1. INTRODUCTION TO NETWORK CABLING
MODULE 4
FIBER OPTIC-BASED SYSTEM
Introduction to Network Cabling Fiber Optic-Based Systems

2. Fiber optic Systems 4 1
Goal 4
At the completion of this module students will have an understanding of the operation and characteristics of optical systems including sources and detectors used in Fiber Optic systems. Students will be able to match systems in regards to sources, detectors and cabling systems. Students will calculate an optical loss budget.
Introduction to Network Cabling Fiber Optic-Based Systems

3. Fiber optic Systems 4
Objectives:
Define FiOS as a residential optical connectivity system Define the parts of all communications systems
Identify the role of the transmitter, receiver, message and medium
List some of the advantages and disadvantages of Fiber Optic systems
Identify the three main elements of an optic communications system and briefly explain the function of each Define transducer and give an example
Define encoding and decoding and give examples Define binary as it applies to encoding and decoding
Define types of data transmission to include analog and digital
Describe the following types of transmission systems and identify advantages and limitations: amplitude modulation, frequency modulation and digital
Identify sources and detectors as they apply to Fiber Optic transmission systems Identify desired characteristics of sources
Describe common sources to include: LED, VCSEL and LASER diode
Compare and contrast the different types of sources as to: application, cost and operation Identify cabling types used with various sources
Introduction to Network Cabling Fiber Optic-Based Systems

4. Objectives (Continued):
Fiber optic Systems 4
Objectives (Continued):
Identify safety procedures to be followed when working with sources Identify common detectors and their application
Define PIN diode and APD
Describe characteristics of sources and their application Match a source to the correct cable and detector Define an optical power budget and why it is important
Describe the term over head as it applies to a light budget Define dynamic range
Calculate with negative and positive dB readings and determine a dynamic range
Identify that when working with exponents and logarithmic numbers that subtracting is actually dividing
Given charts that describe attenuation values for connectors, splices and cables, calculate an optical system loss Calculate an optical light budget and determine if components will work with sufficient overhead
Define detector saturation as too much light at the detector Describe methods to prevent detector saturation
Using power meters, connectors, cables and attenuators determine optical budgets
Introduction to Network Cabling Fiber Optic-Based Systems

5. Fiber optic Systems 4
Introduction:
This module covers Fiber Optics Systems. The systems are the ones that move information from place to place. These systems are used in homes and businesses.
Fiber Optic systems, FOS for example, allow us to enjoy high definition television, home networking and voice communications.
In Fiber Optic systems, data moves by light but the systems work with electricity. In order to do this the information must be converted. The transmitter of the light used in Fiber Optic systems is called the source while the receiver of the information is called the detector or receiver. Both the source and the detectors are transducers that change electrical energy to light energy or light energy to electrical energy.
As you learned in last module, the development of optoelectronics was one of the keys in the development of Fiber Optic systems.
Introduction to Network Cabling Fiber Optic-Based Systems

6. Communications Systems
Fiber optic Systems 4
Fiber Optic Systems
Communications Systems
Fiber Optic systems are communications systems. The basics of Fiber Optic communication systems are the same as all forms of communication. They all share the same parts and they all convert a message using encoding and decoding. In the case of optical systems, the message is sent with light and the information is used as electricity.
All communication systems have four elements:
transmitter
receiver
message
medium of transmission
The transmitter sends out information.
The receiver is the destination of the information. The message is the information that is being sent.
The medium of transmission is how the message travels to its destination.
Figure 4.2.1
Introduction to Network Cabling Fiber Optic-Based Systems

7. Transducers - A device that changes energy from one form to another.
Fiber optic Systems 4
New Term
Transducers - A device that changes energy from one form to another.
Source - The light transmitter.
Detector - The light receiver.
FIOS - Fiber Optic System. An optical system that brings optical fiber to a residence.
Figure 4.1.1
Introduction to Network Cabling Fiber Optic-Based Systems
Figure 4.1.2

8. Transmitter - sends out information.
Fiber optic Systems 4
New Term
Transmitter - sends out information.
receiver - the destination of the information.
message - the information that is being sent.
medium - how the message travels to its destination.
Introduction to Network Cabling Fiber Optic-Based Systems

9. An optical system has these three parts:
Fiber optic Systems 4
Optical Systems
A medium can be sound, light, wires, radio signals or even Fiber Optic cable.
An optical system has these three parts:
transmitter or source, medium (optical cable and connectors) and receiver or detector
Figure 4.3.1
Introduction to Network Cabling Fiber Optic-Based Systems

