mw lab final

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


LAB INTERNAL EVALUATION

S.No Name of the Experiment Date Remarks


Klystron Power Supply

Klystron Mount &Tube Supply

Isolator Frequency Meter

Variable Attenuator

Detector Mount

Milli Ammeter


CIRCUIT DIAGRAM:

OBSERVATIONS:Mode Repeller-

Voltage (V)Output Current (mA)

Frequency (GHz)

Power=i2R(µW)(assume R=1)

1

2

3



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.



MODEL GRAPH:


MODES OF KLYSTRON TUBE

Frequency (GHz)

Out put Power (ΜW)

Repeller Voltage (V)

Repeller Voltage (V)


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:


Gunn Power Supply

Gunn oscillator

Pin modulator

Frequency Meter Detector mount

mountMount

Micro ammeter


CIRCUIT DIAGRAM:

OBSERVATIONS:

Frequency of operation of gunn diode:

GUNN BIAS VOLTAGE(V) GUNN DIODE CURRENT(µA)



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



MODEL GRAPH:


VTH

Voltage ( V)

Current (µA) Threshold Voltage


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:



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:


Klystron Power

supply

Klystron mount tube Isolator Variable Attenuator

Frequency meter

Test Attenuator

VSWR Meter

Detector Mount


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


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:


Attenuation

(dB)



Micrometer Reading (mm)


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:


Directional Coupler

Matched termination

Detector Mount

Directional Coupler

Microwave Source

Isolator Frequency Meter

Variable Attenuator

Detector Mount

Matched termination

Detector Mount


CIRCUIT DIAGRAM:


1 2

3

2

31

VSWR meter

VSWR meter

VSWR meter

Port 1 Port 2

Port 3

Port 4


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


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)



FORMULAE:

DIRECTIVITY = P in- P12 (dB)

COUPLING FACTOR = Pin-P13 (dB)



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:


Klystronmount tube

Frequency meter

Tunable Probe

Variable attenuator

Slotted line carraige

Klystron Power Supply

VSWR meter

meterMeter

Matched load


CIRCUIT DIAGRAM:


Coaxial Cable

Short end load

K – band waveguide


EXPT NO: DATE:

MEASUREMENT OF VSWR

AIM: To determine the standing wave ratio and reflection coefficient.

APPARATUS:

1. Klystron Power supply

2. Klystron mount


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



|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) =



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:



CIRCUIT DIAGRAM:


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


EXPT NO: DATE:

IMPEDANCE AND FREQUENCY MESUREMENT

AIM: To measure the unknown impedance – using Smith Chart

APPARATUS:

1. Klystron Power supply

2. Klystron mount


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.



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

=



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:


2Matched termination

Detector Mount

Gunn supply

Gunn oscillator

Pin modulator

Frequency meter

3 – port Circulator

VS WR Meter

Variable Attenuator


CIRCUIT DIAGRAM:



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



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 =



RESULT:



CIRCUIT DIAGRAM:



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



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.


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


8. Repeat the same procedure for FO LED2 and tabulate the readings.

RESULT:


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


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


dmm1

V0/ Gnd

TX UnitRX Unit

dmm2


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.



OBSERVATIONS:

S.No Vm(mV) Im=(V0/100k)µA Vout(mV) P0(dBm)=(Vout/10)dB

MODEL GRAPHS:


Im

ΜA

P0(dB)

ACC MODE:- APC MODE:-

P0(dB)

If

ΜA


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.



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.



5. Change P0 in suitable steps and note the Vm reading. Record up to the extreme clockwise

position.

RESULT:

BLOCK DIAGRAM:



OBSERVATIONS:

Gain characteristics:

Vin(V) Vout (V) Gain(VOut/Vin)

EXPT: DATE:


VIN

FOPIN

CH1CH2

Vout

Vout

FG TX UNIT LASER RX UNIT

P0

CRO


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


Vin (V)

VOUT (V)


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.


Frequency (Hz)

Gain (dB)


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:



OBSERVATIONS:

OBSERVATIONS:


S. No. LENGTH(mm) WIDTH(mm) N.A


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



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:



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)



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.



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)



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:


mw lab final

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