Chapter 11 - Optical Fiber and Cable

 

 

1.      What are the three parts of a fiber optic cable?

@Inner:Core        Middle:Cladding            Outer:Buffer

 

2.      What part of the fiber carries the light?  What part traps light in the core?

@The CORE carries the light and CLADDING traps the light in the core.

 

3.      What is defined by the highest angle at which the light is accepted into the core of the fiber?

      @(NA) Numerical Aperture

 

4.      In multimode fiber, does the light travel faster near the center or the outside of the core?

@In multimode fiber, the light travels faster as it approaches the outside of the core.

 

5.      How many times more is the bandwidth capacity of a multimode graded index cable than a step index cable?

@One hundred times

 

6.      What fiber can support gigabit data rates over long-distances?

@Singlemode fiber can support gigabit data rates over long-distances

 

7.      What two factors cause attenuation?

@The two factors that cause attenuation are: Absorption and Scattering

 

8.      In what wavelength windows do fiber optic systems transmit?

@Fiber optic systems transmit in the windows: 850nm, 1,300nm, and 1,500nm

 

9.      List two types of dispersion.

    1.  Modal

10.    Chromatic

 

11.    What is the main purpose of the fiber optic cable?

@The main purpose of the fiber optic cable is to protect the fiber.

 

12.    What standards must inside cables meet?

@Inside cables must meet all fire code provisions.

 

13.    What does a hybrid cable have?

@A Hybrid cable has both singlemode and multimode.

 

14.    What do you use to pull the fiber cable?

@All fiber optic cables must be pulled by the strength member unless the cable has been    specifically designed to be pulled by the jacket.

 

15.    What cable is used in an environmental air area?

     

16.    Which fiber cable is easy to terminate?

@Breakout cables are easy to terminate.

 

 

17.    The cable that has a gel to prevent water getting to the fiber is called what?

      @The cable that has a gel to prevent water getting to the fiber is called  Loose Tube Cables.

 

18.    Name the cable rating or marking of the fiber cable used in vertical runs.

      @The cable rating or marking of the fiber cable used in vertical runs is OFNR or OFCR.

 

19.    When you do not know the bend radius, what should you use as a “rule of thumb”?

@When you do not know the bend radius, the rule of thumb is assume a bending radius under  tension of twenty times the cable diameters.

 

20.    How may you accomplish a long single pull run?

@If a single run is desired but it is too long, the cable can be pulled from the intermidiate point, despooled into a figure 8, and pulled in the opposite direction.

 

21.    How can you reduce the number of field terminations?

@You can reduce the number of field termination by terminating one end of the cable then pull the unterminated end.

 

Chapter 12 - Fiber Optic Connectors and Splices

 

 

1.      Which is permanent – a splice or a connector?

@Splices are used to connect two fibers in a permanent joint.

 

2.      What characteristics are important for both splices and connectors?

@Low loss, high optical return loss, and repeatability are important characteristics for both splices and connectors.

 

3.      Why are most fiber optic connectors “male”?

@Most fiber optic connectors are "male" since the end of the ferrule must be polished after the fiber is glued into it.

 

4.      What connector ferrule material is used most often?

      @Ceramic ferrules are used most often

 

5.      Why are the new small duplex connectors likely to be popular?

@The new small duplex connectors are likely to be popular because these connectors offer much higher density of fiber optic interfaces in patch panels and networking equipment.

           

6.      Why are multimode connectors installed in the field more often than singlemode connectors?

@Multimode connectors are installed in the field more often than singlemode connectors because the tolerances on a singlemode terminations are much tighter and the polishing processes are more critical, making consistent field termination difficult.

 

7.      Which termination process produces the lowest cost, lowest loss, and most reliable connections?

@Epoxy/Polish  termination process produces the lowest cost, lowest loss, and most reliable connection.

 

8.      To cure the epoxy, you can leave the connector overnight.  Can you use a heat gun for quicker results?

            @No.  A heat gun should never be used to try to cure the epoxy faster, as the uneven heat may not cure all the epoxy or may overheat some of it and prevent it from ever curing.

 

9.      Which connection type -  Hot Melt, crimp/polish, quick-setting adhesives, prepolished/splice – has two splice losses in addition to a connector loss?

      @Prepolished/splice has two splice losses in addition to a connector loss.

 

10.    When should you try to learn new connectors in the field?

      @Never, never, NEVER.  You should never try to learn new connectors in the field.  The field is no place to experiment or learn.

 

 

 

11.    What type of work area should one work in with fiber optic connectors?

@One should try to work in the cleanest possible location when working with fiber optic connectors.

