For decades, industry standards have set the maximum loss of a fiber optic connector at 0.75 decibels (dB). Now this value is being reconsidered since it is unacceptable for the latest high-speed multimode links or single-mode connectors. Let’s test your knowledge of fiber optic connector loss. Correct answers and explanations are in red.
1. The original limit of 0.75 dB for a fiber optic connector loss was set because ________.
A. A 1-dB loss was considered much too large
B. It was an average loss for a good factory-made connector of the time
C. It was a value that any installer could meet
D. It was a compromise to allow inclusion of prepolished/splice connectors
Prepolished/splice connectors were higher loss than adhesive/polish versions but most could meet the 0.75 dB loss value.
2. A typical factory-made or field-installed multimode connector should have a loss of ________ dB.
Multimode connectors may have losses in the range of 0.1-0.5 dB depending on the connector style, termination type and fiber specifications.
3. A typical factory-made single-mode connector should have a loss of ________ dB.
Singlemode connectors and fibers have tighter tolerances than multimode components and are usually only factory terminated, so they typically have lower loss than multimode connectors.
4. Single-mode connectors are generally installed in the field by splicing a pigtail or prepolished connector onto each fiber.
Singlemode connectors are hard to install directly on a fiber in the field so splicing pigtails or prepolished/splice connectors are preferred.
5. Factory-terminated cables use ________ style connector termination.
Epoxy/polish connectors are used for factory terminations because they provide the lowest loss, highest reliability and least cost.
6. Fiber optic connector loss can be tested by either mating a connector on a cable to a known good connector or cutting a fiber optic cable and installing two connectors.
Either method may be used; the first is used primarily for testing terminated cables while the second is used by connector manufacturers to qualify their connectors and provide a specification of average loss.
7. The loss of an individual connector on a patch cable or cable plant is measured by ________.
A. A light source and power meter with one reference cable
B. A light source and power meter with two reference cables
C. An optical time-domain reflectometer (OTDR) with no reference cable
D. An OTDR with two reference cables
Testing a single connector uses a single-ended test with one reference cable, covered in TIA FOTP-171.
8. With several connections in a multi-mode cable plant, the connections farther away from the transmitter or test source will have ________ loss.
C. The same
In multimode cable plants, connectors strip off the higher order modes (mode filtering), so the next connector in a link is joining fibers with less mode fill and will therefore have lower loss.
9. If you measure the loss of a connection with an OTDR in both directions and get different losses, even a gain in one direction, this tells you ________.
A. One connector is improperly polished
B. These are APC connectors
C. Only one connector is prepolished
D. The two fibers mated in this connection have different backscatter coefficients
Since the OTDR uses the backscatter from the fiber to create a snapshot of the link, fibers with different backscatter coefficients will have different connection loss measurements when the direction is reversed.
10. If you have a connector that shows different losses in each direction on OTDR tests, you can ________ to get the best estimate of the actual loss.
A. Average the losses from both directions
B. Use the higher loss
C. Use the lower loss
D. Retest with a different OTDR
The two readings can be averaged to give a good estimate of the actual loss as the fiber differences cancel out in the average.
HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.jimhayes.com.