This post gives you complete information regarding practical implementation of Microwave and Optical Communications. The requirements, procedure to do the experiments, and the results are kept in the manual below.
To download the lab manual click on "CLICK ME": CLICK ME
List of experiments that are performed are listed below with requirements:
Part – A :
1. Reflex Klystron Characteristics.
2. Gunn Diode Characteristics.
3. Directional Coupler Characteristics.
4. VSWR Measurement.
5. Impedance and Frequency Measurement.
6. Waveguide parameters measurement.
7. Scattering parameters of Magic Tee.
Part – B :
8. Characterization of LED.
9. Characterization of Laser Diode.
10. Measurement of Data rate for Digital Optical link.
11. Measurement of NA.
12. Measurement of losses for Analog Optical link.
Equipment required for Laboratories:
1. Regulated Klystron Power Supply
2. VSWR Meter -
3. Micro Ammeter - 0 – 500 μA
4. Multi meter
5. CRO
6. GUNN Power Supply, Pin Modulator
7. Reflex Klystron
Electronics & Communication Engineering 168
8. Crystal Diodes
9. Micro wave components (Attenuation)
10. Frequency Meter
11. Slotted line carriage
12. Probe detector
13. wave guide shorts
14. Pyramidal Horn Antennas
15. Directional Coupler
16. E, H, Magic Tees
17. Circulators, Isolator
18. Matched Loads
19. Fiber Optic Analog Trainer based LED
20. Fiber Optic Analog Trainer based laser
21. Fiber Optic Digital Trainer
22. Fiber cables - (Plastic, Glass)
Viva questions:
Now, from the relation, find free space wavelength 1/ λo =1/ λc +1/ λg
Calculation of λo=
1/ λo =1/ λc +1/ λg
Coupling factor C = 10log10(Pi /Pf)dB
Isolation I = 10log10(Pi /Pb)Db
RESULT: -----------------------------------------------------
PROCEDURE:
7.
Now adjust Pot P4 in fully clockwise position (intensity: HIGH) and
vary the distance.
8. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN indicated in the block diagram.
9. Mean radius is calculated as
DATA RATE
MEASUREMENT:
RESULT:
---------------------------------------------------------------------
THOERY:
communication
applications are available in the wave length regions 650 nm, 780 nm, 850 nm,
980 nm, 1300 nm and 1550.
To download the lab manual click on "CLICK ME": CLICK ME
List of experiments that are performed are listed below with requirements:
Part – A :
1. Reflex Klystron Characteristics.
2. Gunn Diode Characteristics.
3. Directional Coupler Characteristics.
4. VSWR Measurement.
5. Impedance and Frequency Measurement.
6. Waveguide parameters measurement.
7. Scattering parameters of Magic Tee.
Part – B :
8. Characterization of LED.
9. Characterization of Laser Diode.
10. Measurement of Data rate for Digital Optical link.
11. Measurement of NA.
12. Measurement of losses for Analog Optical link.
Equipment required for Laboratories:
1. Regulated Klystron Power Supply
2. VSWR Meter -
3. Micro Ammeter - 0 – 500 μA
4. Multi meter
5. CRO
6. GUNN Power Supply, Pin Modulator
7. Reflex Klystron
Electronics & Communication Engineering 168
8. Crystal Diodes
9. Micro wave components (Attenuation)
10. Frequency Meter
11. Slotted line carriage
12. Probe detector
13. wave guide shorts
14. Pyramidal Horn Antennas
15. Directional Coupler
16. E, H, Magic Tees
17. Circulators, Isolator
18. Matched Loads
19. Fiber Optic Analog Trainer based LED
20. Fiber Optic Analog Trainer based laser
21. Fiber Optic Digital Trainer
22. Fiber cables - (Plastic, Glass)
EXP NO.: 1 DATE:
CHARACTERISTICS OF GUNN
DIODE OSCILLATOR
AIM:
To verify the V-I characteristics
of Gunn Diode Oscillator
Equipment required:
1. Gunn power supply XGPS 610
2. Gunn oscillator XG 11
3. Pin modulator
4. Isolator XI 621
5. Variable attenuator XA 520
6. Crystal detector XD 451
7. Waveguide stand XU 535
8. CRO with probes
Theory:
Gunn diode oscillators circuits normally consists of
a resonant cavity, an arrangement for coupling diode to the cavity, a circuit
for biasing the diode and a mechanism to couple the RF power from cavity to
external circuit / load. A coaxial cavity or a rectangular waveguide cavity is
commonly used.
The most important mode of oscillation of Gunn
oscillator is limited space charge accumulation mode. This mode gives high
power coupled with high efficiency. In this mode the domain is not allowed to
form at all frequencies and RF voltages are so chosen that the domain do not
have sufficient time to form while the field above threshold. As a result, most
of the domains are maintained in the negative conductance stage during a large
part of voltage cycle. It is used in high power operations.
Procedure:
1.
Setup the experiment as shown in the
figure.
2. Keep the control knobs
of Gunn power supply as shown below.
a.
Meter switch-Off
b.
Gunn bias knob-Fully anti-clockwise
c.
Pin bias knob- Fully anti-clockwise
d.
Pin mode frequency-Any position
3.
Switch on the power supply.
4.