 

12.    Which splice gives the best long-term reliability?

      @Fusion splicing gives the best long-term reliability.

 

13.    When cleaving, you only put a small defect on the fiber and pull carefully to finish the crack;  you never cut through the fiber.  T or F

      @False.  Cleaving is done by using a sharp blade to put a surface defect on the fiber, then pulling carefully to allow a crack to propagate across the fiber.

 

14.    How do you minimize the loss of connectors?

@Loss of connectors is minimized when the two fiber cores are perfectly aligned.

 

15.    With mechanical splices, what can you do to reduce back reflections?

@On mechanical splices, it is possible to reduce back reflection by using index matching gels and non-perpendicular cleaves, which cause back reflections to be absorbed in the cladding of teh fiber.

 

16.    What do you clean connectors with before connection and testing?

@Before connection and testing, it is advisable to clean connectors with lint-free wipes moistened with isopropyl alcohol.

 

17.    What speeds installation and gives better protection to fiber cables?

@Innerduct speeds installation and gives better protection to fiber cables.

 

18.    What is the biggest failure problem with connections inside a building?

@The biggest failure problem with connections inside a building is connectors broken at the back end by people working in communications closets.

Chapter 13 - Fiber Optic Testing

 

 

1.      What instrument is used to test attenuation or loss?

      @Optical power is used to test attenuation or loss.

 

2.      What instrument will verify splice loss?

      @FO power meter and source, test kit, or OLTS (optical loss test set) will verify splice loss.

 

3.      What are the three primary wavelengths used with fiberoptics?

      @850 nm, 1,300 nm, 1,550 nm are the three wavelengths used with fiberoptics.

 

4.      What components make up an end-to-end cable?

      @Splices, couplers, connectors, and intermediate patch panels make up an end-to-end cable.

 

5.      What two specifications must you consider in choosing a power meter?

@The power meter must be chosen to be appropriate to the wavelengths being tested.  For field measurements, a resolutiion of 0.1 dB is appropriate, while lab tests of low loss patchcords may require 0.01 dB resolution.

 

6.      Which fiber and wavelength are most sensitive to stress?

      @Singlemode fiber at 1,550 nm are most sensitive to stress.

 

7.      Which method of caliberation is preferred when testing?

      @The  launch cable reference method is preferred when testing.

 

8.      What does dB stand for, and where is it used?

@dB stands for "decibels" and is used in power meters.

 

9.      What does the “m” in “dBm" represent?

@ 1 milliwatt.

 

10.    What is the anticipated losses of a connector?  A spice?

@The anticipated losses of each connector is:  0.5 dB loss (0.75 maximum).

                                                              splices is:  a loss of 0.2 dB.

 

11.    When using a microscope to check a connector end, what would happen if you were to use a magnification that was too high?

@When using a microscope to check a connector end, Magnification that is too high tends to make small, ignorable faults look worse than they really are.

 

12.    When viewing through a microscope, which direction allows the best inspection?

@Viewing the end of the connector at an angle, while lighting it from the opposite side at approximately the same angle, will allow the best inspection for the quality of polish and possible scratches.

 

13.    Where are scratches or defects on the connector end considered to be a problem?

      @Only defects over the fiber core are a problem.

 

14.    What type of instrument uses backscattering?

@An optical time domain reflectometer (OTDR) uses backscattering.

 

15.    What is the biggest advantage of using an OTDR?

@One of the biggest advantages of using an OTDR is they produce a picture (called a trace or signature) of teh cable being tested.

 

16.    What should one add to the OTDR in order for the receiver to recover from saturation from the test pulse?

@It is common to  use a long fiber called a launch cable or pulse suppressor  between the OTDR and the cables being tested to allow the receiver to recover completely.

 

17.    What would you use to assist an OTDR in finding faults too close for the OTDR resolution?

@A visual fault locator is generally used to assist an OTDR in finding faults too close for the OTDR resolution.

 

18.    Since the OTDR measures the length of the fiber, not the cable, where would you search for a break in a test that showed a break at 15.90 km?

@It is necessary to subtract 1 to 2 percent from the measure length to get the likely cable length. 

You would search for a break at  15.58 km to 15.74 km in a test that showed a break at 15.90 km.

 

19.    What is a “gainer,” and what causes it?

@A gainer is an indication of the difference of backscatter coefficients in the two fibers being spliced.

 

20.    What is the tool called that injects light down a fiber to check the fiber?

      @Visual fiber tracers or fault locators are tools that inject light down a fiber to check the fiber.