mw lab final
TRANSCRIPT
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
LIST OF EXPERIMENTS
S.NO. NAME OF THE EXPERIMENT PAGENO
1. REFLEX KLYSTRON CHARACTERISTICS 5
2. V-I CHARACTERSTICS OF GUNN DIODE 9
3. ATTENUATION MEASUREMENT 13
4. DIRECTIONAL COUPLER CHARACTERISTICS 17
5. MEASUREMENT OF VSWR 21
6. IMPEDANCE AND FREQUENCY MEASUREMENT 25
7. SCATTERING PARAMETERS OF CIRCULATOR 29
8. CHRACTERISTICS OF LED 33
9. LASER DIODE CHARACTERISTICS 37
10. INTENSITY MODULATION OF LASER OUTPUT THROUGH
AN OPTICAL FIBRE 43
11. MEASUREMENT OF NUMERICAL APERTURE 47
12. MEASUREMENT OF LOSSES FOR ANALOG OPTICAL LINK 51
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 1
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 2
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
LAB INTERNAL EVALUATION
S.No Name of the Experiment Date Remarks
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Klystron Power Supply
Klystron Mount &Tube Supply
Isolator Frequency Meter
Variable Attenuator
Detector Mount
Milli Ammeter
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
OBSERVATIONS:Mode Repeller-
Voltage (V)Output Current (mA)
Frequency (GHz)
Power=i2R(µW)(assume R=1)
1
2
3
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
REFLEX KLYSTRON CHARACTERISTICS
AIM: To study the characteristics of the reflex klystron tube.
1. Repeller Voltage Vs Output power.
2. Repeller Voltage Vs Frequency.
APPARATUS:
1. Klystron Power Supply
2. Klystron Mount
3. Klystron Tube
4. Isolator
5. Frequency Meter
6. Variable Attenuator
7. Detector Mount
8. Milli Ammeter
9. BNC cable
THEORY:
The reflex klystron makes use of velocity modulation to transform a continuous electron
beam into micro power. Electron emitted from the cathode are accelerated and passed through the
positive resonator towards negative reflector, which retards and finally reflects the electron and
electron turns back through the resonator. Suppose an electric field exists in the resonator, the
electron travelling forward will be accelerated or retarded as the voltage at the resonator changes
in amplitude. The accelerated electron leaves the resonator at an increased velocity. The electron
retarded will leave at reduced velocity. The electron leaving the resonator will need different time
to return, due to change in velocities. As a result, returning electrons group together in bunches. If
the bunches pass through grid at such time that the electrons are slowed down by the voltage,
energy will be delivered to the resonator and the klystron will oscillate.
PROCEDURE:
CARRIER WAVE OPERATION
1. Connect the components and equipments as shown in the figure.
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MODEL GRAPH:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 6
MODES OF KLYSTRON TUBE
Frequency (GHz)
Out put Power (ΜW)
Repeller Voltage (V)
Repeller Voltage (V)
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
2. Keep the variable Attenuator at the minimum attenuation position.
3. Set the MOD switch of klystron power supply at CW position, beam voltage control
knob to fully anti clockwise.
4. Rotate the frequency meter fully to one side.
5. Connect the AC milli ammeter with detector mount.
6. Switch “ON” the Klystron power supply and cooling fan for the klystron tube.
7. Put ON beam voltage switch (HT) and rotate the beam voltage knob clock wise slowly up
to 300V meter reading and observe beam current position. (The beam current should not
exceed 30mA). Do not change the Beam voltage while taking the reading
8. Change the repeller voltage slowly and watch milli ammeter for maximum deflection in
the ammeter.
9. Tune the plunger of Klystron mount for the maximum output.
10. Rotate the knob of frequency meter slowly and stop at that position where there is lowest
output current on milli ammeter. Read directly the frequency meter between two
horizontal lines and vertical marker. If micrometer type frequency meter is used read the
micrometer reading and use the frequency calibration chart.
11. Change the repeller voltage and read the current and frequency for each repeller voltage to
get three different modes of the Klystron.
