Why mechanical-splice and fusion splice connectors each offer distinct advantages for fiber-to-the-home deployment.
BY JOSEPH HERRIDGE
The drop segment of fiber-to-the-home (FTTH) networks is the most important because it is the link that will actually generate subscriber revenue. It is also arguably the most challenging for carriers. Fiberoptic connector installation at distribution cabinets and subscriber premises must be fast, easy, and dependable to reduce connection time and minimize future service calls.
 FIGURE 1. A typical single-family unit FTTH deployment. |
Four methods of connectivity are prevalent in this network segment: factory-terminated solutions, fusion splice pigtails, mechanical splice connectors and fusion splice field-installable connectors. In single-family unit (SFU) FTTH deployments, connectors are typically used at the fiber service terminal and in optical network terminals (ONTs) at the customer premises (Figure 1).
 FIGURE 2. A typical multi-dwelling unit FTTH deployment. |
In multidwelling unit (MDU) FTTH deployments, connectors can be used in multiple locations, including the basement wiring closet, fiber distribution terminals, and the customer premise ONT (Figure 2).
Unique sets of challenges exist in this last segment of the FTTH network. Each of these scenarios can have different connectivity concerns depending upon whether they are brownfield or greenfield builds, the layout and proximity of the premises being connected, indoor or outdoor, and a host of other considerations. The table highlights some factors to consider when choosing last-mile connectivity options.
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Factory-terminated solutions have proven to be very cost effective for outside-plant installation, but require some engineering and planning. Fusion splice pigtails require additional hardware (splice trays) and increased installation time due to preparation of two cables and fiber routing in the tray. They also require a large up-front investment in splice equipment and training. This leaves the installer with two leading field-installable connector technologies as alternatives for subscriber connectivity in FTTH networks?mechanical-splice connectors and fusion splice connectors. These technologies offer unique advantages, and each has targeted applications based on the skill level of installers, equipment, environment, system performance requirements, and applications.
Mechanical splice connectors
Mechanical splice connectors are most commonly comprised of a factory-polished ferrule containing a fiber stub. The fiber stub is precisely cleaved in the factory and protrudes into the body of the connector, which contains the alignment and splice-activation mechanism, as well as index matching gel (Figure 3).
 FIGURE 3. Inside a mechanical splice connector. |
Index matching gel refers to a silicone-based gel designed to enhance the performance of mechanical splices. The gel is formulated to have an index of refraction, which matches the glass used in optical fibers. The purpose of index matching gel is to reduce the reflectance caused by the gap present between the stub fiber and field fiber when they are joined in a mechanical splice.
Here is a typical installation process for a mechanical splice connector:
- Load the connector body into the mechanical splice installation fixture or tool;
- Prepare the field fiber;
- Cleave the field fiber;
- Insert the cleaved field fiber into the connector;
- Activate the mechanical splice;
- Secure the buffer and/or jacket and/or Kevlar to the connector.
Advantages of mechanical splice connectors are:
- Lower capital investment (no need to buy fusion splicers);
- Lower operator skill level/less training required (compared to fusion splicing);
- No power or specialty batteries required for mechanical splice termination;
- Shortened setup and teardown time;
- Easily installed in any environment without the need for “splicer trailers or tents.”
Fusion splice connectors
Fusion splice connectors are most commonly comprised of a factory-polished ferrule containing a fiber stub. The fiber stub is precisely cleaved in the factory and protrudes into the body (or just behind the body) of the connector in a manner to present the stub to the fusion splicer arc (Figure 4).
 FIGURE 4. Fusion splice connector, with the splice within the ferrule holder assembly (top) and outside an assembled connector (bottom). |
A typical installation process for a fusion splice connector:
- Load the connector body into the fusion splicer;
- Prepare the field fiber;
- Load the prepared fiber into a fiber carrier;
- Cleave the field fiber;
- Insert the cleaved field fiber into the fusion splicer;
- Perform the fusion splice;
- Protect the splice (most commonly using a heat shrink protector);
- Secure the buffer and/or jacket and/or Kevlar to the connector.
Advantages of fusion splice connectors include:
- Utilizes existing capital if the carrier has previously invested in fusion splicers (not all splicers are compatible with all connectors);
- Utilizes trained fusion splice technicians for last-mile FTTx terminations;
- Produces better insertion loss and return loss specifications.
The choice is: Both
Field-installable connectors are a viable alternative to factory-terminated solutions, specifically at the ONT and inside MDUs. With their simple installation methods and factory-quality reliability, field-installable connectors address some of the unique deployment challenges in subscriber connectivity. Mechanical splice and fusion splice connector technologies offer unique advantages, and each has targeted applications based on skill level of installers, equipment, environment, system performance requirements and applications.
JOSEPH HERRIDGE is senior product specialist at Corning Cable Systems.
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