For the last several months, I’ve been writing about uses for the dark fiber around the country and the world. Last month, I covered delivering broadband to communities, so the logical topic for this month is fiber to the home (FTTH) for broadband delivery.
FTTH is the ultimate solution for broadband, offering almost infinite bandwidth over the cable plant. That means, once a house, apartment or business is connected on fiber, the cabling will be good for decades. FTTH’s other advantage is the reliability of fiber, cutting maintenance costs to virtually nothing.
At the inception of FTTH about a decade ago, it cost approximately $2,500 to connect each home. Today, thanks to new technology, the work of Verizon and Google to reduce costs, and the volume of more than 10 million of homes that have been connected, the cost is now about $500, including labor.
FTTH cost reductions mostly came from passive optical network (PON) system architecture development. Using a passive splitter that allows one fiber port to connect to as many as 64 users, the cost of electronics and the cable plant is divided among all of the users. A PON uses an optical device called a splitter to passively divide a signal going downstream from the service provider to the users and to combine all signals from users coming upstream.
The service provider has a small rack-mounted electronics system called an optical line terminal (OLT) in the central office that can service thousands of users. The OLT connects to the outside world for voice (telephone), data (Internet) and video (TV) over fiber optics. The OLT also connects to the users over a single fiber through a PON splitter to an optical network terminal (ONT) for each user, typically mounted on the side of a house or inside the home or apartment of the user.
The splitter is placed close to the users in a cabinet called a fiber distribution hub (FDH), usually near the sidewalk in a subdivision or urban area and inside the building of an apartment or condo development (which the industry calls a MDU—multidwelling unit). An FDH may contain one or many splitters, depending on the location and size of the FTTH network.
A cable called the “feeder” connects the central office to the FDH. The feeder cable has enough fibers to connect all of the splitters in the FDH to the OLT plus a bunch of extra fibers for spares and future expansion. The feeder cable will be installed either aerially or underground, depending on the location of other cables in the neighborhood.
From the FDH to the user’s ONT, there may be two cables, a multifiber distribution cable serving several users and a single fiber drop cable to the user. The distribution cable is probably spliced into the FDH, but the user end is likely preterminated with a 4-12 fiber outdoor closure that connects to preterminated drop cables.
The use of preterminated cables is a major cost-saving factor because the installer does not have to splice or terminate fibers. It not only saves labor costs, but it also requires practically no expensive installation or test equipment, just a simple cleaning kit and maybe a visual tracer/fault locator.
If the cables are aerial (the cheapest option), the installation is simple: lash the drop cable to the current telephone cable. If the cables have to go underground, it’s still easy if conduit from the street to house is available. Otherwise, the installer will have to find a simple way to install a small cable through the user’s yard. One service provider overseas complained to us that it seemed every user had a flower garden right in the cable’s path.
Once the cable is installed, the ONT is mounted, and the drop cable is connected. The installation tech then spends most of his or her time connecting the telephone, TV and Internet router and checking the operation of each.
In MDUs, the FDH may be in the building, and individual cables are run to each building unit. Sometimes, the network technician will install electronics in the building entrance facility that allows using either the telephone wires (like DSL) or cable TV coaxial to connect to the units. If the ONT is installed in each unit, it is necessary to use small cables with bend-insensitive fiber that can be run unobtrusively along the walls in the building.
In an FTTH PON system, all of the fiber will be single-mode, and connectors are usually SC-APCs (angle-polished physical contact) to prevent reflectance problems on the short fiber runs.
Contractors who build FTTH systems need specialized knowledge and skills, and they need to be able to work under tight schedules and extreme cost constraints.