10. Advantages and Disadvantages of Fiber Optic Systems advantages:4
Advantages and Disadvantages of Fiber Optic Systems
advantages:
Greater bandwidth: bandwidth is related to the amount of information that can be carried in a given length of time. Thousands of voice channels can now be sent over a single fiber strand, and with multiplexing, several channels can be sent over a single fiber.
Less loss: an optical signal can travel much further, without distortion or loss of power. Repeaters need to be placed only 50 to 70 miles apart.
Noise immunity: Fiber Optic cables are not affected by electromagnetic interference or electrostatic interference. The optical signal is unaffected by crosstalk (signals from neighboring cables) or signals generated by machinery in the vicinity of the fiber cable.
Less weight and volume: Fiber Optic cables are much smaller and lighter than copper cables. For example, a 3-inch diameter telephone cable consisting of 900 twisted-pair wires can be replaced with a single fiber strand approximately the size of a human hair.
More security: since light does not radiate from a Fiber Optic cable, it is nearly impossible to tap into the cable without detection.
More flexibility: the surface of a glass fiber is much more refined than ordinary glass. This, coupled with its small diameter, allows it to be flexible enough to wrap around a pencil.
Better economics: the cost of fiber is comparable to copper. Since transmission losses are considerably less, expensive repeaters can be spaced further apart making the overall system cost less.
More reliability: once installed, the life span of fiber is longer than copper due to its resistance to environmental corrosives such as extreme temperatures and moisture.
Introduction to Network Cabling Fiber Optic-Based Systems

11. Advantages and Disadvantages of Fiber Optic Systems Cont. 4
Advantages and Disadvantages of Fiber Optic Systems Cont.
Disadvantages of fiber systems:
Interfacing expensive: Fiber Optic transmitters, receivers, couplers and connectors are more expensive than their copper counterparts. Also, test and repair equipment is more costly.
Remote power not available: sometimes it is necessary to provide electrical power to a remote device along with the signal. This cannot be done with fiber because fiber does not conduct electricity.
Introduction to Network Cabling Fiber Optic-Based Systems

12. that can be understood by a receiver.
Fiber optic Systems 1
Encoding and Decoding
In order to send a message over distances, the message must be changed so it can be transmitted through a medium. Once received the message must be changed again so we can understand it. This process is called encoding and decoding.
New Term
Encode - the process of changing a message for transmission. Decode - the process of changing a message into a format
that can be understood by a receiver.
Introduction to Network Cabling Fiber Optic-Based Systems

13. 4 Transmitter Receiver electrical to optical optical to electrical
Fiber optic Systems 4
Transmitter
Receiver
electrical to optical
optical to electrical
User Inputs
User outputs s
Data
Voice
Video
encoder/modulator
Decode/Demodulate
light Source
light Detector
LED, 850nm, 1300nm
PIN Diode
laser, 1310nm, 1550nm
APD
Figure 4.5.1
Introduction to Network Cabling Fiber Optic-Based Systems

14. Encoding and Decoding Methods
Fiber optic Systems 4
Encoding and Decoding Methods
The two ways that information is encoded is either digital or analog.
Digital signal Analog signal 1
seconds
time in
Figure 4.6.1
A digital signal is more like a translation of the data; an analog signal is more like a description of the data.
Digital data is the 1’s and 0’s used to move information, the digital information is also called binary. Digital is the preferred method for data networks.
Fiber Optic cables also carry analog signals— video signals can be analog signals. Analog is a transmission method using continuous electrical signals that get varied in amplitude or frequency in response to similar changes in the message. The analog signal is not binary— there is a wide range of modulations it can go through.
New Term
Digital - Binary computer information that is either on or off that represent one’s and zero’s.
analog - A signal that changes in amplitude or frequency.
Introduction to Network Cabling Fiber Optic-Based Systems

15. 4 Analog Encoding and Decoding
Fiber optic Systems 4
Analog Encoding and Decoding
Analog Fiber Optic transmission systems are both am and Fm versions. In both types of systems, the optical transmitter takes in an analog, baseband video, audio or data signal and converts it to an optical signal. This optical signal varies in the intensity or the timing of the light.
Figure 4.7.1
In an AM (Amplitude Modulation) system, the optical signal is generated as a beam of light that varies in intensity in line with the original, incoming, electrical analog signal. All types of sources can be used for analog transmission. Unfortunately, sources are nonlinear devices. This means that it is difficult to control the exact brightness of the light output. Sources are designed to be either completely off or completely on and it is difficult to exactly control variations in intensity.
FM modulated signals vary the timing of the lights. In these systems, the signal is conveyed by pulsing the source completely on and off, with the speed and duration of pulsing varying in line with the original incoming signal.
Introduction to Network Cabling Fiber Optic-Based Systems

