FIBER OPTICS

Question 1

is essentially a waveguide for light. It consists of a core and cladding that surrounds the core.

Answer 1

Optical Fiber

Question 2

The index of refraction of the cladding is less than that of the
core, causing rays of light leaving the core to be refracted back
into the core

Question 3

can be used for the source of optical fiber

Answer 3

A light-emitting diode (LED) or laser diode (LD)

Question 4

is made from thin strands of either glass or plastic. It has little mechanical strength, so it must be enclosed in a protective jacket. Often, two or more fibers are enclosed in the same cable for increased bandwidth and redundancy in case one of the fibers breaks

Answer 4

Optical Fiber

Question 5

It is also easier to build a full-duplex system using two fibers, one
for transmission in each direction.

Question 6

Optical fibers work on the principle of

Answer 6

Total Internal Reflection

Question 7

With ________, the refractive index is listed

Answer 7

light

Question 8

The angle of refraction at the interface between two media is
governed by

Answer 8

Snell’s law

Question 9

The ________ of the fiber is closely related to the critical
angle and is often used in the specification for optical fiber and
the components that work with it

Answer 9

Numerical Aperture

Question 10

Types of Fiber Optics

Answer 10

1.Single Mode Fiber Optic Cable
2. Multimode Fiber Optic Cable

Question 11

has a small diametral core that allows only one mode of light to propagate. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel further

Answer 11

Single Mode Fiber Optic Cable

Question 12

This application is typically used in
long distance, higher bandwidth runs by Telcos, CATV companies,
and Colleges and Universities

Answer 12

Single Mode Fiber Optic Cable

Question 13

is usually 9/125 in construction. This means
that the core to cladding diameter ratio is 9 microns to 125
microns.

Answer 13

Single Mode Fiber Optic Cable

Question 14

has a large diametral core that allows
multiple modes of light to propagate. Because of this, the number
of light reflections created as the light passes through the core
increases, creating the ability for more data to pass through at a
given time

Answer 14

Multimode Fiber Optic Cable

Question 15

RF broadband signals, such as what cable companies commonly
use, cannot be transmitted over multimode fiber.

Question 16

Because of the high dispersion and attenuation rate with this type
of fiber, the quality of the signal is reduced over long distances.
This application is typically used for short distance, data and
audio/video applications in LANs.

Answer 16

Multimode Fiber Optic Cable

Question 17

is usually 50/125 and 62.5/125 in construction.
This means that the core to cladding diameter ratio is 50 microns
to 125 microns and 62.5 microns to 125 microns.

Answer 17

Multimode Fiber Optic Cable

Question 18

Since optical fiber is a waveguide, light can propagate in a number
of modes. If a fiber is of large diameter, light entering at different angles will excite different modes while narrow fiber may only excite one mode

Question 19

will cause dispersion, which results in
the spreading of pulses and limits the usable bandwidth

Answer 19

Multimode propagation

Question 20

has much less dispersion but is more expensive
to produce. Its small size, together with the fact that its numerical
aperture is smaller than that of multimode fiber, makes it more
difficult to couple to light sources

Answer 20

Single-mode fiber

Question 21

is a fiber where a uniform refractive index exists
within the core and a sharply decreased refractive index exists in
the core-cladding interface because of the lower refractive index
in cladding.

Answer 21

Step-Index Multimode Fiber

Question 22

the light propagates in the shape
of a zigzag along the fiber/core axis according to the principle of
total reflection

Answer 22

Step-Index Multimode Fiber

Question 23

Light entering the fiber at different angles of incidence will go
through different paths. Although the incident lights propagate at the same speed simultaneously at the input, the time to reach the output of the fiber is different, resulting in a temporal dispersion called

Answer 23

modal dispersion

Question 24

Since digital communications use light pulses to transmit signals
down the length of the fiber, the modal dispersion causes the
pulse to widen severely and spread out when they travel along
with the fiber. The more modes the fiber transmits, the more pulses spread out. This significantly limits the bandwidth of step-index multimode fibers.

