Drop Cable and Its Termination in FTTH

by www.fiber-mart.com

FTTH (fiber to the home) networks are installed in many areas covering indoor section, outdoor section, as well as the transition in between. To fulfill the cabling requirements from different areas, different types of fiber optic cable are well developed. Drop cable as an important part of FTTH network forms the final external link between the subscriber and the feeder cable. This blog post will focus on this special outdoor fiber optic cable.

 

The Basic of FTTH Drop Cable

Drop cables, as previously mentioned, are located on the subscriber end to connect the terminal of a distribution cable to a subscriber’s premises. They are typicality small diameter, low fiber count cables with limited unsupported span lengths, which can be installed aerially, underground or buried. As it is used in outdoor, drop cable shall have a minimum pull strength of 1335 Newtons according to the industry standard. Drop cables are available in many different types. The following part introduces three most commonly used drop cables divided according to the cable structure.

 

Flat Type Drop Cable, also known as flat drop cable, with a flat out-looking, usually consists of a polyethylene jacket, several fibers and two dielectric strength members to give high crush resistance. Drop cable usually contains one or two fibers, however, drop cable with fiber counts up to 12 or more is also available now. The following picture shows the cross section of a flat drop cable with 2 fibers.

 

Figure-8 Aerial Drop Cable is self-supporting cable, with the cable fixed to a steel wire, designed for easy and economical aerial installation for outdoor applications. This type of drop cable is fixed to a steel wire as showed in the following picture. Typical fiber counts of figure-8 Drop Cable are 2 to 48. Tensile load is typically 6000 Newtons.

 

Round Drop Cable usually contains a single bend-insensitive fiber buffered and surrounded by dielectric strength members and an outer jacket, which can provide durability and reliability in the drop segment of the network. The following shows the cross section of a round drop cable with one tight buffered optical fiber.

 

Drop Cable Connectivity Method: Splice or Connector?

It’s necessary to choose a right architecture for FTTH network from overall. However, drop cable as the final connection from the fiber optic network to customer premises also plays an important role. Thus, finding a flexible, efficient and economical drop cable connectivity method becomes a crucial part of broadband service. Whether to use a fiber optic connector, which can be easily mated and un-mated by hand or a splice, which is a permanent joint? The following will offer the answer and the solutions for your applications.

 

It is known that splice, which eliminates the possibility of the connection point becoming damaged or dirty with a permanent joint, has better optical performance than fiber optic connector. However, splice lack of operational flexibility compared with fiber optic connector. Fiber optic connector can provide an access point for networking testing which cannot be provided by splicing. Both methods have their own pros and cons.

 

Generally, splice is recommended for drop cables in the places where no future fiber rearrangement is necessary, like a greenfield, new construction application where the service provider can easily install all of the drop cables. Fiber optic connector is appropriate for applications which flexibility is required, like ONTs which have a connector interface.

 

Choosing the Right Splice Method

For splice, there are two methods, one is fusion splicing, the other is mechanical splicing. Fusion splicers have been proved to provide a high quality splice with low insertion loss and reflection. However, the initial capital expenditures, maintenance costs and slow installation speed of fusion splicing hinder its status as the preferred solution in many cases. Mechanical splicing are widely used in FTTH drop cable installation in countries, as a mechanical splice can be finished in the field by hand using simple hand tools and cheap mechanical splicer (showed in the following picture) within 2 minutes. It’s a commonly used method in many places, like China, Japan and Korea. However, in US mechanical splicing is not popular.

 

Choosing the Right Connector

For fiber optic connector, there are two types connector for drop cable connection. Field terminated connector, which contains fuse-on connector and mechanical connector, and pre-terminated drop cable, which is factory terminated with connector on the end of drop cable.

 

Fuse-on connector uses the same technology as fusion splicing to provide the high optical connection performance. However, it requires expensive equipment and highly trained technician, and more time like fusion splicing. Mechanical connector could be a replacement of fuse-on connector (showed in the following picture), if the conditions do not fit the mentioned ones. It could be a time-save and cost-save solution for drop cable termination.

 

If you have no limits in cost and want high performance termination in a time-save way, pre-terminated drop cable could be your choice. Many factories can provide you customized drop cables in various fiber types, fiber optic connector and lengths.

 

Conclusion

Customer demand for higher bandwidth will continue to drive the development of FTTH as well as its key component like drop cable. Choosing the right drop cable and drop cable termination method is as important as choosing the right network architecture in FTTH.