Measure the Gunn diode current corresponding to
various Gunn bias voltages through the digital panel meter of the Gunn power
supply by varying the Gunn bias knob.
5.
Do not exceed the Gunn bias voltage above 8 volts
6. Plot the voltage and current readings on the graph and
measure the threshold voltage corresponding to the maximum current.
 |
| SETUP FOR THE V-I CHARACTERISTICS OF GUNN DIODE OSCILLATOR |
MODEL GRAPH:
OBSERVATIONS:
S.No
|
Voltage (V)
|
Current(A)
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
|
||
PRECAUTIONS:
1.
Do not leave the Gunn bias knob at threshold position
for more than 10 to 15 sec because due to excessive heating, Gunn diode may burn.
2. The readings should be taken
without parallax error.
RESULT:
--------------------------------------------------------------
Viva questions:
1.
What are various modes of Gunn diode oscillations and
what factors determine the frequency of oscillations?
2.
What are the different materials used to manufacture Gunn diode?
EXP NO.:2
CHARACTERISTICS
OF REFLEX KLYSTRON
AIM:
To verify the characteristics of
Reflex klystron
EQUIPMENT REQUIRED:
1.
Klystron power supply XKPS 610
2.
Reflex klystron 2K25
3.
Isolator XI 621
4.
Variable attenuator XA
520.
5.
Frequency Meter XF 710
6.
Slotted line XS 651
7.
Tunable probe XP 655
8.
Crystal detector XD 451
9.
Waveguide stand XU 535
10.
Cooling fan
11.
CRO with probes
THEORY:
The Reflex klystron is a single cavity variable
frequency microwave generator oscillator. It has low power and low efficiency. It has electron gun similar to that of two
cavity klystron but it is smaller. As the size is small, the beam does not
require focusing. The two cavity klystron was not used because the oscillation
of frequency is varied. The resonant frequency of each cavity and phase shift
of feedback path should be readjusted for every positive feedback. Due to this
disadvantage, reflex klystron is used. They are used as local oscillator in
microwave experiments.
PROCEDURE:
1.
Setup the experiment as shown in figure.
2.
Keep the control knob of klystron power supply as shown below.
a.
MOD switch-AM
b.
Beam voltage knob-Fully Anti-clockwise
c.
Klystron repeller voltage- Fully clockwise
d.
AM amplitude knob-Fully clockwise
e.
AM frequency knob- Fully clockwise
3. Switch ON the klystron power
supply and cooling fan.
4.
Set the beam voltage at 250V with the help of beam voltage knob.
5.
Set the repeller voltage, AM amplitude & AM
frequency to obtain a square wave on the CRO.
6. Now, vary
the repeller voltage from minimum (not more than 100V) and note down the
corresponding voltage from CRO.
7. Find the power at P=V2 /R and plot the graph between output power and repeller voltage.
 |
| SETUP FOR CHARACTERISTICS OF REFLEX KLYSTRON |
OBSERVATIONS:
Repeller voltage(V)
|
Output Voltage (V)
|
Output Power P=V2R
|
PRECAUTIONS:
1.
The microwave source should be exposed to fan.
2.
Readings should be taken without parallax error.
RESULT:
---------------------------------------------------------------------
1.
Why pentode tubes are not suitable at high frequencies?
2.
What do you mean
by velocity and density modulations? How do these differ from frequency and
phase modulations?
EXP NO.:3 MEASUREMENT OF FREQUENCY AND IMPEDANCE
AIM:
To determine the frequency and
impedance of a rectangular waveguide
EQUIPMENT REQUIRED:
1. Klystron power supply
2. Reflex klystron
3. Variable Attenuator
|
XKPS 610
2K25
XA 520
|
|
4. Isolator
5. Frequency meter
|
XI 621
XF 610
|
|
6. Slotted line
7. Tunable probe
8. Crystal detector
|
XS 651
XP 655
XD 451
|
|
9. Waveguide stand
10. CRO and probes
|
XU 535
|
|
11. Cooling fan
|
||
THEORY:
|
The cutoff frequency relationship shows the physical
size of the waveguide will determine the propagation of particular mode of
specific order determined by the values of m
and n. The minimum cutoff frequency is obtained for a rectangular
waveguide having dimensions a>b for
values of m=1, n=0; TE10 is
called dominant mode since for TMnn modes
n≠0 the lowest order possible is TE10, called
the dominant mode in a rectangular waveguide
a>b.
|
For TE10 mode
the parameters λo, λg, λc related as 1/ λo =1/ λc
+1/ λg
λoà
free space wavelength
λgàguided wavelength
λcàcutoff wavelength
PROCEDURE:
1.
Setup the experiment as shown in figure.
2.
Keep the control knob of klystron power supply as shown below.
a.
MOD switch-AM
b.
Beam voltage knob-Fully Anti-clockwise
c.
Klystron repeller voltage- Fully clockwise
d.
AM amplitude knob-Fully clockwise
e.
AM frequency knob- Fully clockwise
3.
Switch ON the klystron power supply and cooling fan.
4.
Set the beam voltage at 250V with the help of beam voltage knob.
5.
Set the repeller voltage, AM amplitude and frequency to obtain a square
wave on the CRO.
6.
Tune the frequency meter in order to get a dip in the
signal. Note the frequency as ‘f’. Calculate
λ=c/f.
