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Loss is the No. 1 performance specification in fiber optics. Whether you are designing a network, specifying components or testing an installation, the focus is on loss. How well do you understand fiber optic loss? Answers and explanations are in red.
1. Loss in a fiber optic cable plant is the reduction in optical power caused by ________.
B. Fiber attenuation
C. Stress on a cable
D. All of the above
The total loss of a cable plant will include the attenuation of the fiber and losses in connections and splices. It may include any stress losses induced in installation.
2. A single connector has no loss. Loss is defined as the light lost when two fibers are joined by two connectors.
3. The attenuation or loss/length of single-mode optical fiber is ________ at longer wavelengths, so long-distance networks are optimized for 1,550 nm transmission.
C. The same
Attenuation of optical fiber is lower at longer wavelengths so the longest links use the longest wavelengths to get the lowest loss of the cable plant.
4. The biggest factor in testing multimode fiber accurately is ________.
A. Source wavelength
B. Mode power distribution
C. Setting a “0 dB” reference
D. Power meter calibration
Mode power distribution must be controlled to get accurate, repeatable measurements.
5. Standards allow fiber optic connectors to have as much as ________ loss.
A. 0.25 dB
B. 0.50 dB
C. 0.75 dB
D. 1.00 dB
Most current standards like TIA 568 allow connectors to have a maximum loss of 0.75 dB to accommodate higher loss connectors like prepolished/splice types.
6. Properly installed adhesive polish fiber optic connectors should really have much lower loss than the worst-case value allowed by the standards.
The standards are written around worst-case connector losses, so adhesive/polish connectors should have much lower losses than 0.75 dB.
7. The lowest loss joints between two fibers can generally be made with ________.
A. SC connectors
B. LC connectors
C. Mechanical splices
D. Fusion splices
Fusion splices weld two fibers together to have the lowest loss. They also have the least reflectance and are the most reliable fiber joining method.
8. Every fiber optic communications system has a(n) ________ loss it can tolerate in the installed cable plant.
C. Minimum and maximum
For any communication system, it needs to have just the right amount of power at the receiver, neither too much or too little. This means it can tolerate cable plant loss in a range. If the loss is too little, the power will be too high so an attenuator is used at the receiver to lower power levels.
9. To calculate a loss budget for the cable plant, one must include the ________.
A. Total loss of all connections
B. Total loss of all splices
C. Total attenuation of the entire fiber length
D. All of the above
As we noted in question 1, the loss of the cable plant includes all these factors, so they must be included in calculating the loss budget.
10. When testing a fiber optic cable plant to see if it is installed properly, you should compare the measured loss to the ________.
A. Calculated loss budget
B. Communications system maximum loss
C. Communications system minimum loss
D. Connector losses
The loss budget calculated in the design phase is the expected loss of the cable plant and should be used to compare the test results of every fiber.
HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.jimhayes.com.