Close Enough?

When designing, building, testing or operating a fiber optic network, is “close enough” good enough?

1. In a fiber optic network design, the loss budget for the cable plant and the power budget for the fiber optic link for the application are both 5 decibels (dB). Will it work?

Correct Answer: Whoa! No margin at all? That’s asking for trouble.

2. You need 10 kilometers (km) of cable for the outside plant link you are installing, and you have three splice points. You use an optical time-domain reflectometer (OTDR) on the spool of cable you have and find it is exactly 10 km. Is that enough?

Correct Answer: No, for all of the above reasons.

3. You tested the loss of a fiber optic cable plant at 2.15 dB, but the loss budget for that cable was only 2.00 dB. What do you do?

Correct Answer: Inspect and clean the connectors, and test again.

4. After you cleaned the connectors on that cable plant, the loss dropped to 2.05 dB. That’s within the margin of error of the measurement, so it is OK to pass that cable.

Correct Answer: True

5. In an electronics upgrade to an old fiber optic cable plant that uses 62.5/125 micron fiber, you realize you only have 50/125 micron patchcords. What can you do?

Correct Answer: Check the power budget because you might have enough margin.

6. At the job site, you realize you are terminating multimode fiber with the adhesive/polish method but only have single-mode connectors. Is that OK?

Correct Answer: Maybe, single-mode connectors have a smaller hole for the fiber.

7. As you prepare to terminate these connectors, you notice the adhesive you have been using for a while is out of date by almost a year. Do you use it anyway?

Correct Answer: No way, it’s too critical to take that risk.

8. That 20-km cable plant you are testing with an OTDR shows about a third of all the splices are gainers. What can you do?

Correct Answer: Test in the opposite direction to average the splice loss. Gainers are not a reason to fail tests.

9. You are estimating a fiber optic cable plant for a bid. How many extra components do you figure into the price?

Correct Answer: 12–15 percent

10. Over the course of the day, you worry because loss test results on a high fiber count cable keep getting higher. What could cause this?

Correct Answer: Any or all of the above