7.
Now , detune the frequency meter .
8.
Move the probe along along the slotted line to a
position when the signal is minimum (or) maximum. Note this as ‘d1’.
9.
Continue moving the probe until you get minimum or maximum. Now rate
reading as ‘d2’.
10.
Calculate d= d1- d2. Calculate the guided wavelength as twice the
impedance between between two successive maximum or minimum.λg=2d
Calculate d= d1- d2. Calculate the guided wavelength as twice the
impedance between between two successive maximum or minimum.λg=2d
11.
Measure the waveguide inner board dimensions ‘a’ which
will be around 22.86 mm and narrow dimension ‘b’ which is 10.5 mm.
12. Calculate the cutoff
wavelength asλc=2a
Now, from the relation, find free space wavelength 1/ λo =1/ λc +1/ λg
14. Wavelength of the waveguide
should be approximately equal to free space wavelength ‘λo’.
15.
Find the characteristic impedance as zo=377(b/a)( λg/λ)
 |
| SETUP FOR MEASUREMENT OF FREQUENCY AND IMPEDANCE |
OBSERVATIONS:
Beam voltage =
273 V Beam current = Repeller
voltage = Dip Frequency f = Wavelength λ=c/f=
Inner waveguide dimension a= 22.86mm
Outer waveguide dimension b= 10.5mm
dà difference between two successive maxima
or minima d1 =
d2 =
d= d2-d1 or d1-d2=
Guided wavelength
λg=2d= Cutoff wavelength λc=2a =
1/ λo =1/ λc +1/ λg
λo=
Characteristic
impedance = zo=377(b/a)( λg/λ) =
PRECAUTIONS:
1.
The microwave source should be exposed to fan.
2. Readings should be taken without
parallax error.
RESULT:
-----------------------------------------------------------------------------
Viva questions:
1.
What is the frequency range of X-band & C-band?
2.
What is the relation between λ0, λg, and λc in a rectangular wave guide?
3.
What parameters can be calculated using smith chart?
EXP NO.: 4
MEASUREMENT OF
WAVEGUIDE PARAMETRES
AIM:
To measure the parameters of a
rectangular waveguide
a.
Cutoff frequency
b.
Guided wavelength
c.
Group velocity
d.
Phase velocity
e.
Characteristic impedance
EQUIPMENT REQUIRED:
1.
Klystron power supply XKPS 610
2.
Reflex klystron 2K25
3.
Variable Attenuator XA 520
4.
Circulator isolator XI 621
5.
Frequency meter XF 610
6.
Slotted line XS 651
7.
Tunable probe XP 655
8.
Crystal detector XD 451
9.
Waveguide stand XU 535
10.
CRO and probes
11.
Cooling fan
THEORY:
Guide
wavelength (λg): It is
defined as distance travelled by the wave in order to undergo a phase shift of
2π radians.Phase velocity (vp): The wave propagates in the waveguide when
guide wavelength is greater than .It is defined as the rate at which wave
changes its phase in terms of guided wavelength. Group velocity (vg): It is defined as the rate at which the wave
propagates through the waveguide.
PROCEDURE:
1. Setup the experiment as
shown in figure.
2.
Keep the control knob of klystron power supply as shown below.
a.
MOD switch-AM
b.
Beam voltage knob-Fully Anti-clockwise
c.
Klystron repeller voltage- Fully clockwise
d.
AM amplitude knob-Fully clockwise
e.
AM frequency knob- Fully clockwise
3.
Switch ON the klystron power supply and cooling fan.
4. Set the beam voltage at 250V
with the help of beam voltage knob.
5.
Set the repeller voltage, AM amplitude and frequency
to obtain a square wave on the CRO.
6.
Tune the frequency meter in order to get a dip in the
signal. Note the frequency as ‘f’. Calculate
λ=c/f.
7.
Now , detune the frequency meter .
8.
Move the probe along along the slotted line to a
position when the signal is minimum (or) maximum. Note this as ‘d1’.
9. Continue moving the probe until you get minimum
or maximum. Now rate reading
as
‘d2’.
10. 
Calculate d= d1- d2. Calculate the guided wavelength as twice the
impedance between between two successive maximum or minimum.λg=2d
Calculate d= d1- d2. Calculate the guided wavelength as twice the
impedance between between two successive maximum or minimum.λg=2d
11. Measure the
waveguide inner board dimensions ‘a’ which will be around 22.86 mm and narrow
dimension ‘b’ which is 10.5 mm.
12.
Calculate the cutoff wavelength as twice the inner dimensions.λc=2a
|
| SETUP FOR MEASUREMENT OF waveguide parameters |
Find the characteristics
impedance as zo=377(b/a)( λg/λ)
13.
Calculate the group and phase velocities vg=(λ/λg)*c vp= (λg/ λ)*c
Beam voltage =
273 V Beam current = Repeller
voltage = Dip Frequency f = Wavelength λ=c/f=
Inner waveguide dimension a= 22.86mm
Outer waveguide dimension b= 10.5mm
dà difference between two successive maxima
or minima d1 =
d2 =
d= (d2-d1)or (d1-d2) =
Guided
wavelength λg=2d= Cutoff
wavelength λc=2a = Group
velocity vg=(λ/λg)*c = Phase velocity vp= (λg/ λ)*c =
Characteristic impedance = zo=377(b/a)(λg/λ) =
PRECAUTIONS:
1.
