oc lab manual

8/12/2019 Oc Lab Manual

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LAB HANDOUT

OPTICAL COMMUNICATIONS

Course Code: 09EC417

IV/IV B.Tech, I Semester

Team of Instructors

Dr. G .V. SUBBARAO (CC)

D. S. RAM KIRAN M. DIVYA

M.V.D PRASAD S. SUSRUTHA BABU

K.SONY

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

KL UNIVERSITY

VADDESWARAM, GUNTUR522 502 (A.P.) INDIA

2013-14


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INDEX

1.LABORATORY PROFILE 3

2.LAB EVALUATION 3

3.PROPOSED LIST OF EXPERIMENTS 4

4.AIM OF SELECTING THE BASIC EXPERIMENTS 4

5.LAB MANUAL FOR BASIC EXPERIMENTS 5

a. EXPERIMENT 1 5

b.EXPERIMENT 2 8

c. EXPERIMENT 3 17

6.LIST OF PROPOSED PROJECTS 22


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1.LABORATORY PROFILEName of the lab : OPTICAL COMMUNICATIONS

Course code : 09EC417

Number of Basic Experiments : 3

Number of Mini Projects : 1 out of proposed 20.

Team of Lab Instructors : Dr. G .V. SUBBARAO (CC)

D. S. RAM KIRAN

VARA KUMARI

M.V.D PRASADS. SUSRUTHA BABU

K.SONY

Team of lab technicians :Padmasri and Satyavathi

Number of student for work bench : 3

2.LAB EVALUATIONDistribution of Weightage

S.No Component Marks Type of exam and

Mode of assessment

Scheme of examination

1 Laboratory60

End Lab examination

(external evaluation)

60 marks are allotted for semester end

laboratory/drawing examination.

40

20 Internal evaluation Midterm Lab Tests in lab

experiments/drawing/Job works and

Record

15 Internal evaluation Continuous Viva Voce evaluation

5 Attendance.


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3.PROPOSED LIST OF EXPERIMENTS1. MEASUREMENT OF LOSSES WITH OPTICAL FIBER Page No

a. Propagation ... 5b. Bending. 7

2. STUDY OF CHARACTERISTICSa. Sources

i. LASER 8ii. LED 13

b.

Detectorsi. Photo transistor. 14

3. STUDY OF MODULATION SCHEMESa. Frequency modulation.. 17b. Pulse width modulation 19c. Pulse Position modulation.. 20

4. AIM OF SELECTING BASIC EXPERIMENTS1. From the first experiment the student can get exposure to different types of losses ahead

during transmission of information over optical fiber link.

2. From the second experiment the student can able to analyze the data transmission usingvarious intensity modulation techniques in optical fiber communications.

3.

From the third experiment the student can assess the dynamic characteristics of theSources and Detectors used in optical fiber communications.


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5.LAB MANUAL FOR BASIC EXPERIMENTSEXPERIMENT: 1

Date:

Measurement of Losses in Optical Transmission path

AIM: a. Measurement of fiber propagation loss.

c. Measurement of bending loss.APPARATUS:

1.Laser / LED

2.Source coupler

3.Fibre spool

4.Detector

5.Power measurement apparatus

THEORY:

Power Loss in dB = 10 log (P1/P2) dB

Where, P1 and P2 represent the input and output light power. The losses of optical power in

fibers are wavelength dependent. Therefore, light of different wavelengths launched into the

same fiber will suffer different amount of losses. Attenuation coefficient is expressed in dB/km

and is found by dividing the loss by the length of the fiber.

JUMPER DIAGRAM FOR CONNECTIONS


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a. PROPAGATION LOSS:PROCEDURE:

1. The optical power using a sinusoidal i/p voltage of 1V at 1kHz, is fed into a long lengthfiber using the experimental setup as shown in the diagram.