PRECAUTIONS:
Change the frequency meter reading to minimum position after every reading of milli
ammeter. Let the beam current not to exceed 30mA
RESULT:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 7
Gunn Power Supply
Gunn oscillator
Pin modulator
Frequency Meter Detector mount
mountMount
Micro ammeter
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
OBSERVATIONS:
Frequency of operation of gunn diode:
GUNN BIAS VOLTAGE(V) GUNN DIODE CURRENT(µA)
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
V-I CHARACTERISTICS OF GUNN DIODE
AIM: To study the characteristics of Gunn – oscillator
APPARATUS:
1. Gunn Power Supply
2. Gunn Oscillator
3. Pin modulator
4. Detector Mount
5. Wave Guide Stands
6. BNC Cables and TNC Cables
7. Micro Ammeter
THEORY:
A Gunn diode, also known as transferred electron device (TED) is a form of diode used in
high frequency electronics. In gunn diode, there exists three regions: Two of them are heavily N-
doped on each terminal, with a thin layer of lightly doped material in between. When a voltage is
applied to the device, the electrical gradient will be largest across the middle layer.
Gunn diode with negative resistance characteristics can be used as an amplifier similar to
tunnel diode but are very popular.
Gunn diode oscillator circuit 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 the cavity to the external circuit as load. A coaxial cavity or a rectangular waveguide
are commonly used.
The circuit using coaxial cavity has the Gunn diode mounted at one end of the cavity
along with the central conductor of the coaxial line. The output is taken using a inductively or
capacitively coupled probe. The length of the cavity determines the frequency of oscillator.
PROCEDURE:
1. Set the components as shown in the figure.
2. Keep the control knobs of Gunn power supply as below
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MODEL GRAPH:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 10
VTH
Voltage ( V)
Current (µA) Threshold Voltage
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
a. Meter Switch - OFF
b. Pin Bias Knob - Fully Anti clockwise
c. Gunn Bias Knob - Fully Anti clockwise
d. Pin Mod Frequency - Any position
3. Set the micrometer of Gunn Oscillator for the required frequency of operation.
4. Switch ON the Gunn Diode power supply.
5. Measure the Gunn Diode current corresponding to the various
a. Gunn Diode bias voltage through the digital panel meter and meter switch,
b. Do not exceed bias voltage above 8V.
6. Plot the voltage and current reading on the graph.
RESULT:
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
BLOCK DIAGRAM:
G
OBSERVATIONS:
VSWR reading before placing test attenuator (Pin) ---------- (dB)
VSWR reading after attenuation (P0) ---------- (dB)
Therefore attenuation (P in-P0) ---------- (dB)
Micrometer
Reading(mm)
VSWR meter
Reading
P0(dB)
Attenuation(dB)
Pin-P0
EXPT NO: DATE:
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Klystron Power
supply
Klystron mount tube Isolator Variable Attenuator
Frequency meter
Test Attenuator
VSWR Meter
Detector Mount
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
ATTENUATION MEASUREMENT
AIM: 1) TO study the characteristics of variable attenuator.
2) To measure the attenuation of the test attenuator
APPARATUS:
1. Micro Wave Source ( Klystron Tube)
2. Klystron Power Supply ( XB-8010)
3. VSWR Meter
4. Detector Mount
5. Isolator
6. Frequency Meter
7. Variable Attenuator
8. Test Attenuator
9. Cooling Fan
THEORY:
The attenuator is two port bidirectional device, which attenuates same power when
inserted into the transmission line.
Attenuation, A(dB) = 10 log (P1/P2)
Where P1 = power observed or detected by the load without the attenuator in the line.
P2 = power observed or detected by the load with attenuator in the load.
Amount of attenuation can be measured in two methods.
1. Power ratio method
2. RF substitution method.
PROCEDURE:
1. Let the beam voltage be 300V.
2. Now vary the repeller voltage, amplitude and frequency knobs of klystron supply to
maximum power.
3. Note the readings of RANGE (dB) SWITCH without TEST ATTENUATOR. This is the
VSWR reading before attenuation.(Pin)
MODEL GRAPH:
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Attenuation
(dB)
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
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Micrometer Reading (mm)
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
4. Now slowly vary the variable Attenuator in steps of 0.5mm of micrometer reading and
tabulate the corresponding VSWR meter reading. Let it be Po.
