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Microwave & Optical Communication Lab
Exp. No. :
Date :
MODE CHARACTERISTICS OF REFLEX KLYSTRON
AIM:
To study the mode characteristics of reflex klystron.
EQUIPMENTS:
1. Klystron power supply
2. Reflex Klystron with mount
3. Isolator
4. Variable Attenuator
5. Frequency meter
6. Waveguide-detector mount with detector
7. Micro ammeter, VSWR meter
8. Wave guide stand and accessories.
PROCEDURE:
a) Carrier Wave operation
1. Assemble the equipment as shown in figure with microammeter as indicating meter
2. Fire the Klystron correctly for CW operation with optimum beam voltage
3. Adjust the repeller voltage to maximum negative value and decrease it in steps of 1V and record o/p
power and frequency in table. The frequency is measured by tuning the frequency meter to have a dip in
the o/p each time. The frequency meter should be detuned each time while measuring power
4. Plot power/frequency versus repeller voltage to get mode curves-figure
5. Compute various parameters from the graph
Dept. Of Electronics & Communication 1
Microwave & Optical Communication Lab
b) Modulated source (square wave operation)
1. Assemble the equipment as shown in figure with VSWR meter as indicating meter
2. Set the mod-selector switch to AM-MOD position. Keep AM-MOD and AM- FRE, knob at the mid
position
3. Fire the Klystron correctly for square wave operation with optimum beam voltage
4. Adjust the modulation voltage and repeller voltage to obtain maximum reading in the VSWR meter and
read it on the power scale
5. Also adjust the klystron tuning plunger for a maximum in VSWR meter.
6. Repeat steps 3 to 6 of CW procedure
RESULT:
Dept. Of Electronics & Communication 2
Microwave & Optical Communication Lab
Figure: Mode Characteristics of reflex klystron
K Kly
Figure: Setup for study of Klystron tube
Dept. Of Electronics & Communication 3
Klystron Power Supply
Klystron Mount + Tube
Frequency meter
Variable attenuator
Isolator Detector mount
Micro ammeter
VSWR Meter
Microwave & Optical Communication Lab
Table: Mode Characteristics of Reflex Klystron
Sl no Repeller voltage,( V) Microammeter reading ( μ A ) Frequency,( GHz)
Dept. Of Electronics & Communication 4
Microwave & Optical Communication Lab
Exp. No. :
Date :
GUNN DIODE CHARACTERISTICS
AIM:
To study the Gunn oscillator as a source of microwave power and hence to study the
a) I-V characteristics
b) To find the threshold voltage.
EQUIPMENTS:
1 Gunn Oscillator
2 Gunn Oscillator power supply
3 PIN diode modulator
4 Isolator
5 Frequency meter
6 Attenuator
7 Detector with tunable mount.
PROCEDURE:
1. Set the equipment as shown in figure.
2. Set the Gunn oscillator micrometer tuning screw at suitable frequency (~9GHz). Adjust attenuator for
suitable power level
3. Change Gunn biasing in steps of 0.5V and record corresponding currents in the table (read current in the
panel meter of the Gunn power supply)
4. Draw the current voltage characteristic.
5. Set the Gunn bias voltage above Vo and with zero attenuation. Record power and frequency for this
Gunn diode biasing
6. Reduce the Gunn biasing in steps of 0.5V and record corresponding power and frequency
7. Plot power/frequency versus bias characteristics
Dept. Of Electronics & Communication 5
Microwave & Optical Communication Lab
8. With Gunn oscillator micrometer screw in the middle of its range, set Gunn biasing for maximum power
o/p and record in table this power and frequency of oscillation
9. Move micrometer screw to one extreme till power falls to a low but readable value
10. Move micrometer screw in the opposite direction in steps of 0.5mm and record in table, the power and
corresponding frequency till the screw reaches another extreme
11. Plot power versus frequency characteristics and frequency versus micrometer reading curve-the
calibration curve
RESULT:
Dept. Of Electronics & Communication 6
Microwave & Optical Communication Lab
Figure: I-V Characteristics of Gunn oscillator
K Kly
Figure: Setup for the study of Gunn Diode
Dept. Of Electronics & Communication 7
Vo V--
<----I
Power Supply
Gunn Oscillator
AttenuatorFr. Meter
PIN Modulator
Isolator
Micro Ammeter
Detector mount
V I
Microwave & Optical Communication Lab
Micrometer Reading = Frequency =
Table: I-V Characteristics
Sl no Bias Voltage (V) Current (mA) Threshold Voltage (V)
Dept. Of Electronics & Communication 8
Microwave & Optical Communication Lab
Exp. No. :
Date :
FREQUENCY AND WAVELENGTH MEASUREMENT
AIM:
To determine the frequency and wavelength in a rectangular waveguide and to verify the relation between λ0 ,
λg, and λc
EQUIPMENTS :
1. Klystron oscillaltor,
2. Isolator,
3. Frequency meter,
4. Variable attenuator,
5. Standing wave detector,
6. Movable short terminator
7. Klystron power supply
8. VSWR meter
PROCEDURE:
Frequency measurement:
1. Set up the microwave bench as shown in figure
2. Set variable attenuator at minimum position
3. Set VSWR meter at 40dB
4. Switch ON klystron power supply. Modulate with 1kHz square wave
5. Adjust the reflector voltage to get maximum deflection in the VSWR meter.
6. Maximize the deflection with tuning probe in the VSWR meter
7. Frequency measurement using frequency meter
8. Tune the frequency meter until a dip is observed in the VSWR meter. Also tune the frequency meter to
obtain minimum deflection. Note frequency directly from frequency meter.
Dept. Of Electronics & Communication 9
Microwave & Optical Communication Lab
Wavelength measurement:
9. Replace the termination with variable short. Detune the frequency meter.
10. Move the probe along slotted line. The deflection in the VSWR meter will vary.
11. Move probe to minimum deflection point.
12. Move the probe to next minimum position and record the probe position. Calculate guide wavelength as
twice the distance
13. Calculate guide wavelength (λg) as twice the distance between minimum positions.
14. λc is calculated as 2a, where a is the inner dimension of waveguide broader side
15. Calculate λO as
16. Calculate frequency using the expression f0= c/ λ0
RESULT
Dept. Of Electronics & Communication 10
Microwave & Optical Communication Lab
K Kly
Figure: Setup for frequency & wavelength measurements
Dept. Of Electronics & Communication 11
Klystron Power Supply
Klystron Mount + Tube
Frequency meter
Variable attenuator
Isolator Slotted Line
Termination
VSWR Meter
Microwave & Optical Communication Lab
Exp. No. :
Date :
ATTENUATOR CHARACTERISTICS
AIM:
To study the attenuator characteristics by
a) Measuring the insertion loss and
b) Plotting o/p power versus micrometer reading for the given variable attenuator.
EQUIPMENTS:
Standard microwave test bench and the given test attenuator.
PROCEDURE:
1. Assemble the equipment as shown in figure with VSWR as indicating meter
2. Fire the Klystron correctly for AM-MOD operation with optimum beam voltage
3. Adjust for maximum power o/p (~30dB). Note the o/p power in VSWR meter (P0)
4. Insert the test attenuator between frequency meter and detector mount without disturbing the bench.
5. Move the micrometer screw to fully released position. Note the o/p power in VSWR meter (P1).
Calculate the insertion loss as (P0-P1)
6. Move the micrometer screw in the opposite direction in steps of 0.5mm and note down the
corresponding power (P2) from the VSWR meter
7. Find out the attenuation (P1-P2) value for different micrometer readings and plot the graph
Dept. Of Electronics & Communication 12
Microwave & Optical Communication Lab
K Kly
Figure: Setup for studying attenuator characteristics
Table: Attenuator Characteristics
Input power P0 =
Sl no Micrometer reading (mm) o/p Power (dB) P2 P0-P2 (dB)
Dept. Of Electronics & Communication 13
Klystron Power Supply
Klystron Mount + Tube
Frequency meter
IsolatorAttenuator
TestAttenuator
Detector mount
VSWR Meter
Microwave & Optical Communication Lab
Calculation:
Frequency of operation =
Output power P1 =
Insertion loss = P0-P1 =
RESULT:
Dept. Of Electronics & Communication 14
Microwave & Optical Communication Lab
Exp. No. :
Date :
DIRECTIONAL COUPLER
AIM:
To measure the coupling factor, insertion loss and directivity
EQUIPMENTS:
Standard microwave test bench and the directional coupler under test and matched load.
