J2LT4 Fiber-Optic Flashcards
What are the 4 main components of a basic fiber-optic system?
Transmitter
Fiber-optic cable
Optical Connectors
Receiver
LT4 PG.85
What is the purpose of fiber-optic?
To transmit data from one location to another using light.
LT4 PG.85
What is the purpose of the transmitter?
To convert an electrical signal in to a light signal.
LT4 PG.85
How does the transmitter convert an electrical signal to a light signal?
By using a drive circuit to convert the input signal in to a form that will operate the optical source, the optical source then converts that to light.
LT4 PG.85
What would be an optical source in a transmitter?
A light-emitting diode (LED) or laser
LT4 PG.85
What is the basic construction of optical fiber?
Inner core - carries the light
Cladding - reflective covering placed over the core
Buffer - protective coating for the cable
LT4 PG.85
The most widely used fibers are constructed of _____.
Glass
LT4 PG.85
When losses are not a concern in short communication runs, fibers may be constructed from ____.
Plastic
LT4 PG.85
The purpose of optical connectors is?
To terminate the fiber at the transmitter / receiver with as few power losses as possible.
LT4 PG.85
The purpose of the receiver is to?
To accept the light signal and convert it back in to an electrical signal.
LT4 PG.86
What components does a receiver consist of?
An optical detector to convert light signals in to electrical signals and the electronic circuitry needed to amplify the output signal.
LT4 PG.86
Light is commonly expressed as a wavelength in _____.
Nanometers.
LT4 PG.86
What is the range in nanometers of visible light?
380 nm to 780 nm.
LT4 PG.86
Most fiber-optic systems use infrared light, what is the wavelength range of infrared light?
800 nm to 1500 nm.
LT4 PG.86
Refraction plays an important part in the design of fiber-optic cables. What is it and how does it happen?
The bending of light. As light travels from one material to another, it changes velocity which results in the light changing its direction/angle of travel.
LT4 PG.86
What is a photon?
A light particle, similar to an electron.
It represents a certain amount of energy and is used to determine the wavelength of light.
LT4 PG.86
A high range of transmission frequencies is called….
Wide bandwidth.
LT4 PG.87
What is multiplexing?
Putting two or more signals into a single channel.
LT4 PG.87
What is attenuation?
Power loss.
A loss in strength as a signal travels along a transmission path.
LT4 PG.87
Optical fiber is dielectric meaning it is not affected by….
Ordinary electromagnetic fields.
LT4 PG.87
What are the advantages of fiber-optics?
Wide bandwidth Low loss Electro-magnetic immunity Light weight Small size Safety and electrical isolation
LT4 PG.87
What are some factors that the characteristics of light propagation through a fiber depend on?
Size of fiber
Composition of fiber
Light injected into the fiber
LT4 PG.88
Glass used for fibers is ultra pure, transparent silicon dioxide or fused quartz. Why would impurities purposefully be added?
To achieve desired index of refraction.
LT4 PG.88
What is Plastic-clad silica?
PCS fiber is a compromise between glass and plastic fibers by using a high quality glass core and an inexpensive plastic cladding.
LT4 PG.88
Which fiber is the least expensive and works best in a range of visible light?
Plastic Fibers.
LT4 PG.88
Optical fiber size is made up of 2 numbers, what would 50/125 tell you?
Core is first, 50 micrometers
Cladding is second, 125 micrometer diameter
LT4 PG.88
A micrometer is sometimes referred to as?
Micron
LT4 PG.89
What are the 4 most common size of optical fibers?
8 / 125
50 / 125
62.5 / 125
100 / 140
LT4 PG.89
What are the fundamental parts fiber-optic cable?
Outer Jacket Strength members Buffer Primary coating Cladding Core
LT4 PG.89 Fig 6.
What are the two types of buffer that may be used?