5. Pin-P0 gives the attenuation factor.
6. Plot the attenuation factor Vs micrometer reading & obtain the characteristics.
7. Place the TEST ATTENUATOR (3 dB) whose attenuation to be measured, between
variable attenuator and detector mount without disturbing the set up. Note down the power
in VSWR meter for different positions of variable attenuator.
8. The difference between the powers gives the attenuation factor of the test attenuator
RESULT:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 15
Directional Coupler
Matched termination
Detector Mount
Directional Coupler
Microwave Source
Isolator Frequency Meter
Variable Attenuator
Detector Mount
Matched termination
Detector Mount
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 16
1 2
3
2
31
VSWR meter
VSWR meter
VSWR meter
Port 1 Port 2
Port 3
Port 4
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
DIRECTIONAL COUPLER
AIM: To measure the Directivity & coupling factor
APPARATUS:
1. Micro Wave Source
2. Isolator
3. Multi hole Directional Coupler
4. Detector Mount
5. Frequency Meter
6. Matched Termination
7. Variable Attenuator
8. Wave Guide Stands
9. VSWR Meter
10. BNC Cables
11. Slotted Line
THEORY:
Directional couplers are flanged, built in waveguide assemblies which can sample a small
amount of microwave power for measurement purposes. They can be designed to measure
incident and/or reflected powers, SWR (standing wave ratio) values, provide a signal path to a
receiver or perform other desirable operations. They can be unidirectional or bidirectional powers.
In its most common form, the directional coupler is a four port waveguide junction consisting of a
primary main waveguide and a secondary auxiliary waveguide. A portion of power travelling
from port 1 to port 2 is coupled to port 3 but not to port 4. Similarly, a portion of power travelling
from port 2 to port 1 is coupled to port 4 but not to port 3.
PROCEDURE:
1. Set the components as shown in figure.
2. Energize the microwave source for particular frequency of operation so that maximum
power can be obtained in VSWR meter without Directional Coupler.
3. Set any reference level of power in VSWR meter with the help of variable attenuator, gain
control knob of VSWR meter and note the reading that is Pin(dB)
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FORMULAE:
DIRECTIVITY = P in- P12 (dB)
COUPLING FACTOR = Pin-P13 (dB)
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
4. Insert the directional coupler with detector mount to the auxiliary port 3 and matched
termination to port 2, without changing the set up and position of variable attenuator and
gain control knob of VSWR meter. Note the readings of VSWR meter on the scale with
the help of range switch if required. let be P13(dB)
5. Calculate the coupling factor, by using the relation Pin-P13(dB)
6. Disconnect the detector mount from auxiliary port 3 and matched termination from port 2.
Then connect the matched termination to port 3 and detector mount to port 2 and measure
the reading in VSWR meter. let it be P12.
7. Calculate the directivity by using the relation Pin-P12(dB)
.
PRECAUTIONS:
1. Avoid loose connections.
2. Readings should be taken without any parallax error
RESULT:
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Klystronmount tube
Frequency meter
Tunable Probe
Variable attenuator
Slotted line carraige
Klystron Power Supply
VSWR meter
meterMeter
Matched load
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 20
Coaxial Cable
Short end load
K – band waveguide
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
MEASUREMENT OF VSWR
AIM: To determine the standing wave ratio and reflection coefficient.
APPARATUS:
1. Klystron Power supply
2. Klystron mount
3. Variable Attenuator
4. VSWR Meter
5. Matched Termination
6. Slotted Line Section
7. Detector Mount
8. Isolator
9. Frequency meter
10. Tunable probe
11. Wave guide stands
12. BNC cable
THEORY:
Any mismatched load leads to reflected waves resulting in standing waves along the
length of the line. The ratio of maxima to minima is defined as SWR. The maximum field
strength is found where two waves are in phase and minimum where the two waves add in
opposite phase. The distance between tow successive minimum or maximum is half the guided
wavelength on the line. The ratio of electric field strength of reflected and incident wave is called
reflection coefficient.
The voltage standing wave ratio (VSWR) is the ratio between max and min field strength
along the line
S= Emax/Emin= |Ei|+|Er||Ei|−|Er|
Reflection coefficient, ρ=ErEi
ρ=Z−ZoZ+Zo
Where Z= impedance at a point on line
Z0 = characteristic impedance
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
|ρ∨¿= S−1S+1
is obtained from above equation.