Microwave source should be exposed to
fan.
2.
Readings should be taken without parallax error.
RESULT:
--------------------------------------------------------------------
EXP NO.: 5
VERIFICATION OF CHARACTERISTICS OF MAGIC TEE JUNCTION
AIM:
To verify
the characteristics of Magic Tee junction
EQUIPMENT REQUIRED:
1. Klystron power supply XKPS 610
2. Reflex klystron 2K25
3. Variable Attenuator XA 520
4. Circulator
5. Frequency meter XF 610
6. Slotted line XS 651
7. Magic tee junction
8. Crystal detector XD 451
9. CRO with probes
10. Cooling fan
THEORY:
Magic Tee is a combination of E-plane Tee and H-plane Tee. If two waves
of equal magnitude and the same phase are fed into port1 and port2, the output
will be zero at E- arm and additive at H-arm. If a wave is fed into H-arm, it
will be divided equally between port1 and port2 of the collinear arms and will
not appear at E-arm. If a wave is fed into E- arm, it will produce an output of
equal magnitude and opposite phase at port1 and port2. The output at H-arm is
zero. If a wave is fed into one of the collinear arms at port1 or port2, it
will not appear in the other collinear arm at port2 or port1, appears at E-arm
which causes a phase delay while the
H-arm causes a phase advance.
PROCEDURE:
1.
Setup the equipment as shown in the figure.
2.
Keep the control knobs of Klystron Power supply as shown below
a.
Mod. Switch -- AM
b.
Beam voltage knob --
Fully
anticlockwise
c.
Repeller Voltage -- Fully clockwise
d.
AM amplitude knob -- Around Fully
anticlockwise
e.
AM frequency knob -- Fully clockwise
3. Switch ON the Klystron power
supply and cooling fan.
4.
Set the beam voltage at 250V with the help of beam voltage knob.
5.
Set the repeller voltage, AM amplitude and frequency
to obtain a square wave on the CRO.
6.
Connect crystal detector to the slotted line and note the input power
as Pi
7.
Now, connect the H arm of the Magic Tee junction to the slotted line.
8.
Connect matched termination to two arms and crystal
detector to the E arm and note the output power as P1
9. Now, connect the E arm of
the Magic Tee junction to the slotted line.
10. Connect
matched termination to two arms and crystal detector to the H arm and note the
output power as P2.
 |
| SETUP FOR MEASUREMENT OF MAGIC TEE PARAMETRES |
OBSERVATION:
Beam voltage =
Beam current = Repeller voltage =
Input power Pi = Vi2/R =
Vi=
R = 1W
|
Coupling factor of E-arm => P1 = V1
/R =
V1 =
R = 1W
C = 10log10(Pi/P1) dB =
|
Coupling factor of H-arm => P2 = V2 /R =
V2 =
R = 1W
C = 10log10 (Pi/P2) dB =
PRECAUTIONS:
1.
Microwave source should be exposed to
fan.
2.
Readings should be taken without parallax error.
3.
Avoid the exposing of body parts to the microwaves
RESULT:
---------------------------------------------------------
Viva
questions:
1.
What are the different applications of magic Tee?
2.
What is the difference between E-plane Tee and H-plane Tee?
EXP NO.: 6
CHARACTERISTICS OF DIRECTIONAL COUPLER
AIM:
To verify the characteristics of
Directional Coupler
EQUIPMENT REQUIRED:
1. Klystron power supply XKPS 610
2. Reflex klystron 2K25
3. Isolator XI 621
4. Variable Attenuator XA 520
5. Frequency meter XF 610
6. Slotted line XS 651
7. Tunable probe XP 655
8. Crystal detector XD 451
9. Directional coupler
10. Matched termination XL 400
11. Waveguide stand XU 535
12. CRO and probes
13. Cooling fan
THEORY:
Directional couplers are flange built in waveguide
assemblies which can sample a small amount of microwave power for measurement
purposes. They are designed to measure incident or reflected powers, SWR
values, providing a single path to the receiver or perform other desirable operations. They can be
unidirectional (measuring only incident power) or bidirectional (measuring both
incident and reflected powers). The waveguide is a 4-port waveguide junction.
PROCEDURE:
1.
Setup the experiment as shown in figure.
2.
Keep the control knob of klystron power supply as shown below.
a. MOD switch-AM
b. Beam voltage knob-Fully Anti-clockwise
c. Klystron Repeller voltage- Fully clockwise
d. AM amplitude knob-Fully clockwise
e. AM frequency knob- Fully clockwise
3.
Switch ON the klystron power supply and cooling fan.
4.
Set the beam voltage at 250V with the help of beam voltage knob.
5.
Set the Repeller voltage, AM amplitude and frequency to obtain a square
wave on the CRO.
6.
Connect the crystal detector to the slotted line and note the input
power as Pi.
7.
Now connect Port1 of directional coupler to the slotted line.
8. Connect the
matched termination to Port3 and crystal detector to the Port2. Note the reverse power as Pr.
9. Connect the
matched terminal to Port2 and crystal detector to Port3. Note the forward power as
Pf.
10. Now connect the Port2 of
directional coupler to the slotted line.
