Transcript
Optical Fiber Communication Systems Losses And Sensor Applications
CONTENTS:
1. INTRODUCTION……………………………………………………….………....4
1.1 CONNECTOR LOSSES…………………………………………….………….4
1.1.1 INTRINSIC LOSSES…………………………………………..............5
1.1.2 METHODS TO MINIMIZE INTRINSIC LOSSES……………………5
1.2 EXTRINSIC LOSSES………………………………………………………….5
1.3 METHODS TO MINIMIZE EXTRINSIC LOSSES…………………………..6
2. BENDING LOSS…………………………………………………………………..6
2.1 METHODS TO MINIMIZE BENDING LOSS………………………………..8
3. OPTICAL LOSS……………………………………………………………………8
3.1 METHODS TO MINIMIZE OPTICAL LOSS…………………………………9
4. MATERIALISTIC ABSORPTION LOSSES IN SILICA GLASS FIBERS………9
4.1 INTRINSIC ABSORPTION……………………………………………………9
4.1.1 METHODS TO MINIMIZE INTRINSIC LOSS……………………...10
4.2 EXTRINSIC ABSORPTION………………………………………………….10
4.2.1 METHODS TO MINIMIZE EXTRINSIC LOSS……………………..11
5. LOSS IN FIBER OPTIC DUE TO HYDROGEN ABSORPTION……………….11
5.1 METHODS TO MINIMZE LOSS IN FIBER OPTIC DUE TO HYDROGEN
ABSORPTION………………………………………………………………...12
6. LOSS IN FIBER OPTIC DUE TO NUCLEAR RADIATION EXPOSURE……..12
6.1 MEHTODS TO MINIMIZE LOSS IN FIBER OPTIC DUE TO NUCLEAR
RADIATION EXPOSURE…………………………………………………....13
7. JOINT LOSS AND FIBER ALIGNMENT LOSS……………………………...…13
7.1 METHODS TO MINIMIZE JOINT LOSS AND FIBER ALIGNMENT LOSS
8. CONCLUSION …………………………………………………………………...15
9. INTRODUCTION…………………………………………………………………15
9.1 MICROBEND FIBER OPTIC SENSORS…………………………………….15
10. BASIC FIBER OPTIC SENSOR SYSTEM………………………………………19
10.1 INTENSITY TYPE FIBER OPTIC SENSOR MICROBENDING………19
10.2 INTENSITY TYPE FIBER OPTIC SENSOR USING EVANESCENT
WAVE COUPLING…………………………………………………………...19
11. MEASURING TEMPERATURE SENSORS IN PROCESS CONTROL……….20
11.1 SEMICONDUCTOR ABSORPTION SENSORS………………………...20
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12. BRAGG GRATING SENSOR FOR STRAIN MEASUREMENT……………….21
13. MEASUREMENT OF PIEZORESISTIVE PRESSURE SENSOR………………22
14. PERFORMANCE OF FIBER OPTICS BASED SENSORS IN COMPARISION
WITH TRADITIONAL SENSORS……………………………………………….23
15. CONCLUSION……………………………………………………………………24
16. TRANSMITTER AND RECEIVER PERFORMANCE CHARACTERISTICS OF
LED AND LASER………………………………………………………………..24
16.1.1 TRANSMITTER PERFORMANCE CHARACTERSITICS OF LED
AND LASER………………………………………………….............24
16.1.2 RECEIVER PERFORMANCE CHARACTERSITICS OF LED AND
LASER………………………………………………………………...27
16.2 COMPARISION OF LED SYSTEM AND LASER SYSTEM………………….30
17. REFERENCES………………………………………………………………………...31
LIST OF FIGURES PAGE NO
Fig 1.1.1 Intrinsic losses…………………………………………………………….............5
Fig 3.1 Optical loss in fiber…………………………………………………………………9
Fig 9.1 (a) Microbend fiber optic system………………………………………….............16
Fig 10.1 Fiber optic sensor system using microbending…………………………………..19
Fig 10.2 Fiber optic sensor system using evanescent wave coupling……………………..20
Fig 11.1 Temperature-dependent on GaAs light absorption…………………………........14
Fig 13.1 Piezoresistive pressure sensor chip………………………………………………22
LIST OF GRAPHS PAGE NO
Fig 1.2.1 Lateral Displacement……………………………………………………………..6
Fig1.2.2 Longitudinal Displacement………………………………………………………..6
Fig 2.1 Fiber attenuation due to microbending and macrobending…………………………7
Fig 2.2 Losses v/s mode-field diameter…………………………………………………….7
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Fig 4.1 Intrinsic material absorption loss………………………………………………….10
Fig 4.2 Extrinsic material absorption loss…………………………………………………11
Fig 5 Loss v/s wavelength in treated and untreated loss…………………….…………….12
Fig 6 Nuclear Radiation Exposure losses………………………………………………….13