OBSERVATIONS AND CALCULATIONS:
Double minima method:
d1 =
d2 =
g = 2 (d2 – d1) =
d3 =
d4 =
VSWR = g / (d3 – d4) =
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PROCEDURE:
VSWR < 10
1. Arrange the equipment as in the figure with the slotted line terminated with 50ohm load.
2. Energize the klystron supply and adjust the microwave source and gain and coarse
knobs of VSWR meter to obtain the full deflection in VSWR meter.
3. Slowly rotate the slotted line probe carriage towards source so that the deflection in
VSWR meter is towards null deflection. Use range db switch in VSWR meter if
required.
4. Note down the reading in VSWR meter in SWR scale at minimum deflection.
VSWR > 10(double minima method)
1. Arrange the equipment as shown in the figure by connecting a short end load to the
slotted line section.
2. Energize the klystron power supply and adjust the gain and coarse knobs of VSWR
meter to obtain the full deflection.
3. Slowly rotate the slotted line probe carriage towards source and note down the reading
on the scale at the first minimum deflection. Let it be d1.
4. Repeat the above step and note down the reading at next minimum deflection. Let it be
d2.
5. Calculate the guided wavelength g, by the relation g = 2 (d2 – d1).
6. Now adjust the VSWR meter deflection to 3dB position using gain or coarse knobs of
VSWR meter.
7. Note down the reading on VSWR scale by moving slotted line probe carriage towards
source and load at 3 dB variation. Let them be d3 and d4 respectively.
8. Calculate the VSWR by the relation VSWR = g / (d3 – d4)
RESULT:
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
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K-Band Wave Guide
SS tuner
Matched load
Coaxial Cable
Klystron mount
Frequency meter
Probe Detector
Variable attenuator
Slotted Line Carriage
Klystron Power Supply VSWR
Meter
Movable shot
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
IMPEDANCE AND FREQUENCY MESUREMENT
AIM: To measure the unknown impedance – using Smith Chart
APPARATUS:
1. Klystron Power supply
2. Klystron mount
3. Variable Attenuator
4. VSWR Meter
5. Frequency Meter
6. Slotted Line Section
7. SS Tuner
8. Detector Mount
9. Matched load
10. Short end load
11. Cooling Fan
THEORY:
The impedance at any point on a transmission line can be written in the form of R+jX. For
comparison SWR can be calculated as S=1+¿ ρ∨ ¿1−¿ ρ∨¿¿
¿ , ρ = Z−ZoZ+Zo
The measurement is determined in the following way. The unknown device is connected
to the slotted line and the position of minima is determined. The unknown device is replaced by
movable short to the slotted line. Two successive minima position are noted. The twice of
difference between minima position will be guided wavelength.
One of the minima is used as a reference for impedance measurement find the difference
of reference minima and maxima position obtained by unknown load. Let it be d. Take smith
chart and draw a circle with radius S (VSWR) from the centre. Make a point on circumference of
smith chart towards load side at the distance equal to d/λg . Join the centre with point. Find the
point where it cuts the drawn wide. The coordinates of this point will show the normalized
impedance of load.
PROCEDURE:
1. Arrange the equipment as shown in the figure by connecting a short end load to the
slotted line section.
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
FORMULAES:
O = 2a where a is the length of the wave guide
g = 2(d2 – d1)
1 / o2 = 1 / g2 + 1 / c
2
g = Wave guide wavelength
c = Cutoff Wavelength
f=c/
OBSERVATIONS:
LO = Free space Wavelength
Zunknown = Zslot | R + j XL | OR Zslot | R - j XC| =
Zslot = / 1 – (o/c)2
=
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 26
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
2. Energize the klystron power supply and adjust the gain and coarse knobs of VSWR
meter to obtain the full deflection.
3. Slowly rotate the slotted line probe carriage towards source and note down the reading
on the scale at the first minimum deflection. Let it be d1.
4. Repeat the above step and note down the reading at next minimum deflection. Let it be
d2.
5. Calculate the guided wavelength g, by the relation g = 2 (d2 – d1).
6. Now replace the short end load and place the component SS tuner terminated with
matched load whose impedance is to be measured.