11. Connect
matched termination to Port1 and crystal detector to Port3. Note the backward
power as Pb.
12. Calculate the various
parameters of directional coupler.
Directivity D = 10log10(Pf /Pb)dB
Transmission loss TL=10log10(Pi /Pr)dB
Isolation I = 10log10(Pi /Pb)Db
 |
| SETUP FOR CHARACTERISTICS OF DIRECTIONAL COUPLER |
OBSERVATIONS:
Beam voltage =
Beam current = Repeller voltage = R=1Ω
Input power Pi= Vi2/R =
Forward power Pf= Vf2/R =
|
Backward power Pb=
Vb2/R = Received power Pr= Vr /R =
Coupling
factor C = 10log10(Pi /Pf)dB = Directivity D = 10log10(Pf /Pb)dB =
Transmission loss Tl =10log10(Pi /Pr)dB =
Isolation I = 10log10(Pi /Pb)dB = PRECAUTIONS:
1.
The microwave source must be exposed to fan.
2. Readings must be taken
without parallax error.
Viva
questions:
1.
What factors determine the parameters of directional coupler?
2.
Write down S-matrix of a directional
coupler?
EXP NO.:7 DATE:
MEASUREMENT OF
VSWR AND REFLECTION COEFFICIENT
AIM:
To determine
VSWR and Reflection coefficient for No load, matched termination and Horn
antenna.
EQUIPMENT REQUIRED:
1.
Klystron power supply XKPS 610
2.
Reflex klystron 2K25
3.
Variable Attenuator XA 520
4.
Circulator isolator XI
621
5.
Frequency meter XF 610
6.
Slotted line XS 651
7.
Tunable probe XP 655
8.
Matched termination XL 400
9.
Horn antenna
10.
Waveguide stand XU
535
11.
CRO and probes
12.
Cooling fan
THEORY: The
ratio of maximum to minimum voltages gives VSWR. It is given by
S= Vmax/Vmin = 1+ ρ /1- ρ
è S varies from 1 to ∞
è ρ means reflection coefficient.
The reflection
coefficient (ρ) is defined as the ration of power reflected to incident power.
ρ
= Preflected/Pincident
è ρ
varies from 0 to ∞
PROCEDURE:
1.
Setup the experiment as shown in figure.
2.
Keep the control knob of klystron power supply as shown below.
a.
MOD switch-AM
b.
Beam voltage knob-Fully Anti-clockwise
c.
Klystron Repeller voltage- Fully clockwise
d.
AM amplitude knob-Fully clockwise
e.
AM frequency knob- Fully clockwise
3.
Switch ON the klystron power supply and cooling fan.
4.
Set the beam voltage at 250V with the help of beam voltage knob.
5.
Set the Repeller voltage, AM amplitude and frequency
to obtain a square wave on the CRO.
6.
There is no load at the end of the slotted line. This is known as no
load condition.
7.
Move the probe along the slotted line and measure the
maximum and minimum levels of the signal and mark it Emax and Emin
respectively.
8.
Calculate VSWR and Reflection Coefficient as
VSWR(S) = Emax/
Emin Reflection
Coefficient (ρ) = S+1/S-1
9.
Repeat step 7 and 8 with load as Matched Termination and Horn antenna.
 |
| SETUP FOR MEASUREMENT OF VSWR AND REFLECTION COEFFICIENT |
OBSERVATIONS:
Beam voltage =
Beam current = Repeller voltage = No load:
Emax = Emin =
VSWR S = Emax/ Emin=
Reflection Coefficient ρ = S-1/S+1=
Matched termination:
Emax = Emin =
VSWR S = Emax/ Emin=
Reflection Coefficient ρ = S-1/S+1=
Horn antenna:
Emax = Emin =
VSWR S = Emax/ Emin=
Reflection Coefficient ρ = S-1/S+1=
PRECAUTIONS:
1.
Microwave source should be exposed to
fan.
2.
Readings should be taken without parallax error.
RESULT: ---------------------------------------------------------------------------------
Viva
questions:
1.
What is the significance of VSWR?
2.
What are the different methods to measure VSWR?
EXP NO.: 8
MEASUREMENT OF
LOSSES FOR ANALOG OPTICAL LINK
AIM: To determine the propagation loss
and bending loss of an optical fiber for 660 nm wavelength LED.
EQUIPMENT REQUIRED:
1.
Link-A kit.
2.
20 MHz Dual Trace Oscilloscope.
3.
1 & 3 Meter Fiber cable.
4. Power supply.
5.
Patch chords
THEORY:
Optical fibers are available in different variety of
materials. These materials are usually selected by taking into account their
absorption characteristics for different wavelengths of light. In case of
optical fiber, since the signal is transmitted in the form of light which is
completely different in nature as that of electrons, one has to consider the
interaction of matter with the radiation
to study the losses in fiber. Losses are introduced in fiber due to various
reasons. As light propagates from one end of fiber to another end, part of it
is absorbed in the material exhibiting absorption loss. Also part of the light
is reflected back or in some other directions from the impurity particles
present in the material contributing to the loss of the signal at the other end
of the fiber. In general terms it is known as propagation loss.