PROCEDURE:
1. Assemble the equipment as shown in figure with VSWR as indicating meter
2. Fire the Klystron correctly for AM-MOD operation with optimum beam voltage
3. Adjust for maximum power o/p (~30dB). Note the o/p power in VSWR meter (Pi)
4. Insert the test directional coupler in the forward direction between frequency meter and detector
mount without disturbing the bench and connect the detector to the auxiliary arm with the main arm
o/p terminated in matched load
5. Note the auxiliary arm o/p power in VSWR meter (Pao), ie., the power coupled to the auxiliary arm.
Also calculate the coupling factor (C) as Pi-Pao.
6. Now carefully interchange the detector of the auxiliary line o/p and matched load of the main line
without disturbing the setup.
7. Note the main arm o/p power in VSWR meter (Po), and calculate insertion loss (L) as Pi-Po
8. Restore the original arrangement, with the exception that the directional coupler under test be in the
reverse direction.
9. Note the auxiliary arm o/p power in VSWR meter (Pd), it is assumed that Pi is same as before. The
directivity (D) is calculated as Pao-Pd
10. Compute the isolation (I) as Pi-Pd and also check I=C+D
RESULT
Dept. Of Electronics & Communication 15
Microwave & Optical Communication Lab
Figure: Directional coupler
K Kly
Figure: Setup for studying isolator & circulator
Calculation:
Frequency of operation =
Table: Directional coupler
Sl no Pi (db)Pao
(db)Po (db) Pd (db) C (dB) L (dB) D (dB)
I =
C+D
(dB)
1
2
Dept. Of Electronics & Communication 16
I/p, Port 1
O/pPort 2
Port 4
Port 3
Klystron Power Supply
Klystron Mount + Tube
Isolator+Attenuator+Fr. Meter
Directional Aux armMain armCoupler
Detector mount
VSWR Meter
Matchedload
Microwave & Optical Communication Lab
Exp. No. :
Date :
E-PLANE TEE & H-PLANE TEE
AIM:
To study the properties of E- and H-plane tee junctions and to determine isolations and coupling coefficients.
EQUIPMENTS:
Standard microwave test bench and the E- and H-plane tee junctions under test and matched load
PROCEDURE:
1. Assemble the equipment as shown in figure with VSWR as indicating meter
2. Fire the Klystron correctly for AM-MOD operation with optimum beam voltage
3. Adjust for maximum power o/p (~30dB). Note the o/p power in VSWR meter (Pi)
4. Insert the test E-plane tee junction between frequency meter and detector mount without disturbing the
bench. and connect the detector to one of the ports and terminate the other in a matched load.
5. Determine the isolation in decibels by noting the o/p level in the VSWR meter (db scale)
6. Interchange the position of the detector and matched load and determine the isolation in decibels by
noting the change in the o/p level
7. Repeat steps 4, 5 and 6 for other orientations of the tee as well as for H-plane tee also.
8. Calculate the coupling coefficient from C=10 (-α/20), where α is the attenuation. Substitute the isolation
calculated in each case as α and hence calculate coupling coefficient.
RESULT:
Dept. Of Electronics & Communication 17
Microwave & Optical Communication Lab
Dept. Of Electronics & Communication 18
1
2
3
H-Plane Tee
1
E-Plane Tee
2
3
Microwave & Optical Communication Lab
K Kly
Figure: Setup for studying E, H-plane
Calculation:
Frequency of operation =
Table: Insertion loss
i/p portPower at i/p
(dB)o/p port
Power at o/p
(dB)
Insertion
loss (dB)
Port 1 Port 2 I12 =
Port 3 I13 =
Port 2Port 1 I21 =
Port 3 I23 =
Port 3Port 1 I31 =
Port 2 I32 =
α1 = (I12+I21)/2 = α2 = (I23+I32)/2 = α3 = (I13+I31)/2
Hence the corresponding coupling factors are
C1 = C2 = C3 =
Dept. Of Electronics & Communication 19
Klystron Power Supply
Klystron Mount + Tube
Isolator+Attenuator+Fr. Meter
E-, H-planeTee
Detector mount
VSWR Meter
Matchedload
Microwave & Optical Communication Lab
Exp. No. :
Date :
LOW VSWR MEASUREMENT
AIM:
To study the method of measuring VSWR at the input of the component under test or unknown load when
VSWR < 10
EQUIPMENTS:
1. Standard microwave test bench
2. Slotted section slide screw tuner
3. Components under test.
PROCEDURE:
1. Assemble the equipment as shown in figure with microammeter as indicating meter
2. Terminate the load end with the given slide screw tuner followed by the matched load.
3. Fire the Klystron correctly for CW operation with optimum beam voltage
4. Tune the detector by adjusting the stub length for maximum meter deflection. Also set the slide screw
tuner for the desired VSWR
5. Set the probe position for maximum reading on microammeter. That is at voltage maximum of the
standing wave. Record the meter reading in the table
6. Move the probe along the slotted line and adjust it at minimum position, read and record in table.
7. Calculate the VSWR as (Imax/Imin)1/2.
8. Repeat the same for different components.
a. If a VSWR meter is used in place of microammeter, set the klystron for square wave modulation
and follow the following steps
9. Adjust the gain of the VSWR meter amplifier to give full scale deflection to read 1.00 on the VSWR
meter at the voltage maximum (step 5)
10. Move the probe along the slotted line and adjust it at minimum position, note the VSWR meter reading.
This gives the VSWR directly when the maximum is set for 1.00
Dept. Of Electronics & Communication 20
Microwave & Optical Communication Lab
Note 1: A slide screw tuner can be used between the slotted section and the component for generating any
desired VSWR between 1 and 10.
Note 2: A matched load has a VSWR close to unity. Hence to measure the VSWR of this matched load, the
slide screw tuner setup should be removed and only the matched load is connected. Then the measurement
procedure is same as before, but since the VSWR is close to unity, VSWR reading is taken after the VSWR
meter scale is set in the 1 to ∞ range. If the reading is less than 1.3, then it is changed over to EXPANDED
SWR scale when the slotted line probe is in the field minimum position. This reading gives the VSWR of the
matched load which will be close to unity ( do the experiment for
1) open ended wave guide 2) a blank flange 3) a terminated fixed attenuator
Note 3: Unloaded Q of a Cavity resonator. Connect the given test cavity in place of slide screw tuner and
matched load. Measure the VSWR for different frequencies and compute the Q of the cavity as explained in
appendix.
RESULT:
Dept. Of Electronics & Communication 21
Microwave & Optical Communication Lab
Standing wave patterns
K Kly
Figure: Setup for studying VSWR
Dept. Of Electronics & Communication 22
Klystron Power Supply
Klystron Mount + Tube
Isolator+Attenuator+ Fr. Meter
Slotted section
Slide MatchedScrew LoadTuner
VSWR MeterDetector Mount
Microwave & Optical Communication Lab
Calculation:
Table: Low VSWR measurement
Sl noMaximum reading
[I max (μA)]
Minimum reading
[I min (μA)] S=
[ In VSWR meter set the maximum reading as 1, hence minimum reading directly gives the VSWR]
Table: Low VSWR measurement ( VSWR meter)
Sl no S=
Dept. Of Electronics & Communication 23
Microwave & Optical Communication Lab
Exp. No. :
Date :
IMPEDANCE MEASUREMENT
AIM:
To measure the unknown impedance of the given device
EQUIPMENTS:
Standard microwave test bench, slotted section, iris backed with a matched load (a flat plate with round hole) as
unknown impedance and blank flange.
PROCEDURE:
1. Assemble the equipment as shown in figure with VSWR meter as indicating meter
2. Fire the Klystron correctly for AM-MOD operation with optimum beam voltage
3. Adjust for maximum power o/p (~30dB).
4. Terminate the slotted section with the blank flange and accurately measure the position of the voltage
minima (S1). (See figure) .Also calculate guide wave length.
5. Connect the device under test in place of blank flange and measure VSWR and the new positions of the
minima (X1). The VSWR can be used to calculate magnitude and the shift in position of the minima for
calculating the phase of the reflection coefficient. Note down lmin = S1-X1. Also determine the VSWR
value S and λg.
6. Compute the unknown load impedance of the given device from the lmin, S and λg analytically as
ZL=Zo (1-jStanβlmin)/ (S-jtanβlmin) or by using smith chart.