16. Fiber optic Systems 4
Figure 4.7.2
FM modulation does not have the problems that AM modulation has because the sources are either completely on or off. The timing of the lights is how the signal is encoded.
FM encoding systems also may have problems and the most common one is called crosstalk. Crosstalk is a form of signal distortion. This distortion happens when two or more FM encoded signals interfere with each other. Often in FM encoded systems more than one signal is sent over a Fiber Optic cable. Crosstalk happens within either the transmitter or receiver, encoder or decoder unit and is the result of a drift in alignment of those units.
New Term
am - Amplitude Modulation is when a signal varies in intensity.
Fm - Frequency Modulation is when a signal varies in
frequency.
Introduction to Network Cabling Fiber Optic-Based Systems

17. Digital Encoding and Decoding
Fiber optic Systems 4
Digital Encoding and Decoding
Figure 4.8.1
Unlike in AM and FM systems, pure digital transmission guarantees that the fidelity of the baseband video, audio and data signals remain constant. Data is consistent even if transmitting multiple signals through the fiber at the same time.
Introduction to Network Cabling Fiber Optic-Based Systems

18. Digital Encoding and Decoding Cont.
Fiber optic Systems 4
Digital Encoding and Decoding Cont.
In a pure digital system, the incoming baseband signals are immediately run through “analog to digital” converters within the transmitter. This converts the incoming signal or signals to a series of 1’s and 0’s, called a “digital stream.” Digital data is called binary because it only has two states; on or off.
This combined stream is used to turn on and off the emitting diode at a very high speed, corresponding to the 1’s and 0’s to be transmitted. At the receiving end, the process performed by the transmitter is reversed. The received signal is then run through a digital to analog converter, and the receiver outputs video, audio and data in the same, analog format in which the signals originated.
New Term
Binary - Computer language that uses one’s and zero’s.
Introduction to Network Cabling Fiber Optic-Based Systems

19. Activity 4.1 Communicating with Light
Fiber optic Systems 4
Activity 4.1 Communicating with Light
Use the SPOTS and the TABS to send a light transmission message.
Watch the demonstration video.
Show the movie or conduct demonstration to show the encoding and decoding of light messages
Introduction to Network Cabling Fiber Optic-Based Systems

20. Activity 4.2 Optical Systems
Fiber optic Systems 4
Activity 4.2 Optical Systems
1. A transducer changes energy from one form to another. An example of a transducer would be a hair dryer.
a. true
b. false
2. Give an example of a transducer.
_______________________________Anysuitableanswer
3. The four parts of a communications system are:
Sender
medium
receiver
message
4. Advanced optical communications systems use ___________.
a. AM
b. FM
c. Digital
d. JM
5. Describe the parts of an optical system. Any suitable answer 
Introduction to Network Cabling Fiber Optic-Based Systems

21. Fiber optic Systems 4
Sources and Detectors
In the last module we explored how light propagates in glass. In this module we will cover the devices that transmit and receive the light information.
To use Fiber Optic cables for communications, electrical signals must be converted to light, transmitted, received and converted back from light to electrical signals. This requires optical sources and detectors that can operate at the data rates of the communications system.
Figure
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

22. Fiber optic Systems 4
Sources
In a Fiber Optic system it is the source that emits light into a fiber. It is the transducer that creates light from an electrical input.
Sources have the following operating characteristics:
1. controllable output
2. small size that is capable of matching its output to the diameter of a fiber
3. ability to operate with low-level input signals
4. ability to emit bright light at specific wavelengths
5. compatibility with low-loss fibers and available detectors
6. long useable lifetime and reliability
7. he ability to quickly turn on and off creating a clean, sharply shaped pulse of light
Figure
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

23. (B) Gigabit Ethernet Short wavelength
Fiber optic Systems 4
Types of Sources
There are three main types of sources used in optical systems and they are:
Core 62.5 μm
LED
Spot Size 100 μm
light emitting Diode
(a) FDDI overfilled-launch
VCSel
Core 62.5 μm
Spot Size 35 μm
Vertical Cavity Surface emitting laser (VCSel)
(B) Gigabit Ethernet Short wavelength
Core 62.5 μm
Laser
Figure
Spot Size 10 μm
Single-mode laser
(C) Gigabit Ethernet long wavelength
Introduction to Network Cabling Fiber Optic-Based Systems