Fig 7.1 Insertion loss due to lateral and longitudinal misalignments………………...........14
Fig 7.2 Insertion loss due to angular misalignment………………………………………..14
Fig 9.1 (b) Parabolic-profile fiber…………………………………………………………17
Fig 9.1 (c) Step-profile fiber………………………………………………………………18
Fig 12. Transmission spectrum of grating v/s wavelength……………………………… 21
Fig 13.2 Voltage v/s Pressure……………………………………………………………...23
APPENDICES : LIST OF TABLES:
Table 1- Operating Condition for LED Transmitter……………………………………....25
Table 2- Operating Condition for LASER Transmitter……………………………………25
Table 3- Electrical Characteristics of LED Transmitter…………………………………...25
Table 4- Electrical Characteristics of LASER Transmitter………………………………..26
Table 5- Optical Characteristics of LASER Transmitter………………………………….26
Table 6- Operating Conditions of LED Receiver …………………………………………27
Table 7- Operating Conditions of LASER Receiver………………………………………27
Table 8- Electrical Characteristics of LED Receiver……………………………………...28
Table 9- Electrical Characteristics of LASER Receiver…………………………………..28
Table 10- Optical Characteristics of LED Receiver……………………………………….28
Table 11- Optical Characteristics of LASER Receiver……………………………………29
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FIBER OPTIC LOSSES
1. INTRODUCTION
There are various numbers of reasons for the losses in optical fibers. These losses may
occur due to different types of material components being used in transmitting signals
over the transmission path. It can be categorized into numerous areas like Connector
losses which consists of intrinsic and extrinsic, Bending losses which consists of micro
bending and macro bending and Optical loss in which power plays major role. Hence
all kinds of losses are explained in detail below.
1.1 CONNECTOR LOSS:
This is one of the types of fiber optic losses; there are different factors which
results in attenuation of any two given fibers connected together. Connector losses
are divided into two, mainly intrinsic losses which are caused by the fiber. And the
next extrinsic losses caused by the connectors. Splices and Connectors when
inserted in given line direction are termed as insertion loss. Here we need to
considered short length of the fiber because if higher mode is taken then there is
higher numerical aperture and large size of the spot which causes higher losses at
times. So length plays am important factor in case of connector losses.
1.1.1 INTRINSIC LOSSES:
In general losses occurs because none of the fibers are same, there may be a
mismatch of numerical aperture, core area and core. When numerical aperture of
first fiber is larger than that of second it results in waste of light. And when light
travels in different direction, loss does not occur but gain is wrongly indicated.
For NA1>NA2, light transmitted in decibels.
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Fig 1.1.1 Intrinsic losses.
(Source: James N. Downing, 2005)
In the opposite direction losses do not occur but the final intrinsic loss can be in
three cases. Firstly if in over lapped cores the geometry result, mismatch of
cladding diameter result and the ellipticity of the cores.
1.1.2 METHODS TO MINIMIZE INTRINSIC LOSSES:
The use of core and the cladding is the most better matched results to
minimize and in fact eliminate the intrinsic losses.
1.2 EXTRINSIC LOSSES:
In this case it all depends on the connectors used, since if any misalignment occurs
while connecting the connectors there occur some changes in fiber cores. The
displacement is of two types i.e. lateral and longitudinal displacement.
