optical communication practical

1

Department of Electronics and Communication Engineering

(LAB MANUAL)

Optical Communication Lab Course Code: MEEC - 520

Master of TechnologySecond Semester

(2013-14)

AL-FALAH UNIVERSITY

DHAUJ, FARIDABAD,HARYANA

Submitted by: Submitted To:

M.Tech (1st Semester-E&C) Roll No-MTE-13- Regn No13-AFED-

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OPTICAL COMMUNICATION SYSTEMS

INDEX

S.No. Experiments Date Remarks Signature of Faculty

1 To Study the Optical devices.

2 To Study Characteristics of Optical Fiber Transmitter

3To Study Characteristics of Optical Fiber LED.

4 To Set Up an Analog link using on Optical Fiber.

5 To Study Fiber Optical Voice Link

6 To Study Losses in Optical Fiber.

7 To Measure Na of Optical Fiber.

8 To Set Up Digital Link Using Optical Fiber

9 To Study Pulse Width Modulation & Demodulation.

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EXPERIMENT NO. :- 1

Aim :- To study optical devices.

Apparatus Required: - Experimental kit, FO-1304, connecting wires, optical Fiber.

Block Diagram:-

BASIC OPTICAL COMMUNICATION SYSTEM

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PPM & PWM

PWM

DEMODULATIONPPM TO PWM

CONVERTER

SIGNAL GENERATOR

AMPLIFIER

AUDIO

PRE-AMPLIFIER

AUDIO AMPLIFIER

TRANSMITTER

CLOCK CKT. LPF

RS

232

RS

232

TRANSMITTER RECEIVER

4

.

Theory: - The Purpose of fiber optics trainer kit is to provide the various fiber optics and digital communication techniques. The experimental kit FO-1304 consists of various blocks as in figure-1 showing its block diagram.

Signal Generators. Amplifiers. Transmitters. Pulse width modulation. Pulse position / Frequency modulation. Audio amplifier. TTL detector circuit. Photo diode detector circuit & Signal conducting unit. PWM and PPM demodulation. Plastic fiber optics transmitter diode. SFH 450v and SFH 756v. Plastic connector housing. Plastic fiber optics photo diode detector and housing SFH 450v &SFH 551v.

Signal Generator: - For generating sine wave, square wave, square wave signal generator is in built.

Amplifier:- For amplifying the signal generated by signal generator the amplifier input and output is provided in kit.

Transmitter:-The transmitter input port is provided to input the signal of amplifier or directly the signal of generator. Jumper setting is shown in the jumper setting diagram.

PWM &PPM Modulation:- The PWM &PPM modulated signal for output is provided by PWM/PPM output port.

TTL Detector circuit :- The TTL Detecting signal is given through TTL output.

Photo detector &Signal conditioning unit:-

The optical signal is detected using photo diode and then the signal is amplified signal conditioning unitPWM AND PPM demodulation: - this section of kit is the receiver section in which PPM\PWM

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Demodulation input are provide

PHOTODIODE detector and housing: - the two photodiodes at the receiving section Are SFH 250V and SFH 551V the plastic fiber optic photodiode detector is attached with plastic connects housing.

Plastic fiber transmitter diode and housing:- the two transmitter diodes SFH 450V and SFH 551V that are a housed in plastic connector housing .

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PRECAUTION:- 1 cutoff the ends of the cable with sharp knife to obtain a precise 90 angle for perfect matching.2 switch off the power supply while making connections.3 do not remove the cap of the connector, only slightly unscrew the cap and then adjust fiber.

RESULT:-The optical device is studied successfully.

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QUESTIONS (Experiment 1):

Q1. What is the frequency range for optical communication system?

……………………………………………………………………………………………………………………………………………………

Q2. Which optical communication device is used for optical reception?

……………………………………………………………………………………………………………………………………………….......

Q3. Describe Graded Index Multimode fiber?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q4. Which material is used for the fabrication of green LED?……………………………………………………………………………………………………………………………………………………..

Q5. What is the light coupling efficiency of LED to Optical Fiber?……………………………………………………………………………………………………………………………………………………

Q6. In what parameter the core and cladding material differ? …………………………………………………………………………………………………………………………………………………….

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EXPERIMENT NO: 2

AIM: - To study the fiber optical transmitter.