24. 4 Types of Sources Cont. New Term
Fiber optic Systems 4
Types of Sources Cont.
The type of source selected depends on the application and type of fiber. As shown above an LED will overfill a multimode cable while a VSCSel will under fill it. A laser diode is even more focused and it under fills a multimode cable even more.
New Term
FDDI - Fiber Optics Distributed Data Interface.
LED - Light Emitting Diode.
VCSel - Vertical Cavity Surface Emitting LASER.
Laser diode - Light Amplification by Stimulated Emission of Radiation diode.
Introduction to Network Cabling Fiber Optic-Based Systems

25. wide angle of dispersion (non-coherent light)
Fiber optic Systems 4
The LED
LED sources are sturdy, reliable and cheaper than LASER sources. However, the light from an LED is scattered. LED light sources are primarily used in short-distance multimode fiber systems such as computer networks within a building or building-to-building links within a campus.
wide angle of dispersion (non-coherent light)
Figure
When a voltage is applied across a Light Emitting Diode photons are produced at the semi-conductor/whisker junction. These photons leave the junction at a very wide pattern. Even though an LED looks like a light bulb it is not a light bulb. Unlike a light bulb, where most of the energy created is in the form of heat, an LED generates light and very little heat.
Figure
Introduction to Network Cabling Fiber Optic-Based Systems
Figure

26. 4 LASER Diodes Narrow angle of dispersion (coherent light)
Fiber optic Systems 4
LASER Diodes
Narrow angle of dispersion (coherent light)
Figure
LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Unlike LEDs, LASERs produce a focused coherent beam of light that does not spread out nearly as much over distance. It is for this reason that LASERs are the source of choice for long distance single mode fiber systems. LASER diodes are used for high data rate applications such as cable television trunk lines and long distance telephony. LASERs are more expensive than LEDs and the circuitry they use is much more complex. They require higher drive currents to activate and therefore generate more heat. LASERs are also more temperature sensitive and often will need coolers to sustain their operation.
LASERs have the following qualities:
-LASER light is monochromatic. (Meaning that light emitted from a LASER is of a specific wavelength.)
-LASER light is coherent. The waves are all in phase and the light is said to be collimated meaning it does not spread out over distance as much as non-LASER light.
-operate at 1310nm and 1550nm wavelengths.
-LASERs are primarily used with single mode Fiber Optic cable.
Introduction to Network Cabling Fiber Optic-Based Systems

27. Fiber optic Systems 4
LASER Diodes Cont.
The ability to focus a narrow beam is very useful. Focused LASER beams are the basis of many of the devices that we use today such as: CD players, DVD devices, and CDROM recorders and players.
Figure
New Term
Collimated - Combined light
Introduction to Network Cabling Fiber Optic-Based Systems

28. Fiber optic Systems 4
VCSEL
A vertical cavity surface emitting LASER (VCSEL) is a specialized LASER diode that promises to revolutionize Fiber Optic communications. VCSELs are more efficient and can turn on and off very quickly. The acronym VCSEL is pronounced vixel.
The VCSEL emits its coherent energy perpendicular to the boundaries between the layers. The vertical in VCSEL arises from the fact that LASER diodes are typically diagrammed showing the boundaries as horizontal planes, so the output of the VCSEL appears to emerge vertically in these drawings. The VCSEL has several advantages over edge-emitting diodes. The VCSEL is cheaper to manufacture in quantity, is easier to test, and is more efficient. In addition, the VCSEL requires less electrical current to produce a given coherent energy output.
The VCSEL emits a narrow, more nearly circular beam than traditional edge emitters; this makes it easier to get the energy from the device into an optical fiber.
Figure
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

29. 4 Source Comparison LASER Spectral width VCSEL LED Power
Fiber optic Systems 4
Source Comparison
LASER Spectral width
The semi-conductor material used to build the light source determines the wavelength and the spectral width of the
light emitted.
VCSEL
LED Power
LASER is usually more powerful than LED.
Introduction to Network Cabling Fiber Optic-Based Systems

30. Mean Time Between Failure
Fiber optic Systems 4
Source Comparison Cont.
attribute
LED
VCSel
Laser
Cost
Low
Medium
High
Mean Time Between Failure
Pulse Width
Wide
Narrower
Narrowest
Range
Short
Long
Longest
Power Requirements
Meduim
As the table points out, the LASER is much more expensive but it is also more reliable. The LASER is more focused than a VCSEL and much more focused than the LED. Think of the LED as a cheaper, short distance alternative and the LASER as the long distance source of choice.
Introduction to Network Cabling Fiber Optic-Based Systems