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In case of the lateral displacement as shown in fig 1-2 for different displacements
ratios the graph shown is used in finding the loss. A loss of 2 db occurs for 30%
displacement. Where as in case of longitudinal displacement, if the angle is not
aligned correctly in results in producing more number of losses which in term gives
more emphasis on polishing of fiber and cleaving by using end cleaving procedure.
Fig 1.2.1 Lateral Displacement Fig1.2.2 Longitudinal Displacement
(Source: James N. Downing, 2005) (Source: James N. Downing, 2005)
1.3 METHODS TO MINIMIZE EXTRINSIC LOSSES:
There are different kinds of techniques used to eliminate the losses, whereas here in
this case the glass refining technique is used to reduce to acceptable levels.
2. BENDING LOSS:
There are two types of bending losses namely, microbending loss and
macrobending loss. These two losses are expressed in single mode fibers at 1550
nm region, the wavelength of lower cut off gets affected more precisely than other.
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Fig 2.1 Fiber attenuation due to microbending and macrobending
(Source: V.S. Bagad, 2008)
To get low bending loss the diameter of mode field should be small, hence mode
field plays an important role in case of bending loss. The radius which is measured
inside the object is the minimum radius an object can be bend is termed as bend
radius, so if the bending radius is smaller then losses are higher and when the radius
is higher the losses are smaller. Hence bend radius is also vital in case of bending
loss.
Fig 2.2 Losses v/s mode-field diameter.
(Source: V.S. Bagad, 2008)
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2.1 METHODS TO MINIMIZE BENDING LOSSES:
1. The manufacturing of cable must be done to reduce the strain in case of
microbending loss.
2. In microbending attenuation is reduced by controlling coating of the fiber.
3. The fiber should be free from external pressure in microbending loss.
4. In case of macrobending, designing plays an important role i.e the
refractive index differences should be long.
5. And the wavelength should be as small as possible in order to reduce losses
in macrobending.
3. OPTICAL LOSS:
When a signal is transmitted along a path it mainly deals with the power, the
wavelength varies with the power. If signal power is reduced when travelling on the
path then it is termed as loss in signal. For a fiber with specific wavelength, the
ratio of output power to the input power is defined as optical loss.
Loss ratio= Tr = Pout/Pin
Loss ratio: Loss of power at a particular wavelength
Tr= Transmittance
Pout= average of output power of fiber
Pin = average of input power of fiber
In any passive path the output power of the optical fiber is always less than or equal
to the input power of the optical fiber. The fig 3.1 below shows the optical loss in
the fiber input as Input power (Pin) and output as output power (Pout).
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Fig 3.1 Optical loss in fiber.
(Source: Bob Chomycz, 2009)
3.1 METHODS TO MINIMIZE OPTICAL LOSS:
There are different reasons for the loss in optical fiber hence various methods
should be taken care of like the connectors when connected at the transmitter end
and at receiver end it should be properly connected .
4. MATERIALISTIC ABSORPTION LOSSES IN SILICA GLASS FIBERS:
In optical fibers there are number of reasons for the attenuation of the signal. The
absorption of the material is a mechanism of loss which is linked with the
combination of the process of fabrication in optical fiber and composition of the
material. So when optical power is transmitted heat is dissipated in the form of
waveguide. Hence the absorption is either in intrinsic or extrinsic.
4.1 INTRINSIC ABSORPTION:
A glass of Silica which is pure has very less intrinsic absorption. There are not
only one absorption in this but there are two intrinsic absorption.The graph
deals with the losses and Ultraviolet absorption and Infrared absorption with the
photon energy. The attenuation of the intrinsic loss mechanisms is pure in
GeO2-SiO2. It shows that absorption is more in Ultraviolet region than in
infrared region.
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Fig 4.1 Intrinsic material absorption loss
(Source: John M. Senior, 1992)
4.1.1 METHODS TO MINIMIZE INTRINSIC ABSORPTION LOSS:
The use of core and the cladding is the most better matched results to
minimize and in fact eliminate the intrinsic losses.
