LC/APC

· LC/APC to LC/APC and so on.

Fiber optic coupler types are as diverse as fiber optic connectors. They can be FC, LC, SC, ST and MT-RJ and they also have different colors according to how the connector ferrule is polished:

· Green is for APC.

· Blue is for single mode PC and UPC.

· Beige is for multimode PC and UPC.

As with connectors, SC/APC couplers along with ST/APC and LC/APC are the most used fiber optic couplers in FTTH passive optical networks.

FTTH boxes

The FTTH council points out that when it comes to premises (houses, large and small businesses) drop cables typically terminate onto the structure and externally route to a termination box.

Termination boxes are equipped with:

· Splice trays: Let fibers from outdoor cables to be spliced to pigtails that then will be connected with the Optical Network Unit (ONU), the point where the passive network ends and the active equipment is installed.

· Fiber optic couplers to allow the connection.

Beyondtech supplies couplers in simplex and duplex style for single mode and multimode applications. SC/APC couplers are one of the most reliable kind of adapters, which is why they are broadly used in LAN, WAN and CATV systems besides FTTH.