7. Adjust the VSWR meter to full deflection and measure the VSWR of the component.
Let it be S. And also note the reading on the scale, let it be dx.
8. Draw a circle on the Smith chart with radius of S.
9. Draw a line from the centre of the circle to d0/ λg depending on the load where d0=dx˜d1
10. Follow the reactance line from where the circle cuts the straight line which gives XL or
XC.
11. Also calculate the resistive component R by drawing a straight line onto the axis.
12. Using the following relations measure the impedance of the load.
RESULT:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 27
2Matched termination
Detector Mount
Gunn supply
Gunn oscillator
Pin modulator
Frequency meter
3 – port Circulator
VS WR Meter
Variable Attenuator
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 28
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT: DATE:
SCATTERING PARAMETERS OF CIRCULATOR
AIM: To measure the power flow in a circulator and derive the scattering matrix Parameters
APARATUS:
1. Gunn oscillator and power supply.
2. Variable attenuator
3. Frequency meter.
4. Circulator.
5. VSWR meter.
6. Matched termination.
7. Detector mount
THEORY:
Circulator is a ferrite device. It works on the principle of Faradays principle. It may have
any ports there is no restriction, commonly we use 3 or 4 ports. The wave will be moving only in
clockwise direction. Assume three port circulator, if we apply the input at port 1, it gives the
output at port 2, there is no power at port 3. Similarly if we apply the input at port 2, it gives the
output at port 3, there is no power at port 1.
PROCEDURE:
1. Connect the setup as shown in figure.
2. Switch on the oscillator power supply
3. Measure the input power without connecting circulator i.e. P in (dB) = P11(dB)
4. Connect the port 1 of circulator to slotted line while port 3 is matched terminated i.e.,
P12(dB).
5. Now port 2 is terminated & measure power at port 3 i.e. P13 (dB).
6. Similarly give input to port 2 & measure o/p at port 1&3 by terminating remaining ports.
7. Repeat the same procedure for port 3
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
OBSERVATIONS:1. Operating frequency =
2. Incident power
P1 1 = Pin
P12 =
P13 =3. Incident power
P22 = Pin
P23 =
P21 =
4. Incident power
P33 = Pin
P31 =
P32 =The scattering parameters are
S21 = (P22/P21)1/2 =
S23 = (P22/P23)1/2 =
S12 = (P11/P12)1/2 =
S13 = (P11/P13)1/2 =
S31 = (P33/P31)1/2 =
S32 = (P33/P32)1/2 =
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 30
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
RESULT:
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
CHARACTERISTICS OF LED
AIM:
1. Design and study of fiber optic analog link.
APPARATUS:
1. Transmitter unit
2. Receiver unit
3. Fiber Optic Cable
4. Multimeters
THEORY:
The light emitting diode is a PN junction device, which emits light when forward biased
by a phenomenon call electro luminescence. In all semi conductor PN junction, some of the
energy will be radiated as heat and some in the form of photons.
In silicon and germanium, greater percentage of energy is given out in the form of heat
and Gallium phosphide (GaP) or Gallium Arsenic Phosphide (GaAsP). The number of photons of
light energy emitted is significant to create a visible light source. Here the charge carrier
combination takes place when electrons from the n-side ions at the junction combine with the
holes on P- side.
The characteristic of LED are observed by the use of photo diode. LED emits the light is
observed by passing the light through fiber optic cable to the photo diode.
PROCEDURE:
1. Connect one end of cable 1M to the FO LED 1(660nm) port and the other end to the FO
PIN (power meter).
2. Switch ON the power supply.
3. Adjust the potentiometer, so that the power meter reads -15.0dBm.
4. Connect the DMM at terminal provided at FO LED1 and measure voltage in mV
5. Adjust the potentiometer to the extreme anticlockwise position to reduce If1 to 0.
6. Slowly turn the potentiometer clockwise to increase If1. The power meter should read -
30.0dB approximately. From here vary the port P0 in suitable steps and note the and note
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MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
OBSERVATIONS:
For LED1:
For LED2:
IF1 = 660nm LED Forward Current
IF2 = 850nm LED Forward Current
7. the power meter readings, record up to extreme clockwise and note down position and
note down the values.