4.2 EXTRINSIC ABSORPTION:
From the impurities of transition metal element a large amount of signal
attenuation is linked with the extrinsic absorption. The absorption losses are
mainly due to peak wavelength and different metallic ion impurities in glasses.
The impurities like chromium and copper can cause attenuation excess of 1 dB
km-1. Hence other absorption loss is due to water which is dissolved in glass.
The figure below shows the absorption spectrum for the hydroxyl.
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Fig 4.2 Extrinsic material absorption loss
(Source: John M. Senior, 1992)
4.2.1 METHODS TO MINIMZE EXTRINSIC ABSORPTION LOSS:
There are different kinds of techniques used to eliminate the losses, whereas here in
this case the glass refining technique is used to reduce to acceptable levels.
5. LOSS IN FIBER OPTIC DUE TO HYDROGEN ABSORPTION:
The characteristic of spectral attenuation is affected due to the diffusion of the
hydrogen in optical fiber. New absorption peaks are formed by altering the spectral
loss, which causes in increase of hydrogen absorption in optical fiber.
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Fig 5 Loss v/s wavelength in treated and untreated loss.
(Source: John M. Senior, 1992)
5.1 METHODS TO MINIMZE HYDROGEN ABSORPTION LOSS:
1. Cable should be given special care since if dipped or inserted in water it may cause
losses and selection of cable plays an important factor since each cable has its own
specification.
2. Hence the cable needs to be pressurized to prevent water from entering into it.
3. The fiber cable can be cleansed using inert gas.
6. LOSS IN FIBER OPTIC DUE TO NUCLEAR RADIATION EXPOSURE:
The characteristics while transmission of optical fiber cables have been reduced in
quality because of nuclear radiation. At the center of the fiber core the radiation
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makes colour and it results in spectral attenuation. The graph below shows the
effects of nuclear radiations with two optical fibers.
Fig 6 Nuclear Radiation Exposure losses
(Source: John M. Senior, 1992)
6.1 METHODS TO MINIMIZE NUCLEAR RADIATION LOSS:
1. With the help of photo bleaching the radiation which is induced can be
attenuated.
2. Using fibers which are resistant of radiation like silica cladding fiber
reduces gamma ray radiation.
7. JOINT LOSS AND FIBER ALIGNMENT LOSS:
When joining the optical fibers there may be misalignments being occurred which
results in different typer of alignments leading to losses. There are losses due to
lateral and longitudinal misalignments and losses due to angular misalignments.
Following are the graphs shown for the misalignments occurred.
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Fig 7.1 Insertion loss due to lateral and longitudinal misalignments
(Source: John M. Senior, 1992)
Fig 7.2 Insertion loss due to angular misalignment.
(Source: John M. Senior, 1992)
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7.3 METHODS TO MINIMIZE FIBER ALIGNMENT LOSS:
The misalignment due to lateral is reduced by keeping the lateral offset value lateral below
5% of the core diameter of the fiber which results in reducing the insertion loss at a joint
below 0.5dB.
8. CONCLUSION:
From all the above losses explained we can understand the main reason behind the
losses which are occurring in fiber optics, there are few advantages and
disadvantages in fiber optic but if these losses are overcome then it will be a good
source for transmitting and receiving data and to be termed as the best means of
communication.
FIBER OPTIC BASED SENSORS:
9. INTRODUCTION:
The signals are transmitted in the form of light in the optical fiber as well as in it can be
very useful as sensors to measure different quantities. In case of industrial sectors sensors
play vital role since it will be helpful to keep an eye on such huge environment and if any
other method is used then it is quite expensive and difficult task. Therefore the sensors are
used to measure for different quantities using fiber optics technology. All the principles of
operation of the fibre optics based sensors used to measure such quantities.
9.1 MICROBEND FIBER OPTIC SENSORS:
This is one of the initial fiber optic sensor of all the sensors being used in fiber
optics. The losses occurring in microbend fiber optic resulted in designing the new
measurement technique for different variables such as temperature and pressure.
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This sensor has many characteristics which resulted in using them in many
applications. In this case the range and sensitivity are increased for the variable
which can produce better results if increased where as sensitivity is decreased for
variables which are not needed.