APPARATUS REQIRED: - Experimental kit

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THEORY:-The fiber optic transmitter are typically composed of a Signal Generator, Amplifier, Transmitter Section, Driver circuitry, Optical source

SIGNAL GENERATOR:- The signal generator provides the sine wave ,square wave signal as an analog signal input .It may be inbuilt.

AMPLIFIER:-The amplifier section is used to amplify the analog input signal such as sine wave or square wave signal.

TRANSMITTER:-This transmitter section provides the various jumper setting for the 2 combination of photo detector and transmitter diode as:- for SFH 450V and SFH 250V shown in figure and for SFH 750V and SFH 250V shown in figure. These jumpers are used for multiple power supply.

DRIVER CIRCUITRY: - For driving the transmitter diodes this section provides the driving circuitry. This is attached with the jumper in the transmitter section for multiple power supply.PRECAUTION:- 1. Cut-off ends of cable with sharp knife to obtain 90 angle.2. Switch off the power supply while making connections.3. Do not remove the cap of connectors, just slightly unscrew the cap and adjust fiber carefully.RESULT: - The optical transmitter is studied successfully.

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Q1. Name the optical modulation used for optical transmission?

……………………………………………………………………………………………………………………………………………………..

Q2. What is WDM?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q3. Give two advantages of WDM.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q4. Give two types of WDM.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q5. Why we need driver circuitry in optical transmission?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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EXPERIMENT NO: - 3

AIM: - To study the characteristic of fiber optic LED.

APPARATUS REQUIRED: - Experimental kit connecting wires.BLOCK DIAGRAM:

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THEORY: - In optical fiber commn. System, electrical signal is first converted in to optical signal. With the help of e/o conversion device as LED. After this optical signal is transmitted through optical fiber, it is retrieved in its original electrical form with the help of o/e conversion device as photo detector. Different technology employed in chip fabrication lead to significant variation in parameters for the various emitter diodes. All the emitters distinguish themselves in offering high output power coupled into the plastic fiber. Data sheets for LEDs usually specific electrical and optical characteristics, out of which are important peak wavelength of emissions, conversion efficiency

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optical rise and fall times which put the limitation on operating frequency, max forward current through LED and typical forward voltage across LED.

PROCEDURE:1. Slightly unscrew the cap of IR LED SFH 450 V from kit. Once the cap is loosened insert fiber

carefully, tighten the cap by screwing it back.2. Make the jumper setting as in figure.3. Connect the signal between the amp. Input and ground port in kit.4. Switch on the power supply and measure the variation in the current with the changing

voltages.5. Draw the characteristics of LED.

PRECAUTIONS:

1. Cut off the ends of the cable with sharp knife to obtain a precise 90 degree angle.2. Switch off the power supply while making the connections.3. Do not remove the cap completely, just unscrew it and adjust fiber carefully.

RESULT: Hence we have successfully studied LED characteristics.


1. What is the relation between input current and output optical power?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...

Q2. What is indirect band gap semiconductor?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q3. Name various LED driver circuit.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q4. The LED characteristic’s graph between ………………..&……………………….?

Q5. Name the different materials used for the fabrication of LED?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

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Experiment No.-4

To set up an analog link using optical fiber

AIM: To set up an analog link using optical fiber.

APPARATUS REQUIRED: Experimental kit- FO-1304, CRO, BNC connector, connecting wires, optical fiber.

BLOCK DIAGRAM:

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THEORY: Fiber optic links can be used for transmission of digital as well as analog link signals. Basically a fiber optic link contains 3 main elements-a transmitter, an optical fiber and a receiver.

The transmitter module takes the input signal in electrical form and then transforms it into optical (light) energy containing the same information. The optical fiber is the medium which carries this energy to the receiver. At the receiver light is converted back into electrical form with the same pattern as originally fed to the transmitter.

PROCEDURE:

1. Slightly unscrew the cap of IR LED SFH 450 V from kit. Once the cap is loosened insert the fiber into the cap and assure that the fiber is properly fixed, now tighten the cap by screwing it back.

2. Make the jumper connections as shown in jumper block diagram. Connect power supply cables with proper polarity to kit. While connecting this ensure that the power supply is off.

3. Connect the signal generator between the amp. Input and ground ports in kit or on board sine wave output to amp. Input to feed the analog signal.

4. .Keep the signal generator in sine wave mode and select the frequency of with amplitude of or if on board sine wave adjust voltage accordingly.