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 34
S. No. V01(V) IF1 = V01/100 (mA) P0 (dB) m
S. No. V01(V) IF1 = V01/100 (mA) P0 (dB) m Corrected P0
(dB)m
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
8. Repeat the same procedure for FO LED2 and tabulate the readings.
RESULT:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 35
dmm1Set for Im Vs Po measurement
LASER ACCSet PO
FO pin
CablePmmaV0/ Gnd
TX UnitRX Unit
dmm2
Set for P0 Vs If measurement
LASER
ACC
Set PO
FO pin
CablePmma
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM:
ACC MODE
APC mode
OBSERVATIONS:
PO VS IF
S.No Vo(mV) If=(V0/100k)µA Vout (mV) P0(dBm)=(Vout/10)dB
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 36
dmm1
V0/ Gnd
TX UnitRX Unit
dmm2
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT: DATE:
CHARACTERISTICS OF LASER DIODE
AIM: To study the
1. Optical Power (P0) of a laser diode Vs. Laser diode forward current (If). i.e., study of
ACC Mode
2. Monitor photo diode current (Im) vs. laser optical power output (P0) i.e., study of APC
mode
APPARATUS:
1. Transmitter Unit
2. Receiver Unit
3. Fiber optic cable
4. Multimeters
THEORY:
Laser diode is a laser where the active medium is a semiconductor similar to that of LED.
The most common type of laser diode is formed from PN junction and powered by injecting
electric current.
Laser diode is formed by doping a very thin layer on the surface of a crystal wafer. The
crystal is doped to produce an n- type region one above the other, resulting in a PN junction or
diode.
Laser diodes are widely used in telecommunications as easily modulated and easily
coupled light sources for fiber optic communication. Another common use of laser diodes is in
barcode readers. Infra red and red laser diodes are commonly used in CD-players, CD-ROMs,
DVD technology. Violet lasers are used in HD DVD and blur ray technology.
High power laser diodes are used in industrial applications such as heat treating, cladding
and for other lasers such as “Diode pumped solid state lasers”.
ACC MODE:
ACC stands for automatic gain control.
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 37
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
OBSERVATIONS:
S.No Vm(mV) Im=(V0/100k)µA Vout(mV) P0(dBm)=(Vout/10)dB
MODEL GRAPHS:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 38
Im
ΜA
P0(dB)
ACC MODE:- APC MODE:-
P0(dB)
If
ΜA
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
In the ACC mode the feedback to the LASER driver is derived from the load current
If .here V0 tracks Vref. this may not ensures constant optical power for a given Vref, in LASER
threshold occurs due to change in temperature & ageing.
APC mode :
APC Stands for Automatic Power Control
In APC mode circuit derives its feedback from the monitor photo current which is proportional to
p0here Vm tracks Vref we get a constant optical power output irrespective of variations in
temperature and ageing.
PROCEDURE:
P0 Vs If experiment:
1. Connect the 2-meter PMMA FO cable to TX unit of LT -2023 and Couple the LASER
light to the power meter on the RX unit as shown. Select ACC mode of operations.
2. Set DMMI to the 2000mV range and on the RX side connect to the terminals marked P0
to it. the power meter is now ready for use.P0= Vout/10dBm
3. Set DMM2 to the 2000mV ranges and connect it between V0 and ground on the
transmitter unit
4. Adjust the set Po on the transmitter unit to the extreme anti clock wise position to reduce
it to 0. The power meter readings normally are below – 40dBm or out of range.
5. Slowly turn the set Po knob clockwise to increase If and Po. Note If and P0 readings. Take
closer reading prior to and above the laser threshold.
6. Plot the graph P0 Vs If on a semi log graph sheet. Determine the slopes prior to lasing
and after lasing. Record the laser threshold current.
Im VS P0 EXPERIMENT:
1. Connect the 2-meter PMMA cable transmitter unit of lT 2023 and couple the laser light
to the power meter as shown. Select APC mode of operation.
2. Set the DMMI to the 2000mV ranges. On the receiver unit, connect the Po terminals to
it. Turn it on. The power meter is now ready for use.
P0=(reading )/10dBm
3. Set the DMM2 to the 200 mV ranges and connect it between the V0 wire (Vm) and
ground on the TX unit.