Fig 9.1 (a) Microbend fiber optic system
(Source: K.T.V. Grattan and B.T. Meggitt, 1999)
There are two pressure plates in which there is an input given as laser light in the
fiber and is kept between the two plates to the detector. Since the light is not
allowed to come out in the open area the microbender is termed as intrinsic fiber
optic sensor.
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A(mm)
Fig 9.1 (b) Parabolic-profile fiber
(Source: K.T.V. Grattan and B.T. Meggitt, 1999)
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Fig 9.1 (c) Step-profile fiber
(Source: K.T.V. Grattan and B.T. Meggitt, 1999)
In the complete given length to get the best out of the fiber the performance of the
binder was studied. The jacket connected to the fiber namely Teflon jacket and
rubber jacket contained sensitivity in microbend same when compared to fiber
without the jacket.
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10. BASIC FIBER OPTIC SENSOR SYSTEM:
Depending on the particular functions of light each sensor is characterized by its
parameter. Frequency, phase and amplitude are some of the parameters. There are
different number of intensity based fiber optic sensors.
10.1 INTENSITY TYPE FIBER OPTIC SENSOR USING
MICROBENDING:
Due to bending of the fiber losses occur known as microbending losses. So the
light which is going to come at the receiving end depends on the amount of losses
occurred when the light was transmitted. Hence the microbending is measured to
use the fiber optic sensor
Fig 10.1 Fiber optic sensor using microbending.
(Source: Francis T.S. Yu and Shizhuo Yin, 2002)
10.2 INTENSITY TYPE FIBER OPTIC SENSOR USING EVANESCENT
WAVE COUPLING:
When light travels in a single mode fiber optic it not only go through the core but
also enters into the cladding region, so the wave of light in the region of cladding
is termed as evanescent wave. If two fibers are close to each other then the chances
of coupling is more. Another light travels in second fiber and a new evanescent
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wave is created such that both are quite close to each other which results in
coupling of both the waves. Hence it is known as evanescent wave coupling.
Fig 10.2 Fiber optic sensor using evanescent wave coupling.
(Source: Francis T.S. Yu and Shizhuo Yin, 2002)
11. MEASURING TEMPERATURE SENSORS IN PROCESS CONTROL:
Sensors play an important role in many electrical and chemical industries, here
temperature sensors is the most useful of all sensors. There are two types of
temperature sensors used namely low temperature sensor and high temperature
sensor. The range of low temperature sensor is -100 to +4000 C and if high
temperature sensor it is 500 to 20000 C.
11.1 SEMICONDUCTOR ABSORPTION SENSORS:
The graph below shows the curve with intensity and wavelength of GaAs
absorption curve. It is also one type of temperature sensor, the wavelength of the
signal light of the absorption edge shift is higher than the wavelength of reference
light.
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Fig 11.1 Temperature-dependent on GaAs light absorption.
(Source: Sabrie Soloman, 1999)
12. BRAGG GRATING SENSOR FOR STRAIN MEASUREMENT:
Compared to other sensors where different types of techniques are used, in this case
of Bragg grating sensor the fabrication technique is used which is quite expensive
and complex of all. The gratings needs to be fabricated at an order of 10-3. The
graph shown below transmission spectrum of grating which is long period and there
occurs spiky losses and discrete band signals.
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Fig 12. Transmission spectrum of grating v/s wavelength.
(Source: Michael Bass and Eric W. Van Stryland, 2002)
13. MEASUREMENT OF PIEZORESISTIVE PRESSURE SENSOR:
It consists of a silicon chip which results in forming of silicon at the bottom of the
diaphragm. Maximum strain occurs at the corners when there is a deflection caused
by difference in the pressures. Since the external circuit is electronic the pressure
can be sensed with the change in resistivity.
Fig 13.1 Piezoresistive pressure sensor chip
(Source: Sabrie Soloman, 1999)
Hence the graph below shows output voltage with respect to the pressure times full
scale range with different over range factors. There are three different pressure
range being taken into account.