5. Switch on the power supply and signal generator if used.6. Check the output signal f amp. , it should be same as that of applied input signal.7. Now rotate the optical power control below power supply connector in kit as desired. This

ensures min. current flow through LED.8. Connect the other end of fiber to detector SFH 250V in kit very carefully as per the step 1.9. Observe the output signal from the detector output port on CRO by adjusting optical power

control and such that it reproduces same transmitted signal.

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PRECAUTIONS:


RESULT: The analog link using optical fiber is successfully set.


Q1. What is optical Analog modulation?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...

Q2. Is wireless optical link possible? How?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q3. Why optical fiber cable is preferred for establishing long distance communication?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q4. Name two optical communication impairments?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q5. Explain the cone of Acceptance.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q6. How communication is effected by the length of the fiber.

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………......

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EXPERIMENT NO:- 5

AIM: To set up fiber optic voice link.

APPARATUS REQUIRED: Experimental kit- FO-1304, CRO, BNC connectors (CRO probes) , connecting wires, optical fiber, 20 MHz dual channel oscilloscope, microphone, speaker set.

BLOCK DIAGRAM:

THEORY: Fiber optic link for voice signal can be easily generated as for simple analog signal. Basically a fiber optic link contains 3 main elements-a transmitter, an optical fiber and a receiver.

The transmitter module takes the input signal in electrical form and then transforms it into optical(light) energy containing the same information. The optical fiber is the medium which carries this energy to the receiver. At the receiver light is converted back into electrical form with the same pattern as originally fed to the transmitter.

Here the microphone is used to input the voice signal to electrical components and the speakers at Tx and are used to get the output of voice signal.

PROCEDURE:

1. Connect the microphone provided with the kit to the socket marked MICJACK in the audio pre amp. Section of kit.

2. Connect speakers provide with the kit to the source socket marked SPEAKERJACK in the audio amp. Section of kit.

3. Now in simple analog link, remove the signal generator output from amp. Input port and apply MIC output from MIC output port in the kit.

4. Similarly connect output of photo detector from post detector output to the post audio input.

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5. Adjust optical power control port and voice control to set up fiber optic audio link.

PRECAUTIONS:


RESULT: The voice link using optical fiber is successfully setup.


Q1. What is the frequency range of human voice?

…………………………………………………………………………………………………………………………………………………..

Q2. What is total internal reflection in optical fiber?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Q3. Name the different losses in optical fiber.

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q4. What is Pulse broadening?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q5. Different types of bending lose in optical fiber?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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EXPERIMENT NO: - 6

AIM: - To Study the losses in optical fiber

APPARTUS REQUIRED: - Experimental kit connecting wires, 20MHZ dual trace CRO fiber cable ,CRO probes BNC connector.

BLOCK DIAGRAM:

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THEORY: - Optical fiber is available in different variety of material .these material are usually selected by to king in to as count their absorption characteristics for different wavelength of the light. In case of optical fiber; since the signal is transmitted in the form of light which is completely different in nature as that of electrons, one has to consider the insertion of matter with the radiation to study the losses in fiber. Losses are introduced in fiber due to various reasons.

As light propagates from one end of fiber to reflected back or some other direction from the Impurity particular present in the material contributing to the loss of the signal at the other end of the fiber . In general, terms it’s known as propagation loss. Plastics fibers have higher loss of the order of 180 db/km. whenever the condition for angle of incidence of the incident light is isolated the loss are introduced due to refraction of light. This occurs when fiber is subjected to the bending lower the radius of curvature more is the loss. Another loss is due to the coupling of fiber at LED and photo detector ends.

PROCEDURE:-

1. Make jumper connections as shown in jumper block diag. connect the power supply cables with polarity kit .while connecting this; ensure that power supply is off.

2. Connect the signal generator between the AMP input and GND port or SINE WAVE output to AMP input to feed the analog signal to the preamplifier.

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3. Keep the signal generator in sine wave mode or adjust voltage level if on board SINEWAVE output is used ,keep switch above power connectors at upper position,

4. Switch ON the power supply and check the output signal of the preamplifier at the AMP output. It should be same as that of the applied input signal.

5. Now rotate the optical power control put to ensure minimum current flow through LED.6. Short the AMP o/p and TX o/p.7. Connect the other end of the fiber to detector SFH 250v very carefully as per step 1. 8. Observe the output signal from detector at AC output port on CRO. Adjust optical power control

to get the reproduction of the original transmitted signal. Also adjust the amplitude of received signal as that of the transmitted one. Mark this amplitude level as V1.