2. The optical power (P1) is then measured at the far end of the fiber using a detector andpower meter.

3. Replace the fiber with another one of different length and estimate the o/p power (P2) andcompute its dB value.

4. Measure the lengths of fibers (L1, L2).5. Obtain their power loss per unit length.

OBSERVATIONS:

S.No Length of fiber

(m)

Vin

(V)

Vout

(V)

Ploss=10 log(Vout/Vin)

(dB)

= Ploss/Length

(dB/m)

# Fora best quality fibres these losses are of the order of 1 dB/ km or less.

b. BENDING LOSSPROCEDURE:

1. The optical power using a sinusoidal i/p voltage of 1V at 1kHz, is fed into a long lengthfiber formed into a loop using the experimental setup as shown in the diagram.

2. The optical power (P1) is then measured at the far end of the fiber using a detector andpower meter.

3. Change the diameter of the loop and repeat the procedure for 3 to 4 diameters andmeasure the o/p power.

4. Compute bending loss corresponding to the curvature in each step and plot a graph.


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OBSERVATIONS:

S.No Diameter of fiber

loop (cm)

Vin

(V)

Vout

(V)

Ploss=10 log(Vout/Vin)

(dB)

Model graph


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EXPERIMENT: 2

Date:

LASER DIODE CHARACTERISTICS

AIM:

Measurement of VI Characteristics of Laser Diode

EQUIPMENT:

1. Fiber Link - E Kit .

2. Glass Fiber Cable with ST connector

3. Patch cords

4. Voltmeter

5. Ammeter

6. Power Supply

EQUIPMENT SET UP:

Connection diagram


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THEORY

In Optical Fiber communication system, Electrical signal is first converted into optical

signal with the help ofEIO conversion device such as LED or LASER DIODE here. After this

optical signal is transmitted through Optical Fiber, it is retrieved in its original electrical form

with the help OlEconversion device such as photo detector.

Different technologies employed in chip fabrication lead to significant variation in

parameters for the various laser diodes. All the laser diodes distinguish themselves in offering

high output power coupled into the important peak wavelength of emission, conversion

efficiency (usually specified in terms of power launched in optical Fiber peak wavelength of

emission, conversion efficiency (usually specified in terms of power launched in optical Fiber

for specified forward current) optical rise and fall times which put the limitation on operating

frequency, maximum forward current through laser diode and typical forward voltage across

laser diode.

An important feature of laser diodes is their ability to respond to direct, high-speed

modulation. In pulse drive operation, if the DC bias current, Ib, is less than the threshold

current, Ith, a time delay will result between the drive current pulse and the optical power

output pulse. Therefore, the DC bias current is normally set just above the threshold current to

obtain quick response.

Photo detectors usually comes in variety of forms photoconductive, photovoltaic, transistor

type output and diode type output. Here also characteristics to be taken into account are

response time of the detector, which puts the limitation on the operating frequency, wavelength

sensitivity and responsivity.

FORWARD CURRENT Vrs. FORWARD VOLTAGE:

The current-voltage properties of the GaAIAs semiconductor laser are similar to that of silicondiodes.

When a forward voltage is applied to the laser, current starts to pass at a certain

threshold voltage. This is called the threshold voltage. The threshold voltage of the GaAIAs

semiconductor laser is approx. 1 .2V, which is considerably higher than that of silicon diodes

(approx. O.6V) in general. Since the reverse breakdown voltage is far lower (absolute maximum


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rating = 2V) than that of silicon diodes (more than 30V), care must be taken not to apply a

reverse voltage exceeding this maximum rating. FIG. 2.1 compares forward current and forward

voltage for different temperatures. The forward voltage of the GaAIAs semiconductor laser has

a temperature coefficient of approx.1.5 mV/oC (MAX). Forward voltage drops by approx. 75

mV over a 50C temperature variation.

BEFORE SWITCHING ON:

Before powering up LlNK-E ensure that the knobs to control the DC bias current to the Laser

Diode Transmitter are turned fully anti-clockwise.

TABULAR FORM:

FREQUENCY 1MHZ -1V1310Nm

S.NO. I(mA) V(Volt)

1 0

2 0.1

3 0.5

4 1

5 2

6 3

7 4

8 5

9 10

10 15

VI CHARACTERISTICS OF LASER DIODE

MODEL GRAPH:


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PROCEDURE:

FORWARD CURRENT VS. FORWARD VOLTAGE

1. Confirm that the power switch is in OFF position and then connect it to the kit.2. Make the jumper settings and connections as shown in the block diagram FIG.2.5.3. Insert the jumper connecting wires (provided along with the kit) in jumper JP1, JP2 and JP3

at positions shown in the diagram.