Question 25

What’s more, the modal dispersion is not good for optical fiber communication as well. For digital optical fiber systems, when the dispersion is serious, it will cause pulses to overlap with each other, causing

Answer 25

inter-symbol interference (ISI) and increasing the bit error rate (BER)

Question 26

is a type of optical fiber where the refractive index is higher at the axis of the core and then it decreases gradually towards the core-cladding interface

Answer 26

Graded-Index Multimode Fiber

Question 27

That is to say, the refractive index of a graded-index fiber gradually decreases from its center, and eventually decreases to the same value as the cladding at the core edge. The change in refractive index causes refraction rather than total internal reflection. When light passes through a layer with a lower refractive index, the light will fold back to the fiber axis.

Question 28

For graded-index multimode fiber, the light travels forward in the form of sinusoidal oscillation. Like step-index multimode fibers, different lights in a gradedindex multimode fiber travel along different paths. However, the speed of light propagation in graded-index multimode fibers is different because the speed of guided light varies with the refractive index of the fiber core.

Question 29

Graded-index fiber has less dispersion than a multimode stepindex fiber.

Question 30

in fiber optics results from the fact that in multimode propagation, the signal travels faster in some modes than it would in others.

Answer 30

Dispersion

Question 31

Single-mode fibers are relatively free from dispersion except for

Answer 31

intramodal dispersion

Question 32

Graded-index fibers reduce dispersion by taking advantage of higher-order modes.

Question 33

One form of intramodal dispersion is called ____________ because it depends upon the material of the core

Answer 33

material dispersion

Question 34

Another form of dispersion is called _________________ Dispersion increases with the bandwidth of the light source

Answer 34

waveguide dispersion

Question 35

in optical fiber result from attenuation in the material itself and from scattering, which causes some light to strike the cladding at less than the critical angle

Answer 35

Losses

Question 36

Bending the optical fiber too sharply can also cause losses by causing some of the light to meet the cladding at less than the critical angle.

Question 37

Types of Losses

Answer 37

- Intrinsic Optical Fiber Losses - Extrinsic Optical Fiber Losses

Question 38

Intrinsic Optical Fiber Losses

Answer 38

- Absorption losses - Dispersion losses - Scattering losses

Question 39

in optical fiber are the major cause of optical fiber losses during the transmission. When the photon interacts with the components of the glass, an electron or metal ions, the light power is absorbed and transferred into other forms of energy like heat, due to molecular resonance and wavelength impurities

Answer 39

Absorption losses

Question 40

are the results of the distortion of optical signal when traveling along the fiber. Dispersion losses in optical fiber can be intermodal or intramodal.

Answer 40

Dispersion losses

Question 41

is the pulse broadening due to the propagation delay differences between modes in multimode fiber

Answer 41

Intermodal dispersion

Question 42

is the pulse spreading in single mode fiber, because the refractive index or the propagation constant varies with wavelength.

Answer 42

Intramodal dispersion

Question 43

in optical fiber are due to microscopic variations in the material density, compositional fluctuations, structural inhomogeneities and manufacturing defects.

Answer 43

Scattering losses

Question 44

is another type of loss in optical fiber. By joining two optical fibers end-to-end, splicing aims to ensure that the light passing through it is almost as strong as the virgin fiber itself.

Answer 44

Fiber optic splicing

Question 45

But no matter how good the splicing is, the splicing loss is inevitable. Fusion splicing losses of multimode fiber are 0.1-0.5 dB, 0.3 dB being a good average value. For single mode fiber, the fusion splicing loss typically can be less than 0.05 dB.

Question 46

are the losses of light power resulting from the insertion of a device in a transmission line or optical fiber

Answer 46

Connector losses or insertion losses in optical fiber

Question 47

is the common problem that can cause optical fiber losses generated by improper fiber optic handling. There are two basic types. One is micro bending, and the other one is macro bending

Answer 47

Bending

Question 48

refers to a large bend in the fiber (with more than a 2mm radius)

Answer 48

Macro bending

Question 49

When measuring the total losses in optical fiber, they also used to calculate the _________, the above-mentioned types of losses should all be considered.