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 39
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
4. Adjust the set P0 knob to the extreme anticlockwise position to reduce Im to the minimum
value. There will be a negligible offset voltage.
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 40
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
5. Change P0 in suitable steps and note the Vm reading. Record up to the extreme clockwise
position.
RESULT:
BLOCK DIAGRAM:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 41
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
OBSERVATIONS:
Gain characteristics:
Vin(V) Vout (V) Gain(VOut/Vin)
EXPT: DATE:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 42
VIN
FOPIN
CH1CH2
Vout
Vout
FG TX UNIT LASER RX UNIT
P0
CRO
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
INTENSITY MODULATION OF LASER OUTPUT THROUGH AN OPTICAL FIBER
AIM: To study following characteristics of a linear intensity modulation
Laser and fiber optic system
1. Gain Characteristics
2. Frequency Response
APPARATUS:
1. Transmitter Laser Kit
2. Laser Receiver Unit
3. FO Cable (PMMA)
4. CRO
5. Function Generator
THEORY:
Fiber optic communications is a method of transmitting information from one place to
another by sending pulses of light through an optical fiber. The light forms an electro magnetic
carrier wave that is modulated to carry information. First it was developed in 1970’s. fiber optic
communication system have revolutionized the telecommunications industry and have played a
major role in the advent of information age. Because of its advantages over electrical
transmission, optical fibers have largely replaced copper wire communications in case networks
in the developed world.
Optical fiber is used by many telephone communication companies to transmit telephone
signals, internet communication, cable TV signals
PROCEDURE:
Gain characteristics of a linear intensity modulation system:
1. Connect one end of PMMA cable to the LASER probe on the TX unit. The other end is
first connected to the FO pin (on Rx set) to the carrier power level of the laser. Then it is
removed and given to the FO (RX unit) to study the response of the system
Input Voltage (Vi) = volts
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 43
Vin (V)
VOUT (V)
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
Frequency (Hz) Output Voltage,Vo(V) Gain = 20log (VO/Vi)dB
MODEL GRAPH:
Gain Characteristics:
Frequency Response Characteristics:
2. Set DMM to 200mV range, connect it to PO. The power meter is now ready for the use.
P0=reading/10dBm.
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 44
Frequency (Hz)
Gain (dB)
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
3. ON the TX unit, connect Vin to the function generator (10 Hz to 500KHz) sine wave O/P,
10mv to 200mV O/P. Give the function generator O/P to CH1
4. On the RX unit, connect VOUT to CH2 of dual trace oscilloscope
5. Plug the AC mains for both systems
6. With PMMA FO cable connected to the power meter adjust the set PO knob to set the
optical power meter and connect the FO PT.
7. Set the signal frequency and amplitude to 2 KHz and 100mV respectively. Observe the
transmitted received signals on the oscilloscope. Set Rin suitably to get VOUT =VIN i.e.,
unity gain. Next vary Vin in suitable values from 100mV to 1000mV VP-P and note down
the values of VOUT
Frequency Response:
1. Repeat the above procedure from 1 to 6.
2. Set the amplitude to 100 mV and adjust Rin, so that maximum o/p observed in the
oscilloscope i.e., maximum gain.
3. Vary the function generator from 10KHz to 500KHz & note the values of VOUT
RESULT:
CIRCUIT DIAGRAM:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 45
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
OBSERVATIONS:
OBSERVATIONS:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 46
S. No. LENGTH(mm) WIDTH(mm) N.A
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT: DATE:
MEASUREMENT OF NA
AIM: To measure the numerical aperture (NA) of the fiber
APPARATUS:
1. Fiber optic analog transmitter and receiver
2. Patch chords.
3. Fiber optic links 1m and 5 m length.
4. Inline SMA Adapter.
5. Mandrel.
THEORY:
In optics, the numerical aperture (NA) of an optical system is dimensionless number
that characterizes the ranges of angles over which the system can accept or emit light such that the
NA of a beam is constant as the beam goes from one material to another material provided there
is no optical power at the interface. The exact definition of term varies slightly between different
areas of optics.
In most areas of optics, especially in microscopes the numerical aperture of an optical
system such as an objective lens is defined by
NA= n sin θ
Where ‘n’ is the refractive index of the medium in which the lens is working (n=1 for air and
n=1.33for pure water)
‘θ’ is the half angle of the maximum cone of light that can enter or exit the lens.