9. Now adjust the optical fiber without disturbing any of previous settings, measure the amplitude level at the receiver side again, this is less than the previous one. Mark this as V2.

10. If α is the attenuation of the fiber then we haveP1/P2=V1/V2=exp[-α(I1+I2)]Where α is Nepers/MeterI1 is fiber length for V1I2 is fiber length for V2This α is the wavelength of 950 nm. To get the α for 660nm wavelength proceed as follows.

11. Make use of SFH 756V and SFH 250V to perform this experiment.12. Make the jumper setting as shown in the jumper block diagram.13. Repeat steps 1 to 11 replacing SFH 450V by SFH 756V.

Compare the values of α and find out the wavelength which has less attenuation in fiber.

Measurement of bending losses:1. Repeat all the steps 1 to 9 as above.2. Bend the fiber in a loop. Measure the amplitude of the received signal.3. Keep reducing the diameter to about 2cm and take corresponding output voltage reading.4. Plot a graph of the received signal amplitude v/s the loop diameter.

PRECAUTIONS:


RESULT: The losses of fiber are studied carefully.

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Q1. What is Rayleigh’s scattering?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Q2. What is the reason for Mie scattering?

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Q3. What is material dispersion?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q4. What is wave guide dispersion?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q5. What are the causes of absorption?

…………………………………………………………………………………………………………………………………………………….

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EXPERIMENT NO -7

AIM: Measurement of Numerical aperture of fiber.

APPARATUS REQUIRED: Experimental kit fiber link FO-1304, fiber cable, fiber holding fixture, ruler.

BLOCK DIAGRAM:

THEORY: N.A. refers to the maximum angle at which the light on the fiber cable end is total internally reflected and is transmitted properly along the fiber. The cone formed by the rotation of this angle along the axis of the fiber is cone acceptance of the fiber. The light ray should strike the refracted out of fiber cone. By the relation of numerical aperture and refractive indices as –

Q max= sin-1 (n12-n22)1/2 =sin-1(NA)

This is the formula that relates the acceptance angle (Qmax) and NA of the fiber.

PROCEDURE:

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1. Slightly unscrew the cap of LED SFH 756V. Do not remove the cap from the connector. Once the cap is loosened, insert the fiber in to the cap and assure that fiber is properly fixed , Now tighten the cap by screwing it back.

2. Now short the jumper as shown in jumper block diagram. Remove jumper caps of JP7 and JP8.3. Connect the power cord to the kit and switch on power supply. Keep switch near power

connection at lower position.4. Apply square output signal to BUF input and short BUF output to transmitter input.5. Insert the other end of fiber to the NA measurement figure. Hold the white sheet facing the

fiber. Adjust the fiber such that its cut face is perpendicular to the axis of the fiber.6. Keep the distance of about 10mm between the fiber tip and the screen. Gently tighten the

screw and thus fix the fiber in the place.7. Now observe the illuminated circular path of the light on the screen.8. Measure exactly the distance d and also vertical and horizontal diameter MR and PN indicated in

figure.9. Mean radius is calculated using the formula

r= (MR+PN)/410. Find the NA of the fiber using the formula

NA= sin (Qmax) =r/(d2+r2)1/2 Where Qmax is the maximum angle at which the incident light is properly transmitted through the fiber.

PRECAUTIONS:


RESULT: numerical aperture is observed carefully.


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Q1. Describe numerical aperture?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q2. What is refractive index difference?

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Q3. What is critical angle?

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Q4. Give the relation between critical angle and cone of acceptance?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Q5. Describe Snell’s law.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...

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EXPERIMENT NO-8

AIM: To setup the digital link using the optical fiber.

APPARATUS REQUIRED: Experimental kit FO-1304, fiber cable, dual trace oscilloscope, CRO probes.

BLOCK DIARGRAM:

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THEORY:

Fiber optic link can be used for transmission of digital as well as analog signals. Basically a fiber optic link contains three main elements- a transmitter, an optical fiber and a receiver.

The transmitter module takes the input signal in electrical form and then transforms it into optical(light) energy containing the same information. The optical fiber is the medium which carries this energy to the receiver. At the receiver light is converted back into electrical form with the same pattern as originally fed to the transmitter.

The analog signal(the electrical signal) is in the form that has to be converted to digital so at transmitter ADC is used and at receiver DAC is used to convert the information from analog to digital and vice-versa.