1. Slightly
unscrew the cap of 660 nm LED. Do not remove the cap from the connector. Once
the cap is loosened, insert a fiber into the cap and ensure that the fiber is
properly fixed. Now, tight the cap by screwing it back. Keep Pot P3 fully
anti-clockwise position.
2. Make the
connections and Jumper settings as shown in block diagram Connect the power
supply cables with proper polarity to kit. While connecting this, ensure that
the power supply is OFF.
3. Set the
sine wave with 1 KHz, 2 V(p-p)
amplitude and connect it to the IN post of analog buffer.
4.
Connect the other end of the fiber to analog detector.
5.
Switch on the power supply.
6. Observe the output signal
from the detector at ANALOG OUT post on CRO
by adjusting
INTENSITY Pot P3 in kit and you should get the reproduction of the original
transmitted signal. Mark this amplitude level as “V1”.
7. Now replace
1 meter fiber by 3 meter fiber without disturbing any of the previous settings.
8. Measure the
amplitude level at the receiver side again. Mark this as V2. You will notice that V2< V1.If ‘α’ is the attenuation of the
fiber then we have,
αdB= (10/L1-L2)log10(V2-V1)
where α = dB/km
L1= fiber length of 1m cable L2= fiber length of 3m cable
BENDING LOSS:
1.
Repeat all the steps from 1 to 8
2.
Bend the fiber in a loop as shown in block diagram
Measure the amplitude of the received signal.
3.
Keep reducing the diameter to about 2 cm (Do not
reduce loop diameter less than 2 cm)
& take corresponding output voltage readings.
 |
| SETUP FOR LOSS MEASUREMENT: |
OBSERVATIONS: ATTENUATION MEASUREMENT:
Input voltage (V) = 2Vp-p V1= voltage of 1m fiber = V2 = voltage of 3m fiber = L1
= 1m
L2 = 3m
adB= (10/L1-L2)log10(V2/V1)=
BENDING LOSS:
V1= 2Vp-p, L1=1m
S.No
|
Diameter (cm)
|
Output voltage (Vo)
|
Bending loss
|
1
2
3
|
PRECAUTIONS:
1.
Keep the jumpers properly
2.
Select the patch cards according to the requirement and insert properly
3.
Avoid the sharp bending of optical fiber cable
RESULT:
--------------------------------------------------------------------
Viva
questions:
1.
What are the different types of losses of optical communication?
2.
Distinguish between attenuation distortion and delay distortion.
EXP NO.: 9
CHARACTERISTICS
OF LED (660)
AIM:
To
verify the V-I characteristics of fiber optic LED of wavelength 660 nm
EQUIPMENT:
1. Link-A kit.
2. 20 MHz Dual Trace Oscilloscopes.
3.
1 & 3 Meter Fiber cable.
4. Power supply.
5.
Voltmeter.
6. Current meter.
7. Jumper Connecting Wires-4.
THEORY:
For optical communication
requiring bit rates less than approximately 100-200 Mbps
together with multimode fiber-coupled optical power in the tens of
microwatts, semiconductor light-emitting diodes (LED’s) are usually the best
light source choice. These LED’s require less complex drive circuitry than
laser diodes since no thermal or optical stabilization circuits are needed and
they can be fabricated less expensively with higher yields..
PROCEDURE:
1. Make the
jumper and switch settings as shown in the jumper diagram. Keep pot P4 in fully
clockwise position.
2. Connect the
ammeter with the jumper connecting wires (provided along with the kit) in
jumpers JP3 as shown in the diagram.
3. Connect the
voltmeter with the jumper wires to JP5 and JP2 at positions as shown in the
diagram.
4. Connect the
ammeter with the jumper connecting wires (provided along with the kit) in
jumpers JP7 as shown in the diagram.
5. Switch on
the power supply. Keep the potentiometer P3 in its minimum position (fully
anticlockwise position), P4 is used to control biasing voltage of the LED.
6. To get the
VI characteristics of LED, rotate P3 slowly
and measure forward current and corresponding forward voltage of the LED.
7.
Take number of such readings for forward voltage, forward current &
optical power.
8. Plot the graph of forward
voltage Vs forward current using the values noted.
 |
| SETUP FOR V-I CHARACTERISTICS OF FIBER OPTIC LED(660nm) |
OBSERVATIONS:
S.No.
|
Forward voltage of LED (Vf) volts
|
Forward current of LED (If) mA
|
1
2
3
4
5
6
7
8
9
10
|
PRECAUTIONS:
1.
Keep the jumpers properly
2. Select the patch cards
according to the requirement and insert properly
3. Avoid the sharp bending of
optical fiber cable
RESULT:
------------------------------------------------------------------------
Viva questions:
1.
Mention the important semiconductors used in LED’s and laser.
2.
How does the LED work?
3.
Define internal quantum efficiency of a LED or laser.
EXP NO.: 10 DATE:
MEASUREMENT OF
NUMERICAL APERTURE
AIM: To measure the numerical aperture
of optical fiber using 660 nm Wavelength LED.
APPARATUS:
1.
Link-A kit.
2.
1 Meter Fiber cable.
3. NA JIG.
4.
Steel Ruler.
5. Power supply
THEORY:
Numerical aperture refers to the maximum angle at which the light
incident on the fiber end is totally internally reflected and is transmitted
properly along the fiber. The alignment of optical source with respect to the
inlet of optical fiber is a crucial factor for propagation of light through
reflection. The angle subtended by the source should be such that light suffers
total internal reflection when it strikes the inner surface of the fiber.