4. Connect the ammeter and voltmeter with the jumper wires connected to JP2 and JP3 withjumper at R16 as shown in the block diagram.

5. Keep switch SW1 in ANALOG position.6. Keep the potentiometer P5 in anti-clockwise rotation. It is used to control intensity of laser

diode.7. Connect external signal generator to ANALOG IN post of Analog buffer and apply sine

wave frequency of 1 MHz, 1V p-p signal precisely.

8. Then connect ANALOG OUT post to ANALOG IN post of transmitter.9. Then Switch on the power supply. To get the IV characteristics of Laser diode, rotate P5

lowly and measure forward current and corresponding forward voltage at JP2 and JP3


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respectively. Take number of such readings for various current values and plot IV

characteristics graph (FIG. 2.8) for the Laser diode.

BEFORE SWITCHING OFF:

When the experimental laboratory session has finished, first disable the waveform generator,

then reduce the current for Laser Diode Transmitters (e.g. turn anticlockwise), disconnect all the

fiber patch cords and replace their dust caps as well as those for the transmitter and the receiver.

Finally remove all of the patch cords and switch off the mains power at the rear of the unit.

RESULT: IV Characteristics of laser diode is obtained.


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EXPERIMENT:2

Date:

CHARACTERISTICS OF 850nm LEDs

AIM: To study the relationship between the LED dc forward current and the LED optical Power

output and to determine the linearity of the device at 660nm as well as 850nm.

APPARATUS:

1. Optical Fiber Analog Transmitter

2. Optical Fiber Analog Receiver

3. Optical Fiber

4. Probes

5. Digital Multimeters - 3


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THEORY:

To be useful in fiber transmission applications an LED must have a high radiance output, a fast

emission response time and a high quantum efficiency. Its radiance is a measure of the optical

power radiated into a unit solid angle per unit area of the emitting surface. High radiances are

necessary to couple sufficiently high optical power levels into a fiber. The emission response is

the time delay between the application of a current pulse and the onset of optical emission. The

quantum efficiency is related to the fraction of injected electron hole pairs that recombine

radiantly.

Jumper diagram for I-V characteristics

PROCEDURE:

1. Insert the jumper connecting wires in jumpers J 17 and J16 as shown in the above Figure.2. Connect the current meter and voltmeter with jumper wires connected to J17 and J 16 as

shown.

3. Keep the potentiometers Pr 10 in its maximum position and Pr 9 in its minimum position.Pr10 Controls the current flowing through LED, whereas Pr 9used to vary the amplitude of

the received signal at photo transistor.

I-V Characteristics of LED

4. Rotate Pr10 slowly and measure forward current and corresponding voltage. Take thenumber of readings for various current values and plot I-V Characteristics for LED.


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5. For each reading, find out the power by taking the product of I and V. Plot the graph ofoptical power output to forward current.

OBSERVATIONS:

For 660nm:

S.NO VOLTAGE (V) IE1(mA) PO

1

2

3

4

0.101

0.156

0.218

0.277

. .

MODEL GRAPH:

PHOTO TRANSISTOR DETECTOR CHARACTERISTICS:

4. Pr9 in its minimum position provides 100 in series of emitter and ground of phototransistor, hence Pr9 is kept in its minimum position.

5. Connect a fiber cable b/w LED(SFH756V) and photo transistor (SFH350V).6. Launch optical power onto fiber and measure output voltage at analog output terminal. Find

out the current flowing through photo transistor.

7. Repeat steps step 8 for various power values and plot the graph for the responsivity of phototransistor.


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Forward

Voltage of LED

VF (Volts)

Forward

current of LED

IF (mA)

Electrical power

Pi= VfIf (mW)

Optical

power

P0=1.15 Pi

V0 I R=(0.8

mA) P0 / 10

W

MODEL GRAPH:

PRECAUTIONS:

1. Optical fiber cable should be handled with care.

2. The readings should be taken without parallax errors.

3. Connect the optical fiber cable to the ports with minimum force applied, tightly so that no

path losses occur.