31. Types of Sources and Cables
Fiber optic Systems 4
Types of Sources and Cables
LED
LEDs are used in buildings, in between buildings, homes and industry.
VCSel
The OM Series of optical cables work with VCSELs for high rate data systems over LASER optimized multi-mode cable.
laser Diode
Typically LASERs are used in long range 62 mile systems.
Figure
New Term
OM - (Optical Mean) Optical Cable Enhanced multi-mode fiber designed for use with LASERs.
Introduction to Network Cabling Fiber Optic-Based Systems

32. 4 Sources Laser Diode Single Mode cable
Fiber optic Systems 4
Sources
Laser Diode Single Mode cable
LASERs are expensive so are the support systems for them. Typically LASERs are used in long range 62 mile systems. The source frequencies of light are 1310nm and 1550nm.
Figure
LED Multimode cable
LEDs are used in buildings, in between buildings, homes and industry. LEDs are matched with either 62.5μm or 50μm multimode cables. The source frequency of light is 850nm.
Figure
VCSel Multimode cable
LASER optimized systems using 50μm multimode cable. The OM Series of optical cables works with VCSELs for high rate data systems over LASER optimized multi-mode cable. The source frequency of light is 850nm.
Introduction to Network Cabling Fiber Optic-Based Systems
Figure

33. Fiber optic Systems 4
Sources Cont.
The diagram below shows a comparison of two types of Fiber Optic sources.
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

34. Important Safety Considerations in Dealing with Fiber Optic Sources
Fiber optic Systems 4
Important Safety Considerations in Dealing with Fiber Optic Sources
The source on the other end of that Fiber Optic cable could very well be a high-intensity LASER. The light that comes from it is most likely not visible. Even though you can not see the light it may be strong enough to damage your eyes permanently. So don’t look at it!
The light sources we are using in the class are not of such a high intensity, but not looking directly at the source is still a good habit to get into.
Figure
Introduction to Network Cabling Fiber Optic-Based Systems
Figure

35. Fiber optic Systems 44
Activity 4.3 Sources
Objective: Compare the primary sources used in Fiber Optic systems.1.In a Fiber Optic system, the source is the device that Sends the light signal.
Which of the following is not a characteristic of a source used in Fiber Optics?
The ability to turn on and off quickly.
The ability to emit bright light at specific wavelengths.
The ability to detect light at specific wavelengths.
The ability to match the small diameter of a fiber.
The two primary sources used in Fiber Optic systems are:
the LED and the PIN diode.
the LED and the LASER.
the LASER and the PIN diode.
the PIN diode and the photodiode.
Indicate LED or Laser for the following source characteristics.
Laser narrow light emission pattern
LED wide light emission pattern
Laser more expensive
__________Laser transmits light over longer distances
__________LED operates at 850μm or 1300μm
__________Laser operates at 1310μm or 1500μm
An analog signal is one that changes in amplitude and wavelength while a binary signal is simply on or off pulses of energy.
true
false
Introduction to Network Cabling Fiber Optic-Based Systems

36. Fiber optic Systems 4
Detectors
A detector is the device at the other end of the Fiber Optic system from the light source. It converts light wave energy into electrical energy. The detector in a Fiber Optic system is a transducer that does just the opposite job of the source. A source changes an electrical signal into light, a detector changes light into an electrical signal.
Optical detectors have the following characteristics:
-are compatible and allow for efficient light coupling.
-have a high sensitivity at the operating wavelength of the optical source.
-are able to detect fast changes in a light signal and have a sufficiently short response to handle the needed data rates.
-does not add noise into the system.
-maintains stable operation in changing environmental conditions.
Figure
Introduction to Network Cabling Fiber Optic-Based Systems
Figure

37. Fiber optic Systems 4
Detectors Cont.
There are two types of detectors used in Fiber Optic systems, the PIN Photodiodes (used with LED’s) and the avalanche Photodiode (APD—used with LASERs). These detectors are readily available and can match the wavelengths of existing light sources. The basic difference between them is their degree of conductivity when activated by a similar light source.
NEW TERM
PIN Photodiodes - Positive Intrinsic Negative (PIN) Diode. avalanche Photodiodes - APD—used with LASERs
Introduction to Network Cabling Fiber Optic-Based Systems