PROCEDURE:
1. Connect one end of fiber cable to the output socket of transmitter FO LED1 and the
other end to the numerical aperture measurement. Hold of white screen facing the fiber
such that its cut face is perpendicular to axis of fiber
2. Hold of white screen with 4 concentric circles (10, 15, 20,25mm diameter) vertically at
suitable distance to make the red spot from the fiber coincide with 10mm circle
4. Record the distance f screen from the fiber end and note down the diameter w of the
spot.
5. Compute the numerical aperture from formulae given below
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 47
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 48
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
6. Vary the distance in screen and fiber optic cable and make it coincide with one of the
concentric circles. Note its distance.
7. Tabulate the various distances and diameter of the circle made on the white screen and
compute the numerical aperture from formulae given below
RESULT:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 49
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
CIRCUIT DIAGRAM :
OBSERVATIONS:
For FO led1 (660nm)
S.No 1 m cable P01
(dBm)
2 m cable P02 (dBm)
5 m cable P03 (dBm)
Loss in cable -1
Pin1-P01
(dBm)
Loss in cable -2
Pin2-P02 (dBm)
Loss in cable - 3
P03-P01 (dBm)
Loss in 4 meters fiber
P03-P01 (dBm)
loss per meter at 660nm
P02-P01 (dBm)
Pin1= max power in cable 1(1m)
Pin2 = max power in cable 2(2m)
Pin3 = max power in cable 3(5m)
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 50
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
EXPT NO: DATE:
MEASUREMENT OF LOSSES FOR FIBER OPTIC ANALOG LINK
AIM :
1. To study the various type of loss in optical fiber
2. To measure the bending losses in the optical fiber at wave length of 660nm. And 850 nm.
3. To Measure the propagation of attenuation Loss in optical fiber at wave length of 660nm.
And 850 nm.
APPARATUS :
1. Fiber Optic Analog Transmitter and receiver2. Patch chords3. Fiber optic links 1m and 5m length4. Inline SMA Adapter5. Mandrel
THEORY:
Attenuation in optical fiber is a result of number of effects. Measurement of attenuation in
two cables can also be computed loss per meter (dB). Spectral response of the fiber at two
wavelengths 660nm and 850nm can be obtained.
The optical power at a distance, L in an optical fiber is given by PL = Po 10(−£
10)b
where Po is
the launched power, £ is attenuation coefficient in decibels per unit length. The typical attenuation
coefficient value for the fiber under consideration is 0-3 dB per meter at wavelength of 660nm.
Loss is expressed in decibels 10 log (Po/Pf)
PROCEDURE:
1. Connect the circuit as mentioned below.
a. Connect one end of cable (1 meter) to the FOLED1 (660nm) and the other end to the
FO PIN.
b. Connect optical fiber cable securely after relieving all twists and strains on the fiber.
2. Switch ON the power supply.
3. Set the potentiometer PO to set the power meter to a suitable value, 15.0dbm. Note this as
PO1.
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 51
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
4. Wind one turn of the fiber cable on the mandrel or on the circular type material and note
the new reading of the power meter as PO2.
For FO LED2 (850nm)
S.No 1 m cable P01
(dBm)
2 m cable P02 (dBm)
5 m cable P03 (dBm)
Loss in cable -1
Pin1-P01
(dBm)
Loss in cable -2
Pin2-P02 (dBm)
Loss in cable - 3
P03-P01 (dBm)
Loss in 4 meters fiber
P03-P01 (dBm)
loss per meter at 660nm
P02-P01 (dBm)
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 52
MICROWAVE & OPTICAL COMMUNICATION LAB Dept. of ECE
5. Switch OFF the power supply.
6. Now the loss due to bending and strain on the plastic fiber is PO2-PO1dB.
7. Repeat the experiment for the LED of 850nm of wave length.
8. Now compare the bending loss in the optical fiber at 660nm and 850nm.
PRECAUTIONS:
1. Avoid loose connections
2. Reading obtained should be taken without parallax error
RESULT:
SRI SAI ADITYA INSTITUTE OF SCIENCE& TECHNOLOGY 53