RESULT:

From this experiment we observe that the LEDs at 660nm and 850nm have a linear

response of P0versus IFin a limited region


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EXPERIMENT-3: STUDY OF MODULATION SCHEMES WITH OPTICAL FIBER

COMMUNICATION LINK

a. Frequency modulation.

b. Pulse width modulation.

c. Pulse amplitude modulation.

Aim: To study the circuit action of frequency modulation and demodulation over the fibre

cable link using 660 &950 nm LED.

APPARATUS:

1. Powersupply

2 Optical Fiber trainer kit,

3. 20Mhz Dual Trace Oscilloscope,

4. 1Mhz Function Generator,

5. 1mtr Cable,

6. 3mtr Cable,

7. Scale,

8. Calculator.

A. FREQUENCY MODULATION

THEORY

Frequency modulation conveys the information over message signal by varying its frequency

according amplitude .Here the modulating signal is a sinusoidal signal orany speech signal

.The frequency of the modulated signal varies with the amplitude of the carrier proportionally.

For transmission of the FM signal, we use of cables.


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Procedure:

1.Connect the fiber and arrange all the remaining as shown in the block diagram.

2.Slightly unscrew the cap of LEDSFH 756v Tx1 (660nm), do not remove the cap from the

connector. Once the cap is loosened, insert the fiber into the cap and ensure that the fiber

is properly fixed. Now tighten cap by screwing it back. Keep intensity pot P3 at minimum

position (fully anticlockwise).

3. Make connections and jumper settings as shown in figure. Connect the power supplycables with proper polarity to kit while connecting this ensure that the power supply is

OFF.

4. Select frequency range of about 1KHZ from function generator with the help of rangeselection switch sw1.Frequency can be varied with pot2.

5. Connect sineport of function generator section to FM input port of FM modulationsection.

6. Connect Fm out post section of FM modulator section to IN post of Fm modulator.


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7. Switch ON power supply and observe a signal on CRO at output port of analog bufferFM waveform from function generator ,could be observed.

8. Increase the time period of the CRO and you could obtain waveform as shown .keepyour voltage level to 0.5vpp.

9. The frequency deviation f can be calculated as follows. From CRO, evaluate fm andfm detecting the periods of respective sine waves.

10.Value of the modulation index mf is calculated by the mf= f/f, where f is the frequenyof modulating signal.

11.Connect other end of fibre to detector SFH250v in kit very carefully as per instruction instep1.

12.Observe output signal from detector at analog outport on CRO by adjusting intensity potp3.and you should get reproduction of original transmitted signal.

13.Observe demod.signal at fm demod. out pot and then observe output at filter out postwhich is named as output signal.

14.The fact that there is still same as high frequency ripple at output of FM.Demodulation block we use the lowpass filter block to overcome this problem.


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PRECAUTIONS:

1. Optical fiber cable should be handled with care.2. The readings should be taken without parallax errors.3. Connect the optical fiber cable to the ports with minimum force applied, tightly so that no

path losses occur.


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B. PULSE WIDTH MODULATION

PROCEDURE:

1. Connect the power supply to the transmitter and the receiver kit. While doing this, ensurethat the power supply is OFF.

2. Make the connection as per given in the block diagram shown below

3. Apply 1KHz,1V peak-to-peak voltage sine wave from function generator at PWM input4. Switch on the power supply and function generator.5. Observe the PWM waveform at PWM O/P.6. Vary the frequency of input sine wave and measured the variation in PWM O/P.7. Slightly unscrew the cap of IR LED SFH 450V (950nm) on the transmitter kit and insert the

fiber. After assuring that fiber is properly fixed, tighten the cap by screwing it back.

Similarly, connect the other end of fiber to detector SFH 250V on receiver kit.