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Fig 13.2 Voltage v/s Pressure
(Source: Sabrie Soloman, 1999)
14. PERFORMANCE OF FIBER OPTICS BASED SENSORS IN
COMPARISION WITH TRADITIONAL SENSORS
(a) Firstly fiber optic sensors are used in the areas where traditional sensors cannot
be taken use of.
(b) Fiber optic sensors have much better range and resolution than traditional
sensors.
(c) Measurement in fiber optic sensors is exact and accurate.
(d) Whether in series or in parallel, the fiber optic sensors can be multiplexed
easily.
(e) Cost is less per channel in case of fiber optic sensors.
(f) Fiber optic sensors are secure against electromagnetic interference.
(g) The operation done in fiber optic sensors is passive and it is safe when
compared to traditional sensors.
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15. CONCLUSION:
We can conclude that there are different numbers of uses of fiber optics sensors
using fiber optics technology. The quantities used in measuring fiber optics sensors
are temperature, pressure and strain by updating the fibre so that the quantity to be
measured modulates the intensity based on the losses, polarization, phase, and
wavelength or transit time. Hence fiber optic sensors are more advantageous than
traditional sensors.
16. TRANSMITTER AND RECEIVER PERFORMANCE CHARACTERISTICS
OF LED AND LASER.
Firstly the performance is divided into two types, Laser and LED transmitter
characteristics and next Laser and LED receiver characteristics.
16.1.1 TRANSMITTER PERFORMANCE CHARACTERSITICS OF LED AND
LASER
The transmitter performance is LASER and LED is done in three different
characteristics
(a) Operating Conditions
(b) Electrical Characteristics
(c) Optical Characteristics
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APPENDICES
Table 1- Operating Condition for LED:
Parameter Symbol Min Type Max Unit
Ambient:
Operating Temp
TA 0 70 oC
Supply Voltage Vcc 4.75 5.25 V
Output Load RL 50
Table 2- Operating Conditions for Laser:
Parameter Symbol Min Type Max Unit
Ambient:
Operating Temp
TA 0 -70 oC
Supply Voltage Vcc 3.1 3.5 V
Data output Load RDL 50 Ω
(a) Operating Conditions : The maximum and minimum temperatures of
both LED and LASER are kept same since they can operate without
damage. The voltage given is the operating voltage which is different
from the input voltage and output voltage. In case of LED the minimum
and maximum supply voltage is higher when compared to LASER’s
maximum and minimum supply voltage. And the data output load is
same in both operating conditions.
Table 3- Electrical Characteristics of LED:
Parameter Sym
bol
Min Type Max Unit
Supply current ICC 145 185 mA
Power Dissipation PDISS 0.76 0.97 W
I/P current- Low IIL -350 0 -1.475 µA
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I/P current-High IIH 14 350 µA
Table 4- Electrical Characteristics of Laser:
Parameter Sym
bol
Min Type Max Unit
Supply current ICC 145 185 mA
Power Dissipation PDISS 0.76 0.97 W
Data o/p Rise time tr 125 150 ps
Data o/p fall time tf 125 150 ps
(b) Electrical Characteristics : It consists of the requirements of supply
current, data input and power dissipated by the device, that is power
consumption. The maximum supply current is higher in LED when
compared to LASER’s maximum supply current. The maximum power
dissipation is lower in LASER when compared to LED’s maximum
power dissipation.
Table 5- Optical Characteristics of Laser:
Parameter Symbol Min Type Max Unit
Center wavelength λc 1260 1360 nm
Spectral width Ϭ 1.8 4 nm rms
Optical rise time tr 30 70 ps
Optical fall time tf 150 225 ps
(c) Optical Characteristics : Here drive current plays an important role, since
the output depends on it. The laser operates with an insufficient LED
when the drive current is low. The action of the lasing begins when it
crosses the threshold value.
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16.1.2 RECEIVER PERFORMANCE CHARACTERSITICS OF LED AND
LASER:
The receiver performance is LASER and LED is done in three different
characteristics.