Loose buffer
Tight buffer
LT4 PG.89
Construction of loose buffer
Fiber is contained inside hard plastic tube
One or more fibers may be within the same tube
Tube is often filled with gel
LT4 PG.90
construction of tight buffer
Plastic jacket is bonded directly to the fiber
LT4 PG.90
What does the gel within the loose buffer do?
Keeps moisture out
Cushions glass fibers against mechanical forces
Fiber is less effected by the expanding and contracting of the cable during severe temperature changes
LT4 PG.90
Where is a tight buffer limited to in its use, and why?
Generally limited to indoor use.
During temperature variation, the plastic and the fibers expand and contract at different rates. this can result in microbends.
LT4 PG.90
Materials added to the cable to increase tensile strength are called?
Strength members.
LT4 PG.91
Common strength members are?
Kevlar
Steel
Fiberglass
LT4 PG.91
Strength members may also serve as what?
load bearing members for optical cable.
LT4 PG.91
What does the jacket do?
Provides protection to the cable against: abrasion acids oil water
LT4 PG.91
What are common jacket materials?
PVC
Polypropylene
Nylon
Teflon
LT4 PG.91
These cables contain no metal and no other electrical conductive members.
Nonconductive cables.
LT4 PG.91
These cables contain non current carrying conductive parts
Conductive cables
LT4 PG.91
These cables contain both optical fiber cables and current carrying electrical conductors.
Hybrid cables
LT4 PG.91
Common applications for outdoor cables include
Overhead cables
Direct burial cables
Indirect burial cables
Submarine cables
LT4 PG.93
steps for installing fiber-optic cables
1- survey run and choose best path 2- test cable before and after pulling 3- treat cable with care 4- do not exceed minimum bend radius 5- do not exceed maximum allowable tensile load 6- leave extra at beginning and end 7- document installation
LT4 PG.95-96
General rule for bending optic cable?
Do not bend tighter than:
- 20 times outer cable diameter during pull
- 10 times outer cable diameter after installation
LT4 PG.95
What is the general pull strength rating of most cables designed for outdoor use?
600 lb
LT4 PG.96
What section of the CEC deals with optical fiber installation?
Section 56
LT4 PG.96
We can group optical fiber cables in to three types, what are they?
Non-conductive
Conductive
Hybrid
Rule 56-102
LT4 PG.97
What is the purpose of a connector?
To join one fiber source, a detector, or another fiber.
LT4 PG.98
What convenience does a connector offer?
It allows repeated connection and disconnection of devices.
LT4 PG.98
What are the two basic types of splices?
Fusion
Mechanical
LT4 PG.98
Fusion splices are made by…
Positioning two properly prepared fiber ends and applying an electric arc to fuse the ends together.
LT4 PG.98
Mechanical splices are made by…
Using sleeve type connectors placed over prepared fiber ends. gels and adhesives provide continuous optical path between the two fibers.
LT4 PG.100
Which splice provides extremely low losses?
Fusion splices
LT4 PG.98
Which splice has higher losses?
Mechanical splice.
LT4 PG.100
Which type of splice is often used to make temporary fiber connections?
Mechanical splices.
LT4 PG.100
As the frequency of a waveform increases does the wavelength increase or decrease?
Decrease
Self-Test 4
What does the term attenuation mean?
A power loss that occurs as a signal travels over a distance.
Self-Test 4
What is an important safety precaution to observe when working with fiber-optic systems?
Never look directly into a light source or into the end of a fiber.
Self-Test 4
Which 2 layers cannot be separated in the fundamental layers of an optical fiber?
The core and cladding.
Self-Test 4
What are three hazards of working with optical-fiber cables?
Loose fiber - fiber can penetrate skin and eyes, transported through body by blood
Solvents and cleaners - often inflammable or noxious
Laser Operation - UV light can cause eye damage
Self-Test 4
What must be done to fiber after you glue it into a connector with epoxy?
Grind and polish it.
Self-Test 4