8. Now connect the PWM output to amplifier AMP I/P and connect the AMP O/P totransmitter I/P.


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9. Short the both +9V by shorting link10. Observe the received signal at DETECTOR O/P in receiver kit. Adjust the gain control pot

P1 to obtain the same amplitude as the transmitted signal.

11. Connect the DETECTOR O/P to the input of pulse amplitude demodulator. Observed theoriginal sine wave at PWM O/P.


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C. PULSE POSITION MODULATION

PROCEDURE:

1. Connect the power supply to the transmitter and the receiver kit. While doing this, ensurethat the power supply is OFF.

2. Make the connection as per given in the block diagram in fig 2.1

3. Apply 1KHz,1V peak-to-peak voltage sine wave from function generator at PPM input4. Switch on the power supply and function generator.5. Observe the PPM waveform at PPM O/P6. Vary the Amplitude of input sine wave and measured the variation in PPM O/P


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7. Slightly unscrew the cap of LED SFH 256V (660nm) on the transmitter kit and insert thefiber. After assuring that fiber is properly fixed, tighten the cap by screwing it back.

Similarly, connect the other end of fiber to detector SFH 250V on receiver kit.

8. Now connect the PPM output to amplifier AMP I/P and connect the AMP O/P to transmitterI/P.

9. Short the both +9V by shorting link10. Observe the received signal at detector O/P in receiver kit. Adjust the gain control pot P1 to

obtain the same amplitude as the transmitted signal.

11. Connect the detector O/P to the input of pulse amplitude demodulator.12. Observed the original sine wave at PPM O/P as shown below.


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RESOLVING STEPS FOR THE PROPOSED PROJECTS

1. FIBER OPTIC LINK DESIGN.a. Power estimation at the source.b. Measure the sensitivity of the receiverc. Estimate the power loss with fiber.d. Estimate the total link loss and realize it.e. Design the link with estimations obtained from the above steps.

2. FIBER BASED VOICE/DATA COMMUNICATIONS.a. Identifying requirement at various levels of designing the link.b.

Voice/data to analog voltage conversion

c. Modulation of source with the data and launching power onto fiber.d. Extraction of power at the receiver using fiber link.e. Demodulation of the information at the second end.

3. OPTICAL COMMUNICATIONS FOR DEVICE CONTROLa. Identifying requirement at various levels of designing the link.b. Design interface for connecting a stepper motor at the detector end.c. Generate PWM to reflect the required speed.d. Design a PWM generating fiber link and excite it.e. Study various factors influencing motor speed and design.

4. IR REMOTE CONTROL (SINGLE OBJECT / MULTIPLE OBJECTS).a. Design a source to generate coding signal corresponding to a device.b. Design corresponding detector circuit within the device to respond.c. Activate them and test.d. Study distance, direction and attenuation for various cases.

5. DISTANCE MEASUREMENT USING CHIRP BASED STIMULATIONa. Generate chirp signal using FM modulator.b. Design a detector circuit for proper reception.c. Launch the generated chirp signal onto fiber and study spectral variations with

fiber length at the fiber end.


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d. Record the data using digital CRO and cross correlate the data.e. Estimate the time delay between auto correlation of generated signal and cross

correlated signal for fiber and free space gaps.

f. Estimate the distance.6. ESTIMATION OF ATTENUATION USING PULSE COMPRESSION.

a. Generate chirp signal using FM modulator.b. Design a detector circuit for proper reception.c. Launch the generated chirp signal onto fiber and study spectral variations with

fiber length at the fiber end.

d. Record the data using digital CRO and cross correlate the data.e. Estimate the correlation coefficient for various lengths of the fiber and bring a

relation for this method. Compare it with OTDR.

7. ESTIMATION SPECTRAL DISTORTION IN OPTICAL FIBERTRANSMISSION.

a. Generate various signals using FM modulator and study their spectraldistributions.

b. Launch them onto fiber and compare the spectral variations between i/p and o/psignals.

c. Repeat them for various fiber lengths.8. DESITY OF FLUID USING OPTICAL COMMUNICATION

a. Construct a fiber link putting an empty glass tube in its transmitting path.b. Study of attenuation property of the link by pouring a liquid of interest and

measure the reading of receiver.

c. Do the same for variety of liquids and calibrate the apparatus.d. Measure the unknown density of any liquid.