Answer 49

Link Budget

Question 50

introduce the connector performance requirement for each grade of fiber patch cable. These standards guide end users and manufacturers to make best use of optical cables within the regulations

Answer 50

IEC standards

Question 51

According to _________________________, the insertion loss of mated connectors can be categorized in 4 different grades

Answer 51

IEC 61753-1 Attenuation of Random Mated Connectors

Question 52

There are two basic types of fiber-optic cable. The difference is whether the fiber is free to move inside a tube with a diameter much larger than the fiber or is inside a relatively tight-fitting jacket. They are referred to as loose-tube and tight-buffer cables

Question 53

all the stress of cable pulling is taken up by the cable’s strength members and the fiber is free to expand and contract with temperature

Answer 53

Loose-tube cables

Question 54

cheaper and generally easier to use

Answer 54

Tight-buffer cables

Question 55

is ideal for installation in distribution as well as transmission environments, even when live-line installations are required . As its name indicates, there is no support or messenger wire required, so installation is achieved in a single pass, making ADSS an economical and simple means of achieving a fiber optic network .

Answer 55

Loose Tube Type ADSS Cable from Fiberstore

Question 56

isolates the fibers from the cable structure. This is a big advantage in handling thermal and other stresses encountered outdoors, which is why most loose tube fiber optic cables are built for outdoor applications. In outside application, ADSS Cable is the special loose tube cable.

Answer 56

Loose tube structure

Question 57

typically are used for outside-plant installation in aerial, duct and direct-buried applications

Answer 57

Loose-tube cables

Question 58

Structure of a Tight Buffered Cable

Answer 58

1. Outer Jacket (sheath) 2. Aramid Yarn (Kevlar by Dupont) 3. Tight Buffer

Question 59

In fiber-optic systems, the losses from splices and connections can be more than in the cable itself. Losses result from:

Answer 59

* Axial or angular misalignment * Air gaps between the fibers * Rough surfaces at the ends of the fibers

Question 60

Coupling the fiber to sources and detectors creates losses as well, especially when it involves mismatches in numerical aperture or in the size of optical fibers.

Question 61

Good connections are more critical with single-mode fiber, due to its smaller diameter and numerical aperture.

Question 62

A splice is a permanent connection and a connector is removable.

Question 63

As with ______________, it is possible to build power splitters and directional couplers for fiber-optic systems. It is more complex and expensive to do this with fiber than with copper wire.

Answer 63

coaxial cable and microwave waveguides

Question 64

are categorized as either star couples with multiple inputs and outputs or as tees, which have one input and two outputs

Answer 64

Optical couplers

Question 65

A number of fibers can be fused together to make a ______________

Answer 65

transmissive coupler

Question 66

allows a signal entering on any fiber to exit on all other fibers, so the coupler is bidirectional.

Answer 66

reflective coupler

Question 67

operate on the idea that electromagnetic energy can only appear in a discrete amount known as a quantum

Answer 67

Optical emitters

Question 68

These quanta are called __________ when the energy is radiated Energy in one photon varies directly with the frequency

Answer 68

photons

Question 69

is form of junction diode that is operated with forward bias. Instead of generating heat at the PN junction, light is generated and passes through an opening or lens

Answer 69

LED

Question 70

generate coherent, intense light of a very narrow bandwidth and are constructed much like LEDs but operate at higher current levels

Answer 70

Laser diodes

Question 71

The most common optical detector used with fiber-optic systems is the _______

Answer 71

PIN diode

Question 72

is operated in the reverse-bias mode

Answer 72

PIN diode

Question 73

is also operated in the reverse bias mode. The creation of electron-hole pairs due to the absorption of a photon of incoming light may set off avalanche breakdown, creating up to 100 more pairs.

Answer 73

Avalanche Photodiode