The case for field-terminated mechanical connectivity

The initial capital expenditures, maintenance costs, and installation speed of fusion splicing hinder its status as the preferred option for FTTH applications. The market has responded by developing a broader array of less costly options that offer the same level of reliability as fusion splicing.

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The drop cable connection serves as a key component in fiber-to-the-home (FTTH) networks. Reliable broadband service depends upon subscriber drops that are stable, efficiently installed, operationally flexible, and affordable. Due to these often contradictory objectives, finding the right connectivity approach for a particular deployment situation can prove to be a daunting task.

Deciding between field-terminated and factory-terminated products is one of the initial choices providers must make before deployment begins. Both alternatives have their pros and cons. Initial capital costs, inventory costs, reliability, deployment speed, cable management, and deployment environment must be considered when identifying the better option.

Over the last several years, the industry has trended away from field termination in favor of factory-terminated products. Factory termination is generally believed to produce a higher performing, more reliable connection than field-terminated connections. The controlled factory termination ensures more consistent end-face geometry, resulting in low insertion loss and attenuation. Factory termination also keeps labor costs low by reducing installation and technician training time compared to field termination.

Conversely, some providers have continued to opt for field-termination methods due to its flexibility and economy. Using factory-terminated products requires an inventory of varying lengths of patch cords for different installation scenarios, whereas field termination uses less expensive bulk cable, which is cut to length on-site. Field termination also eliminates the need to devise slack cable management systems for each installed home – a necessity when using pre-determined lengths of factory-terminated patch cords. And, with factory-terminated products, technicians run the risk of being caught in the field without the proper length of patch cord, causing installation delays and adding to labor costs.

Service providers choosing field-terminated methods of connectivity must then choose between fusion and mechanical splicing. Until recently, the choice was clear. Fusion splicing has been the de facto standard for fiber feeder and distribution construction projects, so the new handheld fusion splicers are considered to be a viable approach for FTTH drop splicing.

However, the initial capital expenditures, maintenance costs, and installation speed of fusion splicing hinder its status as the preferred option. In comparison to mechanical splicing, fusion splicing is expensive. Fusion splicing machines sell for thousands of dollars each, requiring a heavy investment to equip each technician in the field. Additionally, the machines require electrical power, such as a battery, which can deplete of charge in the field, adding time and cost to the process. Moreover, fusion splicing can be time-consuming and requires specially trained technicians, further increasing costs.

The market has responded by developing a broader array of less costly options that offer the same level of reliability as fusion splicing. These options include improved mechanical splicing technology and a new splice-less, gel-free connector.

Reinventing the mechanical splice

A typical mechanical fiber-optic splice consists of a small plastic housing with an aluminum alloy element to precisely align and clamp fibers (Figure 1). An index-matching gel pre-installed at the fiber connection point maintains a low-loss optical interface, which results in a median insertion loss of less than 0.1 dB.

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Figure 1



Mechanical connectors are installed with a simple handheld tool that does not require an electrical power source. Terminating fiber cable using the connectors is fast, easy, and requires little training. A single-fiber termination can be completed in less than three minutes; a no-polish connector that incorporates mechanical splice technology greatly decreases installation time compared to fusion splicing.

Yet, mechanical splicing has not been popular because many providers share a concern that the index-matching gel inside the splices can yellow or dry out, resulting in service failures. However, over the last 20 years, great strides have been made across the industry in improving gel performance and longevity. For example, tests show that the improved gel used in at least one commercially available no-polish mechanical connector performs well in temperatures from -40 to 167 degrees F.

Meanwhile, service providers in Japan have deployed more than 10 million mechanical splices and connectors, both indoors and outdoors. Japan’s service providers are perhaps the world leaders in FTTH deployment, with more than 10 million homes connected. In the past few years, Japanese service providers have completed laboratory and field analyses that affirmed mechanical splicing as a viable long-term answer to outside plant fiber-optic requirements. Mechanical splicing reduced initial tool capital expenditures by 90 percent, doubled splicing speed, and decreased installed costs by 50 percent relative to fusion splicing.

Subsequently, Japanese providers abandoned fusion splicing in favor of full-scale mechanical splicing deployment of the FTTH drop. Field performance has been excellent, with one supplier’s products showing reliability of greater than 99 percent.

Service providers outside of Japan are now beginning to choose mechanical splicing because of its lower total installed cost compared to fusion splicing and its improved reliability. One major U.S. provider reduced its capital expenditure, installation time, and total installation cost by 50 percent when it switched from fusion splices to mechanical splices.

A gel-free alternative
For those who remain steadfast in their resistance to a gel splice, another alternative now exists. An FTTX field-mounted fiber connector that meets indoor and outdoor performance requirements without a splice, gel, or adhesive is now available. Service providers have reduced operating and capital expenditure costs when they replace fusion splices with these new connectors. The equipment savings can be 75 percent or more, and labor savings runs 20 to 50 percent, depending upon the deployment environment.

The splice-less, gel-free connector combines the performance of fusion splice-on connectors with the speed of mechanical splice connectors (see Figure 2). The SC/APC-compatible connector can be installed in indoor or outdoor locations while maintaining optical reflections of less than -60 dB. Test results show that its optical performance remains stable in temperatures of -40 to 167 degrees F. Yet installation is quick and easy, typically taking five minutes or less because an elaborate set up is not required. To install, the fiber is cleaved, inserted through the connector, locked into place with a metal element, and finished with a simple tool. No electrical power is required for installation.

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Figure 2.



In cases where providers prefer field over factory-terminated products, they now have more choices and greater flexibility. Mechanical connectivity methods have advanced to offer highly reliable connections. Whether choosing a product with gel or without, mechanical connectivity provides a cost-effective, reliable alternative for FTTH drop-cable installations.

Jerry Jackson is a marketing development manager for the 3M Communication Markets Division, based in Austin, TX. He holds a master’s degree in mechanical engineering from the University of Texas.

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