RESULT:
Dept. Of Electronics & Communication 24
Microwave & Optical Communication Lab
K Kly
Figure: Setup for Impedance measurement
Dept. Of Electronics & Communication 25
Klystron Power Supply
Klystron Mount + Tube
Isolator+Attenuator+Fr. Meter
Slotted section
Iris Matched Load
VSWR MeterDetector Mount
Microwave & Optical Communication Lab
Calculation:
Table: Impedace measurement
Sl. no S1 (cm) S2 (cm) X1(cm) λg (cm) lmin (cm)
Guide wave length =
VSWR, S =
Zmin =
β = 2π/λg =
ZL=Zo (1-jStanβlmin)/ (S-jtanβlmin) =
Dept. Of Electronics & Communication 26
Microwave & Optical Communication Lab
Exp. No. :
Date :
DIELECTRIC CONSTANT MEASUREMENT
AIM:
To study the two-point method for measuring dielectric constant of the given low loss solid dielectric (Teflon)
EQUIPMENTS:
Standard microwave test bench and slotted section samples of given dielectric and blank flange.
PROCEDURE
1. Assemble the equipment as shown in figure with microammeter as indicating meter. Terminate the load
end with the short circuit.
2. Fire the Klystron correctly for CW operation with optimum beam voltage
3. Tune the detector by adjusting the stub length for maximum meter deflection.
4. With no sample in the shorted wave guide, measure and record in the table the positions of standing
wave minima, starting from any arbitrary plane d =0 as shown in figure.Compute guide wavelength.
The position of the first minima is taken as d1min
5. Using frequency meter determine the frequency of operation and compute the free space wavelength
(verify the value by using λg and λc=2a)
6. Remove the short circuit, insert gently the dielectric sample and replace the short- circuit in such a
manner that it touches the end of the sample
7. Measure and record in table the position of the standing wave voltage minima from the same
reference plane as chosen in step 5. The position of the first minima (with dielectric is taken as d2min)
8. Find out the VSWR.
9. Measure and record waveguide dimensions. (For necessary theory refer appendix)
10. Calculate the dielectric constant (detailed description of the calculations are shown in appendix)
RESULT:
Dept. Of Electronics & Communication 27
Microwave & Optical Communication Lab
Figure: Setup for measuring the dielectric constant
Calculations:
Waveguide dimension , a= b=
Cut of wavelength λc (=2a) =
Frequency of operation =
Guide wave length λg (without dielectric) =
Guide wavelength λd (with dielectric) =
Table: Dielectric constant
Sl
noSample
Thickness
t1 (cm)
d 1min
(cm)
d2min
(cm)
tan β(δ1+t1))/
(β t1)
tan (βdt1)/
(βd t1)
Possible
values of X
X1 =
X2 =
X3=
X1 =
X2 =
X3=
X1 =
X2 =
X3=
Dept. Of Electronics & Communication 28
Klystron Power Supply
Klystron Mount + Tube
Isolator+Attenuator
Fr. Meter
Slotted section with
dielectric
Short circuit
MicroammeterDetector Mount
Microwave & Optical Communication Lab
Exp. No. :
Date :
HORN ANTENNA
AIM:
To study the E-plane and H-plane radiation pattern of a pyramidal horn antenna and compute
a) Beam width
b) Directional gain of the antenna.
EQUIPMENTS:
Standard microwave test bench, horn antennae, waveguide twist etc.
.
PROCEDURE:
1. Assemble the equipment as shown in figure with horns properly aligned and distance between antennas
equal to double of rmin > 2D2/λo . E vector must be parallel to the ground
2. Fire the Klystron correctly for CW operation with optimum beam voltage micrometer as indicating
meter
3. Adjust for maximum power o/p (~30dB). Record this power received in the table
4. Rotate the receiving antenna in steps of 10deg. On both the sides and enter it in the table
5. Plot the E plane radiation pattern and determine the half power beam width ӨE. compare it with the
theoretical value (ӨE.=53λo/b)
6. Repeat the procedure after replacing the waveguide twists with a straight wave guide and compute ӨH
(ӨH.=80λo/a)
7. Compute the directional gain of the antenna using G= 13326/ ӨE ӨH
8. Compare it with the theoretical value of G=2πab/ λo2
Dept. Of Electronics & Communication 29
Microwave & Optical Communication Lab
Figure: Setup for studying Horn antenna
Figure: Antenna radiation pattern, rectangular plot
Dept. Of Electronics & Communication 30
30 20 0 20 30 Angular displacement
0db
-3db
Microwave & Optical Communication Lab
Table: Antenna field pattern
Sl no E-plane setting H-plane setting
Angular
setting (deg)
o/p current (μA) Angular
setting
o/p current (μA)
Left right Left right
1 5 5
2 10 10
3 15 15
4 20 20
5 25 25
6 30 30
7 35 35
8 40 40
9 45 45
10 50 50
11 55 55
12 60 60
13 65 65
14 70 70
15 75 75
16 80 80
17 85 85
18 90 90
Calculations:
Waveguide dimension, a = b =
Frequency of operation =
Free space wavelength =
ӨE.=53λo/b =
ӨH.=80λo/a =
G= 13326/ ӨE ӨH =
G=2πab/ λo2 =
Dept. Of Electronics & Communication 31
Microwave & Optical Communication Lab
RESULT:
Dept. Of Electronics & Communication 32
Microwave & Optical Communication Lab
OPTICAL EXPERIMENTS
Dept. Of Electronics & Communication 33
Microwave & Optical Communication Lab
Exp. No. :
Date :
STUDY OF LOSSES IN OPTICAL FIBER
AIM:
To measure propagation loss and bending loss for two plastic fibers.
