Questions
1
Describe what bend loss is and steps that can be taken to minimise it in the context of
optical fibre.
2
Describe what type of fibre cable (loose tube or tight jacket) would usually be used in
an outdoor cabling installation stating a reason why.
3
An indoor fibre cable is to be used to connect two floors of a building and is to be
installed vertically in a congested maintenance shaft. What types of protection would
you expect the cable to have?
4
Discuss in detail the advantages / disadvantages of the three main types of fibre
connection, fusion splice, mechanical splice and connectorisation.
5
Give two advantages or disadvantages of a singlemode fibre over a multimode fibre.
6
Describe what type of fibre cable (loose tube or tight jacket) would usually be used in a
building cabling installation stating a reason why.
7
An outdoor fibre cable is to be used to connect two buildings on a campus and is to be
directly buried, what types of protection you would expect the cable to have.
8
Optical fibre cables use two main techniques to protect the optical fibres within them,
describe one of them.
9
(i) Optical fibre cables use two main techniques to protect the optical fibres within
them, describe one of them.
(ii) In Figure 9 is Direct Buried & Under-water optical fiber cable. What types of
protection is the cable giving the optical fibre within it.
Questions
Figure 9
1
0
List 6 advantages and disadvantages of optical fibre and briefly describe.
1
1
In optical fibre telecommunications systems three wavelength windows are typically
used. What are they and in what advantages and disadvantages do they bring to their
respective systems.
1
2
Show how a loss measurement is taken between two patch panels. Use diagrams to
support your answer.
1
3
Describe 3 safety issues in relation to optical fibre systems.
1
4
850nm and 1330nm light sources are typically used in optical fibre building cabling
systems. Why are 1550nm sources typically not used?
1
5
Name three common areas that optical communications are used.
Questions
1
6
Describe in brief how ‘Total internal reflection’ allows light to be guided down an
optical fibre.
1
7
The refractive index of the glass in an optical fibre is an important parameter. What
does refractive index mean?
1
8
If the input power of an optical fibre link is 3mW and the output power is 0.01mw,
what in the attenuation of the fibre link in dB?
2
0
Name one type of fibre attenuation processes and discuss how it works.
2
1
What steps can be taken to reduce Absorption loss in an optical fibre link?
2
2
What types of protection will an optical fibre cable have, to protect the fibres enclosed
from moisture?
2
3
Describe the typical steps required to terminate an optical connector to an optical fibre.
2
4
What is Fresnel loss?
2
5
Describe one form of fibre core misalignment.
Questions
2
6
What advantages do ‘high density’ building cabling connectors bring to an installation?
2
7
How is an optical fibre cleaved? Use diagrams to support your answer.
2
8
What is the main difference between a high end (expensive) cleaver and a low end
(cheap) cleaver?
2
9
Describe the steps in detail in carrying out a fusion splice.
3
0
What is the purpose in a V-groove in a fusion splicer?
3
1
Discuss the advantages and disadvantages between a fusion splice and a mechanical
splice.
3
2
Describe in brief using a diagram to support your answer how an OTDR operates.
3
3
What safety precaution should be taken when working with scrap fibre?
Solutions
1 (a) Bending loss caused by tight cable bends. At such a bend illustrated below the
conditions for total internal reflection are not maintained for some rays. This occurs
because for such rays have angles of incidence to the cladding less than the critical
angle in the vicinity of the bend. Thus optical power is lost into the cladding. Steps that
can be taken to minimise bend loss are
Ensuring the specified minimum bend radius is maintained.
Training installers as to the risks of bendloss
Using suitable cable management to maintain the bend radius.
[10 Marks]
2 (a) A loose tube cable would usually be used in an outdoor installation. Loose tube cables
allow a cable to stretch without damaging the fibre within. Also loose tube cables
usually have a water blocking gel in the tube that will pour out in a vertical installation.
[10 Marks]
3 (a) Any 2
Tensile strength – A strength member to stop the cable being stretched while installed
Moisture ingress – maintenance shaft could have water systems or be humid. No water
blocking gel.
Crush resistance – Weight if other cables. Protection from cable ties.
[10 Marks]
4 (a)
Essay type comparison of details in table below.
Advantages
Disadvantages
Splice
Low loss
Low cost per splice
Initial high cost of fusion splicer
Permanent
Mechanical splice
Semi permanent
Higher loss than fusion splice
Lower loss than connector
Higher cost per splice
Low equipment cost
Solutions
Connector
Removable
Highest loss
High cost per connector
[10 Marks]
5 (a) Any two of the below.
Advantages
-Higher bandwidth
-Lower dispersion
-Better upgrade potential
Disadvantages
-Difficult to couple light
-Connectorisation, splicing more difficult and expensive
-Connecting equipment more expensive
[10 Marks]
6 (a) A tight jacket cable would usually be used in a building installation. Tight jacket cables
are capable of tighter bend radii than loose tube cables. Also loose tube cables usually
have a water blocking gel in the tube that will pour out in a vertical installation.
[10 Marks]
7 (a) Tensile strength – A strength member to stop the cable being stretched while installed
Crush resistance – To stop the weight of the soil damaging the fibre.
Moisture ingress – To stop water coming in contact with the fibre and causing it to fail.
[10 Marks]
8 (a) Loose tube or tight jacket.
[10 Marks]
9 (a) Any 2
Tensile strength – A strength member to stop the cable being stretched while installed
Moisture ingress – Has an aluminium foil jacket. As it is loose tube will also have
moisture blocking gel.
Crush resistance – Has a wire braid jacket just below the first layer of the cables outer
jacket.
[10 Marks]