Focus On Fiber Optic Link Loss
We know that, no natter what component you use, there must insertion loss in your fiber optic cabling. Therefore, in order to make your fiber optic cabling system perform at high level, calculating the amount of insertion loss before cable plant is necessary. This article will focus on fiber optic link loss.
The link loss and link loss budget are measured in dB. Link loss is the total insertion loss of all optical components in an optical network. While link loss budget is the amount of loss that a cable plant should have. It is calculated by adding the average losses of all the components used in the cable plant to get the total estimated end-to-end loss. The link loss budget has two important functions: during the design stage to ensure the cabling being designed will work with the links intended to be used over it and; after installation, comparing the calculated link loss to test results to ensure the cable plant is installed properly.
Usually, the loss of four parts need to be calculated: mated pair connector loss, fiber optic splicing loss, fiber optic cable loss and other loss.
- Mated Pair Connector—EIA/TIA 568 standard allows 0.75 max per connector
Connector or “connection” loss is the total loss of the mated pair connectors. It’s standard to assume a 0.3 dB loss for most ultras polished connectors. In order to measure the loss of the connectors, you must mate them with similar connectors, or you are likely to experience different losses. Also, a high quality connector is required when testing matted pairs.
- Fiber Optic Splicing—EIA/TIA 568 max loss is 0.3 dB per splice
According to the Fiber Optic Association (FOA), multimode splices are commonly made using mechanical splices. Best construction practices dictate that even with multimode fiber fusion splicing is ideal. Both forms of splicing generally result in satisfactory results, however fusion splicing proves to be more reliable in adverse surroundings. Single mode fibers that have been fusion spliced will typically have less than 0.10 dB loss. A good average for a skilled installer is generally around 0.05 dB loss.
- Fiber Optic Cable
EIA/TIA 568 spec for multimode fiber is 3.5 dB/ km at 850 nm and 1 .5 dB/km at 1310 nm. This specification translates into a loss of approximately 0.1 dB per 100 feet for 850 nm, 0.046. dB per 100 feet for 1300 nm. For example, 300 ft multimode fiber optic cable at 850 nm would approximately equal 0.3 dB loss. While for single mode fiber, the loss is 0.5 dB per km at 1310 nm, 0.4 dB per km for 1550 nm.
- Other Loss—Passive Components and Margin
Don’t forget to count any other passive components you are using in your network. For example, if you are using splitters or filters, add the insertion loss for those components. In addition, it is recommended to add margin to your link loss calculation to adjust for any unforeseen losses. The amount may vary by designer or application but typically 2-3 dB will allow for sufficient headroom in you network link loss calculation.
The fiber optic link loss calculation and analysis are vital in cable plant. After the cable plant is installed, the calculated loss values are compared with the test results to ensure the link can operate properly. Besides, to reduce the link loss, high quality components are required. Quality is everything when gigabit and higher speeds are required.