PROCEDURE:
1. Slightly
unscrew the cap of 660 nm LED. Do not remove the cap from the connector. Once
the cap is loosened, insert the fiber into the cap. Now, tight the cap by
screwing it back.
2. Connect the
power supply cables with proper polarity to the kit. While connecting this,
ensure that the power supply is OFF. Do not apply any TTL signal from Function
Generator. Make the connections as shown in block diagram.
3.
Keep Pot P3 in fully clockwise position and P4 in fully anticlockwise position.
4.
Switch “ON” the power supply.
5.
Insert the other end of the fiber into the NA JIG.
6. Keep the
distance of about 1 cm between the fiber tip and the screen and vary the
intensity (HIGH, MEDIUM, LOW).
8. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN indicated in the block diagram.
9. Mean radius is calculated as
r = (MR + PN) / 4
. Find the
numerical aperture of the fiber using the formula. NA = sin θmax = Where
d= OA
 |
| SETUP OF NUMERICAL APERTURE |
OBSERVATIONS:
a.
Intensity is constant: HIGH
Intensity is constant: HIGH
S.No
|
Distance(cm)
|
MR(cm)
|
PN(cm)
|
r=(PN+MR)/4
|
NA = r /
|
1.
2.
3.
|
|||||
b.
Distance is constant = 1 cm
Distance is constant = 1 cm
S.No
|
Intensity
|
MR(cm)
|
PN(cm)
|
r=(PN+MR)/4
|
NA = r /
|
1.
2.
3.
|
HIGH
MEDIUM LOW
|
PRECAUTIONS:
1.
Keep the jumpers properly
2.
Select the patch cards according to the requirement and insert properly
3. Avoid the sharp bending of
optical fiber cable
RESULT: ---------------------------------------------------------------------------------
Viva questions:
1)
Define NA?
2)
Give the formula for Numerical Aperture.
EXP NO.: 11
MEASURMENT OF
DATA RATE FOR DIGITAL OPTICAL LINK
AIM:
To connect the RS-232 ports of two computers using
optical fiber digital link to establish a full duplex communication and to
measure the data rate at different parity bits, stop bits and data bits.
APPARATUS REQUIRED:
a.
Fiber link- A kit
b.
1mt fiber cable
c. 9-pin D connector cables (2)
d.
Computers PC/XT, PC, 386, 486 (or) higher version
e. Power supply
f. Patch chords
THEORY:
In optical communication the exchange of information
between any two devices across a communication channel involves some type of
optical signal which carries the information. The rate at which circuits (or)
other devices operate when handling digital information is called data rate.
The max rate that can be obtained over a given channel is called channel
capacity in digital link, input is a digital signal. The optical communication
involves exchange of information between any two devices across a communication
channel. The data rate can be measured
by connecting optical digital link to the computer
PROCEDURE:
1.
Slightly unscrew the cap of 660nm LED on kit. Don’t
remove the cap from the connector. Once
the cap is loosened, insert the fiber into the cap. Now, tight the cap by
screwing it back.
2.
Make the jumper settings and connection diagrams as
shown in figures 1 and establish full duplex
communication.
3.
Refer to fig.2 of this experiment and make the
necessary connections and connect one
end of the 9 to 9 pin cable to PC COM 1 port and the other end to CN1
connector on LINK-A kit then connect second 9 to 9 pin cable one end to second
PC COM 1 port and other end to CN2 connector on LINK-A kit. Connect the power
supply cables with proper polarity to kit. While connecting this, ensure that
the power supply is OFF.
4.
Connect CN1 post on the kit (RS-232 section) to IN post of digital
buffer section.
5.
Connect CN2 post on the kit (RS-232 section) to TTL OUT post of the
receiver section.
6.
Switch ON the PCs and the power supply of the kit fiber link-A.
7.
After putting ON one of the PC, go to START menu,
PROGRAMS, ACCESSORIES, COMMUNICATION and then click on HYPER TERMINAL.
8.
A new window will open, where in you double click on
HYPERTERM, two windows will open, one at the background and another with title
connection description which will be active.
9.
Enter the name in the box by which you would like to store
your connections, for e.g. (PC 2 PC) and click Ok. Also you could select the
ICON provided below. The background window title will change to the name
provided by you.
10.
Then specify connect using selecting direct to COM1 or
port where your cable is connected and then click on OK.
11.
Now window with title COM1 properties will appear,
where port setting should be done as shown below click on OK
12. After the above settings you
click OK. The background window will become
active.
13.
Click on file, save as, and save it in the directory, which you want.
14.
Perform the same procedure i.e.., from points 8 to 14
on the computer with whom we want to communicate.
15.
To start communicating between the two PC’s click on
the transfer menu and again click on send file. A window will be prompted
having title send file name with filename and protocol.
16.
Select “browse” for the file which we would like to
send to the PC connected. Select the file and click on open the file name and
address will be displayed in the small window. Then select the “Kermit”
protocol (optional use protocols are S-modem, Y-modem and IKX modem).
17.
To receive the file on the PC click on the transfer
menu and click on receive file. A window will be prompted having title
receiving file with location at which you want to receive files and protocol.