38. Fiber optic Systems 4
The PIN Diode
PIN diode photo detectors are commonly paired with LED sources.
Good points:
They do not require a high-voltage power supply.
They are not sensitive to temperature changes.
They are relatively inexpensive.
Bad points:
The output signal produced by the PIN diode is low, and amplifiers are usually needed to produce a sufficiently large output voltage.
Using the amplifiers introduces additional noise into the system.
In terms of signal-to-noise ratio and gain, the performance of the PIN diode is less satisfactory than that of the APD.
Figure
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

39. APD diode photo detectors are commonly paired with LASER sources.
Fiber optic Systems 4
The APD
Figure
APD diode photo detectors are commonly paired with LASER sources.
Good points:
They do not require amplification and provides its own gain.
They perform better in terms of signal-to-noise ratio and gain than the PIN diode. They are more reliable than PIN diodes.
Bad points:
They require a high voltage power supply (generates heat).
They are more sensitive to temperature change (requires cooling). They are more expensive.
Introduction to Network Cabling Fiber Optic-Based Systems

40. 4 Systems LED light sources are used for the multimode Fiber.
Fiber optic Systems 4
Systems
LED light sources are used for the multimode Fiber.
62.5μm MMF
Designed for LED systems
50 μm MMF
Can support 10Mbs to 1Gb
Can support 10Gb for limited range
LASER optimized 50μm mmf (OM-30)
Can support 10Gb for longer distances
Figure
Figure
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

41. 4-26 Multimode Cabling Systems 50μm
Fiber optic Systems 4
4-26 Multimode Cabling Systems
50μm
Two multimode core diameters are 62.5μm and 50μm. Both are recognized by standard. Both types of these optical cables are used and they can be found everywhere.
Cables with a 50μm core diameter:
have a smaller aperture.
works with a light that is more focused – less higher order modes.
has less distortion than 62.5μm cables.
have been used for a long time in the military, in Japan and in Germany.
when used with LASERs can support gigabit Ethernets.
are cheaper then single mode cable.
use the same connectors as 62.5μm.
use the same process for installation and precautions as 62.5μm.
can be used in the same system as 62.5μm.
Note: there is a one time loss calculation if systems are mixed
In the case of OM series cables the 50μm cable is optimized for 850nm
VCSELs. OM systems can support gigabit Ethernet systems for
up to 600 meters.
Figure
62.5μm
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

42. Fiber optic Systems 4
Activity 4.4 Systems
Objective: Match an optic detector and source with their recommended type of Fiber Optic cable.
1. Fill in the blanks in the diagrams below to correctly depict the systems.
Figure
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

43. 5. Match the wavelength with the most applicable optical source.
Fiber optic Systems 4
Activity 4.4 Systems
Objective: Match an optic detector and source with their recommended type of Fiber Optic cable.
2. The two most commonly used detectors in Fiber Optic systems are
a.PINdiodes
b. APD’s
3. Which optical detector requires the most amplification? APD
4. Which optical detector is typically used with a LASER?APD
5. Match the wavelength with the most applicable optical source.
a. LED
b. LASER
850 nanometers A
1310 nanometers DB
Introduction to Network Cabling Fiber Optic-Based Systems

44. 4-28 Optical Power Budgets
Fiber optic Systems 4
4-28 Optical Power Budgets
An optical power budget shows how well a system operates. Just like any other budget, an optical power budget deals with quantity, how much is needed and how much is extra. In a household budget a person has to determine how much money they have, how much money is needed for bills and expenses and how much is extra. In an optical budget we determine how much light is available, how much is needed to pass through the cable and connectors and how much extra light is not needed at this time. This extra light is called the overhead. The overhead is the extra light that may be needed in the future in case a system has to be spliced and to make up for sources and detectors that weaken over time.
When looking at an optical budget, the light lost in all of the connectors, splices and cables is calculated. The losses are subtracted from the overhead.
Figure
Figure
New Term
overhead - The extra light in a optical light budget.
Introduction to Network Cabling Fiber Optic-Based Systems

45. The range of a +10dB to -10dB provides for a dynamic range of 20dB
Fiber optic Systems 4
4-29 Dynamic Range
The dynamic range of an optical system is the amount of the light from the source plus the sensitivity of the detector. Dynamic range is determined using dBm but stated using dB.
Remember from earlier modules that the “m” in dBm refers to milliwatt. A milliwatt is a measurement of electrical power used in testing. Values less than a milliwatt are negative while values greater than a milliwatt are positive numbers. 0dBm is the same as saying one milliwatt. A milliwatt is 1/1000 of a watt.
The diagram above shows how a dynamic range works. The source has a power output of +10dBm, meaning that the light output is 10dB greater than one milliwatt.
The right side of the diagram shows the detector. This detector has a sensitivity of
-10dB. That means that a one milliwatt signal can be attenuated 10dB and still be detected.
The range of a +10dB to -10dB provides for a dynamic range of 20dB
Figure
Figure
New Term
Dynamic range - The description of the limits of operation.
Introduction to Network Cabling Fiber Optic-Based Systems

