When deploying a FTTH network, subscribers must choose the right drop cable interconnect solution. So they need to decide whether to use splices (permanent joint) or connectors (easily mated and unmated by hand) for the best solution. This is for both ends of the drop cable—the distribution point and at the home’s optical network terminal (ONT) or network interface device (NID). Splices and connectors are widely used at the distribution point, while at the ONT/NID, a field-terminated connector or a spliced-on factory-terminated connector is used. This paper discusses the available interconnect solutions (splices and connectors) for FTTH drop cables and their own pros and cons.
Excellent optical performance is the most significant advantage of splices. And splicing can also eliminate the possibility of the interconnection point becoming dirty or damaged, potentially compromising signal integrity, as may happen to a connector end face when it is being handled while unmated. Contaminants will cause high optical loss or even permanently damage the connector end face. Splice enables a transition from 250µm drop cable to jacketed cable.
The major drawback of splice is its lack of operational flexibility. To reconfigure a drop at the distribution point (in the case of one subscriber dropping FTTH service and another one adding it) one splice must be removed, fibers rearranged, and two new fibers spliced. Then it requires the technician to carry special splicing tools for simple subscriber changes. Moreover, other customers’ service may be disrupted by the fiber-handling process. 250µm fiber cable is usually used at the distribution point, which is easily bent and then cause high optical loss or even break the fiber. If a splice is used at the ONT, a tray is needed to hold and protect the splice, which increase the ONT size and potentially the cost.
According to above description, splice is appropriate for drops where there is no need for future fiber rearrangement, typically in a greenfield or new construction application where all of the drop cables could be easily installed during the living unit construction.
Due to the characteristic of being mated and unmated repeatedly, connectors can provide greater network flexibility. Without any tools, a technician can easily connect or disconnect subscribers. Connector could also provide an access point for networking testing.
Material cost is the connector’s most obvious downside. They cost more than splices, although network rearrangement is much cheaper. So providers need weight the connector’s material cost and its potential for contamination and damage against the greater flexibility and lower network management expense.
Connectors could be used to connect different subscribers as needed for distribution points. It must be installed at the ONT and then offers flexibility both at the curb and at the home.
Once the decision goes to splices, the type of splicing (fusion and mechanical) must be determined.
Fusion splicing has been the de facto standard for fiber feeder and distribution construction networks. Fusion splicer is used for FTTH drop splicing as it provides a high quality splice with low insertion loss and reflection (see the picture below). However, the initial capital expenditures, maintenance costs and slow installation speed of fusion splicing hinder its status as the preferred solution. Fusion splicing is best suited for companies which have invested in fusion splicing equipment and have no need to purchase additional splicing machines.
Mechanical splices are successfully deployed around the world in FTTH installation, but not popular in United States because the index matching gel inside the splices can yellow or dry out, resulting in service failures. Great strides have been made in improving gel performance and longevity over the last 20 years.
Once choosing to use a connector, a factory-terminated or field-terminated connector must be decided.
Factory-terminated drop cables provides high-performing and reliable connections with low optical loss. By reducing installation time, factory termination keeps labor costs low. However, factory-terminated cables are expensive compared to field-terminated alternatives. And they require a cable management system to store slack cable at the curb or in home.
The installation of field-terminated connectors can be customized by using a reel of cable and connectors. Fuse-on connectors use the same technology as fusion splicing to provide the highest level of optical performance in a field-terminated connector. Mechanical connectors provide alternatives to fuse-on connectors for field installation of drop cables.
Depending upon service provider requirements and living unit configurations, a hybrid solution of a field-terminated connector on one end of the drop cable and a factory-terminated connector on the other may be the optimal solution.
The drop cable interconnect solution is a key component of a FTTH network. Selecting the right connectivity product not only offers cost savings and efficient deployment but also provides reliable service to customers. Most FTTH drop cable installations have been field terminated on both ends of the cable with mechanical connectivity solutions.