18.
Select the browser for the location where you would
like to store received files. Select the folder and click OK, the folder name
and address will be displayed in the small windows protocol to be selected
should be Kermit and select and same as the file transmitting PC.
19.
On the PC from which the selected file to be
transmitted, click on send. A new window will open showing file transfer
status. Immediately at the receiving PC click receive (otherwise time out error
will be displayed and communication will fail). You will see a window showing
the file is received in the form of packets.
20.
After the file is transferred both the windows in the
two PC’s will close. Check for the received files in the folder where the file
is stored. You can do this procedure vice versa to transfer the file.
 | |
|
OBSERVATIONS:
FULL DUPLEX COMMUNICATION:
Input characters
from keyboard 1 of PC1: MICROWAVE & OPTICAL COMMUNICATION LAB
Input characters from keyboard 1
of PC1 are displayed on PC2:
Output
characters of PC2: MICROWAVE & OPTICAL COMMUNICATION LAB Input characters
from keyboard 2 of PC2: ECE Department
Output
characters from keyboard 2 of PC2 are displayed on PC1: Output characters of
PC1: ECE Department
S.No
|
Baud rate
|
Tx time
|
Tx CPS
|
Rx time
|
Rx CPS
|
Stop bits
|
Data bits
|
Parity bits
|
1
|
||||||||
2
|
||||||||
3
|
PRECAUTIONS:
1.
Keep the jumpers properly
2. Select the patch cards according
to the requirement and insert properly
3.
Avoid the sharp bending of optical fiber cable
4.
Insert properly RS 232 probe between PC and optical trainer kit
Viva
questions:
1.
What are the different types of transmission systems used in the communication?
2.
What is baud rate?
3.
What is data rate?
EXP NO: 12
CHARACTERISTICS
OF LASER DIODE
AIM:
The aim of the experiment is to
study
a.
Optical Power (Po) of Laser Diode vs Laser Diode Forward Current (IF)
b.
Monitor Photodiode Current(IM) VS Laser Optical Power Output(Po)
APPARATUS REQUIRED:
1.
Laser Diode Transmission KitTX Unit
2.
Laser Diode Transmission Kit RX Unit
3.
Power supply
4.
Two-meter PMMA Fiber Patch cord (cable
1)
5.
Digital Multi Meter
6.
Patch chords
LEDs and Laser Diodes are the commonly used in
optical communication systems, whether the systems transmits digital or analog
signals. Laser Diodes (LDs) are used in telecom, data-com and video
communication applications involving high speeds and long hauls. All single
mode optical fiber communication systems use laser in the 1300 nm and 1550 nm
windows. Lasers with very small line-widths also facilitate realization of
wavelength division multiplexing (WDM) for high density communication over a
single fiber. The inherent properties of LDs that make them suitable for such
applications are, high coupled optical power in to the fiber (typically greater
than 1 mw), high stability of optical intensity, small line-widths (less than
0.05 nm in special devices), high speed (several GHz) and high linearity (over
a specified region suitable for analog transmission). Special lasers also
provide for regeneration/amplification of optical signals within an
optical fiber. These fibers are
known as
“erbium doped fiber
amplifiers. LDs for
Specifications of the Laser
Module @25C
Symbol
|
Parameter
|
Typical
|
Unit
|
*Po
|
Cw output power
|
2.5
|
mW
|
*lop
|
Operating Current
|
30
|
mA
|
*Wp
|
Wavelength at peak emission
|
650
|
Nm
|
*MTTF
|
Mean time to failure
|
10,000
|
Hrs
|
Po vs. IF EXPERIMENT:
The schematic diagram for study of the LD Po as a function of LD forward
current IF is shown below and is self-explanatory.
Procedure:
1.
Connect the 2-metre PMMA FO cable (cab 1) to TX Unit and couple the
laser light to the power meter on the RX unit as shown fig. Select ACC mode of operation.
2.
Set DMM1 to the 2000 mV range and on the RX side connect to the
terminals marked Po to it. Turn it on. The power meter is now ready for use.
Po= (reading)/10 dBm.
3.
Set DMM2 to the 2000 mV range and connect it between Vo and Gnd on the
TX unit. (IF
= Vo/100).
4.
Adjust the Set IF Knob to the extreme anticlockwise position to reduce
IF to 0. The power meter reading will
normally be below -40 dBm or out of range.
5.
Gradually increase IF. Note
IF and Po readings.
6.
Plot the graph Po Vs. log IF as shown in the Fig. 2.
7.
Determine the slopes prior to lasing and after lasing. Record the laser
threshold current.
 |
| Set up for Po Vs IF Measurement |
Observation table:
Sl.no
|
Vo(mV)
|
IF=Vo/100(mA)
|
Po(dBm)
|
1.
|
|||
2.
|
|||
3.
|
|||
4.
|
|||
5.
|
|||
6.
|
|||
7.
|
|||
8.
|
|||
9.
|
Precautions:
1.
Avoid the wrong and loose connections
2.
Avoid the exposing of body parts to the laser beam
Result: --------------------------------------------------------
Viva
questions:
1.
What are the characteristics of laser
radiation?
2.
What are the factors that decrease the life time of laser diode?
3.
What is meant by threshold condition for laser oscillation?
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