46. 4-30 Calculating Dynamic Range
Fiber optic Systems 4
4-30 Calculating Dynamic Range
Mathematical things to remember:
Dynamic range is calculated by adding a positive number and a negative number. Most technicians will change (invert) one number to make calculations easier.
If the source output is +10 and detector sensitivity is -10, a technician would calculate the dynamic range by changing the +10 to a -10 and adding the two values together. This would result in a dynamic range of -20.
= -20
Tips
Add negative numbers the same way you add positive numbers. Either number can be inverted. This method has evolved because a negative number for dynamic range is easier to work with in later calculations, or when designing testers.
Calculating dBm and dB
When calculating a dynamic range you are not really adding or subtracting dBm. Remember that a dB and a dBm are non-liner numbers that are expressed as logs and exponents. When non-liner numbers are added together they are really multiplied. Once multiplied the milliwatt factor is cancelled out resulting in dB.
-10dBm + -10dBm = - 20dB
Technicians are not concerned about the mathematics, they just quickly calculate by adding and dropping the milliwatt constant.
Introduction to Network Cabling Fiber Optic-Based Systems
Figure

47. 4-31 Calculating System Losses
Fiber optic Systems 4
4-31 Calculating System Losses
Signal loss is the amount of attenuation of all of the cables, connectors and splices.
loss = connector attenuation + cable attenuation + splice attenuation
Connectors
According to standard the maximum attenuation of a mated pair of connectors should not exceed 0.75dB.
Splices
According to standard the maximum attenuation of a splice should not exceed 0.3dB.
Cable
Standard maintains that cable should not exceed 3.5dB per kilometer. Cable attenuations do vary with the type of cable. Refer to the Fiber Optic card or manufacturer’s specs for attenuations.
To calculate the optical fiber losses, one must consider all possible sources of attenuation and add them together.
Introduction to Network Cabling Fiber Optic-Based Systems

48. Activity 4.5 Determine Optical Loss
Fiber optic Systems 4
Activity 4.5 Determine Optical Loss
2.25 1.
Three mated pairs of connector’s
__________ dB
0.3
One Splice
1 km of 850nm 62.5 optical cable
3.5 dB
Total
6.05
1.5 2.
Two mated pairs of connector’s
Two splices
0.6
1 km of 1300nm 62.5um
3.6 3.
Four mated pairs of connector’s
3.0
One half km of single mode cable
0.5
Objective: Calculate attenuations
Use the Fiber Optic Card and calculate the following losses
Introduction to Network Cabling Fiber Optic-Based Systems

49. 4-33 Optical Budget For example: Dynamic range 20dB loss 16dB overhead
Fiber optic Systems 4
4-33 Optical Budget
An optical budget is calculated by subtracting the system loss from the dynamic range.
An optical power budget gives the technician and the owner of the equipment an idea on how well the system should work. It also provides for future splices or additional connectors and equipment aging.
For example:
Dynamic range
20dB
loss
16dB
overhead
4dB
Figure
Introduction to Network Cabling Fiber Optic-Based Systems

50. Activity 4.6 Calculating a Loss Budget
Fiber optic Systems 4
Activity 4.6 Calculating a Loss Budget
Objective: To correctly calculate a Fiber Optic loss budget.
Calculate the Fiber Optic loss budget for the given situation described. 1.
Calculate the total system attenuation (use the color code card)
Two km of optical cable (850nm) 7 dB
3.75
Five mated connector pairs
0.6
Two splices
11.35
Total system attenuation 2.
Calculate the dynamic range
Source output
12dBm
Detector sensitivity
-8dBm
Dynamic range 20
Using the calculations above determine the link margin.
Link margin (attenuation subtracted from dynamic range) _________8.65dB
Will the system be within approved parameters? yes
4. Repeat the calculations for question three using 4km of cable. Link margin 1.65 dB
Introduction to Network Cabling Fiber Optic-Based Systems