(a) Operating Conditions
(b) Electrical Characteristics
(c) Optical Characteristics
Table 6- Operating Conditions of LED:
Parameter Symbol Min Type Max Unit
Operating Temp TA 0 70 0C
Supply voltage VCC 4.75 5.25 V
Output Load RL 50 Ω
Table 7- Operating Conditions of Laser:
Parameter Symbol Min Type Max Unit
Operating Temp TA 0 +70 0C
Supply voltage VCC 3.1 3.5 V
Data Output Load RDL 50 Ω
(a) Operating Conditions : It describes the maximum and minimum
temperature and range of the voltages by which the device can operate
without damaging. The minimum and maximum supply voltage in
LASER is lower when compared to LED’s minimum and maximum
supply voltage. And the ambient operating temperature is same for both.
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Table 8- Electrical Characteristics of LED:
Parameter Sym
bol
Min Type Max Unit
Supply current ICC 82 145 mA
Power Dissipation PDISS 0.3 0.5 W
Data o/p Rise time tr 0.35 2.2 ps
Data o/p fall time tf 0.35 2.2 ps
Table 9- Electrical Characteristics of Laser:
Parameter Sym
bol
Min Type Max Unit
Supply current ICC 115 140 mA
Power Dissipation PDISS 0.38 0.49 W
Data o/p Rise time tr 125 150 ps
Data o/p fall time tf 125 150 ps
(b) Electrical Characteristics : It deals with supply current requirements,
data output characteristics and power dissipated by the device. The
maximum supply current is slightly greater in LED performance when
compared to LASERS maximum supply current. Hence LED maximum
supply current is higher.
Table 10- Optical Characteristics of LED:
Parameter Symbol Min Type Max Unit
Optical i/p
Power maximum
PIN MAX -14 -11.8 dBm avg.
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Operating wavelength I 1270 1380 nm
Table 11- Optical Characteristics of Laser:
Parameter Symbol Min Type Max
Receiver sensitivity PIN Min -23 -19
Receiver overload PIN Max -3 +1
i/p operating wavelength Λ 1260 1570
(c) Optical Characteristics : In LED performance characteristics it includes
minimum optical input power, maximum optical input power and
operating wavelength whereas in LASER’s performance characteristics
it includes output power, wavelength, spectral width and back reflection
sensitivity. The minimum operating wavelength in LED is higher
when compared to LASER’s minimum operating wavelength. And
maximum operating wavelength in LASER is higher when compared
to LED’s operating wavelength.
16.2 COMPARISION OF LED SYSTEM AND LASER SYSTEM:
Parameter LED LASER
Data Rate
Transmission Distance
Circuit Complexity
Cost
Life cycle
Power output
Coherence
Applications
Low
Smaller
Simplex
Low
Small
Low output
Incoherent
Moderate Distance
Low data rate
High
Greater
Complex
High
Very large
High output
Coherent
Long Distance
High data rate
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Generally LED is used for smaller transmission distances so low data rates where
as LASER is used for greater transmission distances so high data rates.
17. References:
1. (James N. Downing, 2005, “Fiber-Optic Communications”, ISBN: 1-4018-
6635-2)
2. (V.S. Bagad, 2008, “Optical Communications”, ISBN: 9788184314823)
3. (Bob Chomycz, 2009, “Planning Fiber Optic Networks”, ISBN: 978-0-07-
149919-4)
4. (John M. Senior, 1992, “Optical Fiber Communcations Principles and
Practice”, ISBN: 978-0-13-032681-2)
5. (K.T.V. Grattan and B.T. Meggitt, 1999, “Optical Fiber Sensor Technlogy”,
ISBN: 0-412-82570-8)
6. (Francis T.S. Yu and Shizhuo Yin, 2002, “Fiber Optic Sensors”, ISBN: 0-8247-
0732-X)
7. (Sabrie Soloman, 1999, “Sensor Handbook”, ISBN: 978-0-07-160570-0)
8. (Michael Bass and Eric W. Van Stryland, 2002, “Fiber Optics Handbook: fiber,
devices and systems for optical communication”, ISBN: 0-07-138623-8)
OPTICAL FIBER COMMUNICATION SYSTEMSPage 30
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