EQUIPMENTS:
1. Link-B kit with power supply,
2. Patch chords,
3. 20MHz dual channel oscilloscope,
4. 1MHz function generator,
5. 1&3m fiber cable.
PROCEDURE:
1. Make the connections. Connect the power supply cables with proper polarities to link-B kit. While
connecting this ensures that the power supply is OFF.
2. Keep the SW9 towards TX1 position for SFH756
3. Keep jumpers and SW8 positions as shown in fig.
4. Keep intensity control pot P2 towards minimum position.
5. Switch ON power supply.
6. Feed about 2Vp-p sinusoidal signal of 1 kHz from the function generator to the IN post of analog buffer.
7. Connect the output post OUT of analog buffer to the post TX IN of transmitter.
8. Slightly unscrew the cap of SFH756 V (660nm).Do not remove the cap from the connector. Once the cap
is loosened, insert the 1m fiber in to the cap. Now tighten the cap by unscrewing it back
9. Connect the other end of the fiber to the detector SFH350V (phototransistor detector) very carefully as per
the instructions above.
Dept. Of Electronics & Communication 34
Microwave & Optical Communication Lab
10. Observe the detected signal at post ANALOG OUT on oscilloscope. Adjust intensity control pot P2
optical power control potentiometer so that you receive signal of 2V p-p.
11. Measure the peak value of received signal at ANALOG OUT terminal. Let this value be V1.
12. Now replace 1m fiber with 3m fiber between same Led and detector. Do not disturb any settings. Again
take peak voltage reading and let it be V2.
13. If α is the attenuation of the fiber then we have P1/P2 =V1/V2= e[-α(L1+L2)] where
Where α = nepers/meter,
L1= Fiber length for V1
L2 = Fiber length for V2
This α is for peak wave length of 660nm
14. Switch OFF the power supply.
15. Keep SW9 towards TX1 position for SFH 756.
16. Set the jumpers to form simple analog link using LED SFH 450 V at 950nm and phototransistor SFH
350V with 1m fiber cable.
17. Switch ON power supply.
18. Repeat the same procedure as above for this link to get α at 950 nm and compare the α values.
MEASUREMENT OF BENDING LOSS:
1. Set up the 660 nm analog link using 1m fiber as per the above procedure.
2. Bend the fiber in a loop and measure the amplitude of received signal.
3. Keep reducing the diameter of bend to about 2 cm and take corresponding out voltage
readings (do not reduce loop diameter less than 1cm).
4. Plot the graph of received signal amplitude versus loop diameter repeat the procedure for second transmitter.
Dept. Of Electronics & Communication 35
Microwave & Optical Communication Lab
Figure : Jumper diagram for the study of losses
RESULT:
Dept. Of Electronics & Communication 36
Microwave & Optical Communication Lab
Exp. No. :
Date :
STUDY OF NUMERICAL APERTURE OF OPTICAL FIBER
AIM:
To measure the numerical aperture of optical fiber provided with the kit using 650nm wavelength LED and
find the V –number.
EQUIPMENTS:
1. FCL-01,
2. 1m fiber cable,
3. Ruler,
4. Power supply,
5. NA JIG.
PROCEDURE:
1. Make connections as shown in fig. Connect the power supply cables with proper polarity to FCL -01 kit.
While connecting this, ensure that power supply is OFF.
2. Slightly unscrew the cap of LED SFH 756V (660 nm).Do not remove the cap from the connector. Once
the cap is loosened, insert the fiber in to the cap. Now tighten the cap by screwing it back.
