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Functional Requirements Of A Fiber Distribution System: Splicing

Fiber Optic
Posted by James Donovan on 26 October 2016 Connect with James on LinkedIn Estimated reading time: 4 minutes

Splicing:

Splicing in fiber optics is the physical joining of two separate optical fibers with the goal of having 100-percent signal transfer. Splicing connections are meant to be permanent, non-reconfigurable connections.

There are two basic splicing methods in use today: mechanical and fusion (see Figure 1) below:

splicing-figure-1

[figure 1]

Mechanical Splicing

Mechanical splicing involves the use of an alignment fixture to bring and hold two fibers in alignment. Mechanical splices typically give insertion loss values of <0.15dB with return loss values of >35dB and involve the use of an index-matching gel.

Fusion Splicing

Fusion splicing uses an electric arc to “weld” two fibers together. Fusion splices typically have insertion loss values of <0.05dB and return loss values of >70dB.

Whichever splicing type is used, the ODF needs to provide a location to store and protect the splices. The splicing function can be performed on the ODF (on-frame splicing) or in a location near the place at which the OSP cables enter the building, such as the cable vault (off-frame splicing).

Storage: Splice Tray

In either situation, the splice enclosure or panel provides a location to store all splices safely and efficiently. The individual splices are housed within a splice tray, generally holding between 12 and 24 splices.

The splice trays in turn are housed within a panel that accommodates between 96 and 192 splices. Large splice enclosures can generally house up to 864 splices in a single unit. For splice enclosures/panels, the most critical fiber cable management features are bend radius and physical protection.

The fiber cable management within the splice enclosure/panel and the splice tray contributes to the long-term reliability of the fiber network and determines the ability to reconfigure or rework any splices. In routing fibers between the enclosure/panel entrance point and the splice tray, enough slack should be provided and made easily accessible for the technicians to perform any necessary re-splices.

Access to the splice tray

In accessing a splice tray, the technician should move as few installed fibers as possible. Moving fibers routed to the splice trays will increase the time required for the splicing functions as well as the probability of causing a failure within the system.Each splice tray needs a sufficient amount of slack fiber stored around it to allow the tray to be easily moved between one and three meters from the splice panel.

This ensures that the splice technician can do any work in a proper position and work environment. If the splice technician has to struggle to gain access to the service loop for the splices, the probability of the technician’s damaging another fiber is greatly increased, and the probability of the technician properly performing the assigned duties is reduced. In the splice trays, proper bend radius protection also needs to be observed.

Aside from the points mentioned previously regarding fiber breakage and attenuation, a sharp bend within the splice tray near the splice will put added strain on the splice, increasing the possibility of a failure in the splice.

Fusion splices have a higher probability of failing if added stress is put on the splice by a sharp bend before the splice.

Incorporating optical components

As networks grow and technologies change, the ability to add optical splitters, wavelength division multiplexers (WDMs), optical switches and other opto-mechanical products to the ODF becomes more important.

These devices should be easily, safely and economically integrated into the ODF. One type of passive optical component, the optical splitter, is used in networks for serving multiple nodes from one transmitter. This equipment allows fewer transmitters to be used in the network, greatly reducing system costs. Splitters are also used in local and long distance networks to allow non-intrusive network monitoring.

This non-intrusive access allows an active signal to be monitored without interrupting or rerouting service to spare facilities, greatly reducing the time required to perform testing procedures and troubleshooting.

splicing-figure-2

[figure 2]

WDMs are being used to increase the bandwidth of installed OSP fiber. For example, a 16-channel dense wavelength division multiplexer (DWDM) can increase a single fiber’s bandwidth capacity 16-fold. WDMs can also be used in conjunction with optical time domain reflectometers (OTDR) to perform out-of-band testing (testing on one wavelength, operation on another) on active fibers.

The use of OTDRs for out-of-band testing allows for very fast and efficient troubleshooting of fiber networks, as well as the ability to detect problems before they become service-affecting.

Protection as an important consideration

Whatever the optical components, or the means by which they are incorporated into the fiber

distribution system, they need to be properly protected. Bend radius protection and physical protection are the most important considerations for these devices.

Following proper fiber cable management practices in incorporating these devices will reduce the cost of network installation, and network reconfigurations, while improving network reliability.

Learn more

To learn more about fusion splicing and external plant termination into housings explore our Fiber Optic Infrastructure Specialist Training Certification Course.