51. 4-35 Saturation Levels 4 New Term
Fiber optic Systems 4
4-35 Saturation Levels
Too much light can be disrupting to an optical system. Just like too little light, too much light can be a problem. Systems that are designed for long range, do not necessarily work for short runs of cable inside a building. Too much light into a detector can overwhelm it. Similar to spots you may see after a flash. When a detector is overwhelmed with too much light, it is called saturated. When a detector is saturated it is not working correctly.
To insure that the optic system does not saturate do not exceed the safe operating limit. That limit is stated on the detector spec sheets or can be found on-line.
a typical APD
Safe limit of 2dBm
Sensitivity of -28dBm
New Term
Figure
Figure
Saturated - too much light causes a detector not to work properly.
Introduction to Network Cabling Fiber Optic-Based Systems

52. Activity 4.7 Determining a Systems loss
Fiber optic Systems 4
Activity 4.7 Determining a Systems loss
Using cables, connectors and optic attenuators, determine the
attenuation of a system.
Using cables, connectors, power meters and light sources determine a systems loss. Add attenuators as necessary in this activity. Students can list responses on activity sheet.
Introduction to Network Cabling Fiber Optic-Based Systems

53. Module Review 4 Here’s what we have covered in this module:
Fiber optic Systems 4
Module Review
Here’s what we have covered in this module:
The two main light sources for Fiber Optic systems are LEDs (Light Emitting Diodes) and LASERs (Light Amplification by Stimulated Emission of Radiation).
Optic fibers can carry digital or analog signals.
LEDs produce low intensity, non-coherent light that is subject to dispersion when transmitted over distance. They are usually used with multimode fiber.
LASERs produce high intensity coherent light that is much less susceptible to dispersion. LASERs are normally used with single-mode fiber.
LEDS are cheaper and not sensitive to heat, cold or dampness. They are also not as powerful, and emit their light in a wide angle.
LASERs are more powerful and more reliable. They are also more sensitive to heat, cold or dampness and cost more.
The detector for an LED system is usually a Positive Intrinsic Negative (PIN) diode. The detector for LASER systems is normally the Avalanche Photo Diode (APD).
PIN diodes are less powerful than APDs and frequently need amplification. This can lead to additional noise in the system.
APDs do not need amplification, but are more temperature-sensitive and may require cooling.
Fiber Optic systems have many advantages over copper-based systems, including economy, greater bandwidth, less signal loss, less weight, more flexibility and greater reliability.
Fiber Optic systems also have disadvantages. Chief among them are that interface equipment is more expensive and that fiber cannot conduct electricity to power devices that might be used.
Introduction to Network Cabling Fiber Optic-Based Systems

54. New Terms 4 Term Definition
Fiber optic Systems 4
New Terms
Term Definition
am Amplitude Modulation is when a signal varies in intensity.
analog A signal that changes in amplitude or frequency.
APD Avalanche Photo Diode. A detector normally used with LASER light
sources.
Binary A code based on two conditions: on/off, yes/no, light/dark.
Collimated- Combined light.
Decode The process of changing a message into a format that can be
understood by a receiver.
Detector A transducer that changes a light signal back into electrical energy.
Digital A signal that uses numbers to represent the data.
Dynamic range-The description of the limits of operation.
encode The process of changing a message for transmission.
Fm Frequency Modulation is when a signal varies in frequency.
FIos Fiber Optic System. An optical system that brings optical fiber to a
residence.
laser Diode-Light Amplification by Stimulated Emission of Radiation. A high-
intensity light source that produces a focused coherent beam of light.
LED Light-Emitting Diode. A low-power light source for optic fiber.
message The information that is being sent.
medium How the message travels to its destination.
overhead The extra light in a optical light budget.
PIN Photodiode-Positive Intrinsic Negative Diode. A detector normally used with LED
receiver The destination of the information.
Saturated-Too much light causes a detector not to work properly.
Source A transducer that changes electrical energy into a light signal.
Transducer-A device that changes energy from one form to another.
Transmitter-Sends out information.
VCSel Vertical Cavity Surface Emitting LASER.
Introduction to Network Cabling Fiber Optic-Based Systems

55. Introduction to Networking Fiber Optic-Based Systems (Version 3.3)
© by C-Tech Associates, Inc.
TRADEMARK ACKNOWLEDGEMENTS
All Trademarks and Registered Trademarks are the property of their respective owners. Any oversight in acknowledging trademarks shall not be regarded as affecting the validity of any of these or as an infringement on them.
ISBN# Fiber Optics 3.3 Student Manual and
CD Fiber Optics 3.3 Student Manual, CD and Consumables
Fiber Optics 3.3 Instructor Manual and CD
Introduction to Network Cabling Fiber Optic-Based Systems

56. QUESTIONS? Module Test Time! 4 Fiber optic Systems
Introduction to Network Cabling Fiber Optic-Based Systems