9. EVENT COUNTER/ SPEEDO METER DESIGN USING OPTICAL METHODS.a. Generate electro-optic equivalent of fiber using Simulink.b. Study of attenuation and spectral distortion for various lengths of fiberc. Estimate the time delay between auto correlation of generated signal and cross

correlated signal for fiber and free space gaps.

d. Estimate the distance.


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10.SPECTRAL RESPONSE OF OPTICAL FILTERS.a. Generate polychromatic radiation from source.b. Insert various filters in the path of propagation of light (b/w source and detector).c. Estimate intensity distribution at the receiver end and decide.d. Decide the photo response range of the detector.e. Study various possible detectors ranges and characteristics.

11.VELOCITY MEASUREMENT OF FLUIDS (VELOCIMETRY).a. Sending the fluid through a transparent tube and measure the velocity.b. Designing link for estimation of intensity variation using fiber link.c.

Testing it for various speeds of fluid.

d. Calibration and bringing relation b/w intensity variation and speed.12. MAXIMUM DIGITAL DATA RATE ESTIMATION USING EYE DIAGRAM.

a. Design of digital link.b. Transmitting pulse train through the link and detection.c. Generation of eye diagram and estimating its opening.d. Obtaining optimum data rate from maximum opening of Eye pattern.

13.OBTAIN THE GAIN FLATTENING USING SERIES EDFAa. Design the series EDFAb. Increase the no of i/p channelsc. Increase the transmission capacityd. Modify Material Compositione. Obtain the gain flattening

14.EVALUATE CHARACTERISTICS OF MULTIMODE FIBER USINGOPTIWAVE.

a. Design the fiber for various core radiusb. Estimate the RI of core and claddingc. Obtain the fiber profiled. Measure the MFD and Zero dispersion slopee. Compare the dispersion


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15.OBTAIN THE GAIN FLATTENING USING PARALLEL EDFAa. Design the parallel EDFAb. Increase the no of i/p channelsc. Increase the transmission capacityd. Material Compositione. Obtain the Gain Flattening

16.COMPARE SINGLE MODE AND MULTIMODE OPTICAL FIBERS.a. Design the fibers for various core radiusb. Estimate the RI of core and claddingc. Obtain the fiber profiled. Measure the different lossese. Evaluate the dispersion

17.DESIGN THE BASIC OPTICAL FIBER COMPONENT MODEL USED FORTELECOMMUNICATIONS

a. Creating a modelb. design a layout using the componentc. measure the i/p and o/p efficiencyd. Obtain the Optical Spectrume. Estimate the parameters power, gain

18.EVALUATE CHARACTERISTICS OF SINGLE MODE FIBER USINGOPTIWAVE

a. Design the fiber for various core radiusb. Estimate the RI of core and claddingc. Obtain the fiber profiled. Measure the MFD and Zero dispersion slopee. Compare the dispersion

19. DERIVE THE COUPLING EFFICIENCY BETWEEN SINGLE MODE FIBERTO PHOTONICS CRYSTAL FIBER USING FDTD METHOD.

a. Design a single and photonic crystal fiberb. Obtain the fiber profilesc. Evaluate the optical spectrum of the fibers


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d. Obtain the layout comprising the componentse. Evaluate the coupling Efficiency

20.EVALUATE THE GROUP DELAY, EFFECTIVE AREA FOR NEGATIVEDISPERSION FIBER

a. Design the fiber parameter for two different wavelengthsb. Estimate the Group Delay, Effective Areac. Compare for two wavelengthsd. Evaluate for 3 different core widthse. Obtain the fiber profile

After completion of the basic experiments in the lab lab one should develop a project eitherselected from the above list or on his/her own with the guidance of the instructor related to the

course. From this lab course one can analyze and able to develop various tasks related to optical

communications.

Course coordinator Administrative incharge Head of the Department

Dr. G V Subbarao Dr. M S G Prasad Dr. Habibullah Khan

oc lab manual

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