3. Keep the jumpers JP1, JP2 and JP4 on FCL 01 as shown in figure.
4. Keep the switch S2 in VI position.
5. Switch ON the power supply.
6. Insert the other end of the fiber in to the numerical aperture measurement JIG. Hold the white sheet facing
the fiber. Adjust the fiber such that its cut face is perpendicular to the axis of fiber.
7. Keep the distance of about 10mm between fiber tip and screen. Gently tighten the screw and thus fix the
fiber in the place.
8. Observe the bright red spot on the screen by varying intensity pot P3 and bias pot P4.
9. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN as indicated in
the figure
Dept. Of Electronics & Communication 37
Microwave & Optical Communication Lab
10. Mean radius is calculate using the formulae r = (MR+PN)/4
11. Find the numerical aperture of the fiber using the formulae
NA= sinθmax = r / d2+r2 where θmax is the maximum angle at which light
incident is properly transmitted through the fiber.
12. V- number can be calculated using the formulae:
V=2Π* NA *a / Λ
where a is the core radius of the fiber, NA is the Numerical aperture, Λ is the wavelength .
Dept. Of Electronics & Communication 38
Microwave & Optical Communication Lab
Figure : Jumper diagram for measurement of numerical aperture
Dept. Of Electronics & Communication 39
Microwave & Optical Communication Lab
RESULT:
Dept. Of Electronics & Communication 40
Microwave & Optical Communication Lab
Exp. No. :
Date :
STUDY OF CHARACTERISTICS OF FIBER OPTIC LED AND PHOTODETECTOR:
AIM:
To study the VI characteristics of fiber optic LED and plot the graph of forward current versus output
optical energy and also to study the photo detector response.
EQUIPMENTS:
FCL-01 & FCL-02, 1meter Fiber cable, Patch chords, Jumper to crocodile wires, Power Supply, Voltmeter,
Current meter, 20 MHz Dual Channel Oscilloscope.
PROCEDURE:
1. Make connections as shown in figure. Connect the power supply with proper polarity to FCL-01 & FCL-
02 Kits. While connecting this, ensure that the power supply is off.
2. Slightly unscrew the cap of LED SFH 756V (660 nm) .Don’t remove the cap from the connector. Once
the cap is loosened, insert the 1meter fiber into the cap. Now tighten the cap by screwing it back.
3. Slightly unscrew the cap of Photo detector SFH 250V. Don’t remove the cap from the connector. Once the
cap is loosened, insert the other end of the fiber into the cap. Now tighten the cap by screwing it back.
4. Keep the jumpers JP1, JP2, JP3 & JP4 on FCL-01 as shown in figure.
5. Keep jumpers JP1 &JP2 on FCL-02 as shown in figure.
6. Keep switch S2 in VI position on FCL-01
7. Connect voltmeter and current meter as per the polarities shown in figure.
8. Switch on the power supply.
9. Keep the potentiometer P3 in its maximum position.P3 is used to control current flowing through LED.
10. Keep potentiometer P4 in its fully clockwise rotation.P4 is used to control bias voltage of LED.
11. To get the VI characteristics of LED, rotate P3 slowly and measure the forward current and
corresponding forward voltage.
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12. For each reading taken above, find out power, which is the product of I and V. This is the electrical power
supplied to the LED. Data sheets for the Led specify optical power coupled into plastic fiber when
forward current was 10 mA as 200 µW. This means that the electrical power at 10 mA current is
converted into 200 µW of optical energy. Hence the efficiency of LED comes out to be approximately
1.15%.
13. With this efficiency assumed, find out optical power coupled into plastic optical fiber for each of the
reading. Plot the graph of forward current versus output optical power of the LED.
14. Similarly measure the current at the detector.
15. Plot the graph of receiver current versus output optical power of the LED.
16. Perform the above procedure again for all the combinations of the Transmitter & Receiver
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Microwave & Optical Communication Lab
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RESULT:
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OBSERVATION & CALCULATION
Vf= Forward voltage of LED SFH 756
If=Forward Current of LED SHF 756
Pi =V* I (Electrical Power)
Po=Pi* 1.15 % (Optical power of LED 756)
V=Output Voltage of SFH 250
I=Output Current of SFH 250
VI CHARACTERISTICS OF FIBER OPTIC LED & DETECTOR
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Vf(V) If (mA) Pi(mW) Po(µW) V (V) I (µA)