PROCEDURE:

1. Slightly unscrew the cap of IR LED SFH 450V. Do not remove the cap from the connector.Once the cap is loosened ,insert the fiber in to the cap and assure that fiber is properly fixed , Now tighten the cap by screwing it back.

2. Now short the jumper as shown in jumper block diagram. 3. Connect the power supply to the main supply. Keep switch near power connection at lower

position.

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4. Give the TTL signal from the function generator between BUF output and GND terminal of the kit. It should be same as that of input signal.

5. Short BUF output and transmitter input ports with the help of shortening link provided.6. Connect the fiber to detector very carefully.7. Observe the signal on CRO at TTL output port. The transmitter and receiver signal are same

except of a slight delay in received signal.8. Repeat all the steps for SFH 756V and change the jumper setting as per jumper diagram.

PRECAUTIONS:


RESULT: The digital link using optical fiber is setup successfully.


Q1. What is BER?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Q2. What you mean by digital communication?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q3. Name the modulation schemes used in digital communication?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q4. Which modulation scheme is better for optical communication?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Q5. Define baud?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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EXPERIMENT NO -9

AIM: Study of pulse width modulation and demodulation using optical fiber.


BLOCK DIAGRAM:

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THEORY: PWM controls the variation of duty cycle of the square wave according to the input modulating signal. The amplitude variation of the modulating signal is reflected into on period variation of square wave. Hence it is also called as technique of V-T conversion.

The circuit consists of op-amp having unity gain, non-inverting amplifier as level shifter. When there is no signal, the output of the amplifier simply follows the voltage at inverting input terminal, with inverted polarity for the PWM part. Now put the input signal to non-inverting terminal over the regulating PWM. This consist of one fixed frequency oscillator whose frequency is decided by timing register Rt and capacitor Ct. the regulation is simply by formula-

F= 1.18/(Rt * Ct)

Where F is in kHz.

Rt in kΩ and Ct in µF.

In pulse width demodulation during the on time of PWM signal one counter is enabled. At the end of one time counter a particular count, which directly corresponds to the amplitude of input signal. Then this count is fed to a DAC. The output of DAC corresponds to the amplitude of the input signal. Thus train of varying pulse width gives varying current values and DAC gives output which is proportional to amplitude of input signal. Thus at the output we get the originally modulating signal.

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PROCEDURE:

1. Slightly unscrew the cap of LED SFH 756V. Do not remove the cap from the connector. Once the cap is loosened, insert the fiber in to the cap and assure that fiber is properly fixed , Now tighten the cap by screwing it back.

2. Connect the power supply to mains, keep it off.3. Make the jumper setting as in jumper block diagram.4. Connect the signal generator between PWM input and GND.5. Keep the signal generator in sine wave with given frequency and amplitude.6. Switch on power supply. Keep switch near power connector at lower position.7. Observe PWM signal at PWM output port. Vary the width of square wave but keep it low.8. Short the PWM output and BUF output to Tx input.9. Connect the fiber to detector SFH 551V with step 1.10. Connect the other end of fiber to detector SFH 551 carefully as per step 1.11. Observe the Rx signal over fiber at TTL output. It should be exactly similar to the signal available

at output port, short TTL output to DEMOD input (PWM).12. Vary the frequency of input signal and observe the demodulated sine wave at DEMOD signal

port.13. Short the DEMOD signal to filter and observe output of filter.

PRECAUTIONS:


RESULT: The PWM modulation and demodulation is studied successfully.

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Q1. What is PWM?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q2. Which parameter of pulse changes in PWM?

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Q3. Differentiate PWM and PPM.

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Q4. Differentiate WDM and PWM.

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Q5. Give two disadvantages of PWM.

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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EXPERIMENT NO.10

AIM: To study pulse position modulation and demodulation.


BLOCK DIAGRAM:

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THEORY: The position of TTL pulse is changed on time scale according to the variation of input modulating signal amplitude. In the PWM signal, the pulse duration is changing and this change the pulse duration causes for the delay of triggering. So the signal input modulating signal must be converted into the pulse width modulated form before applying to pulse modulator. The pulse positions are directly proportional to the instantaneous values of modulating signal.

In the pulse position demodulation the PPM signal is ORed with pulse generated by the rising edge of pulse width modulated signal. The output of the OR gate is fed to the CLK input of Flip-Flop. Thus flip flop act as a stable multivibrator giving out high output for the duration between rising edge of PWM signal and PPM signal. Now the PPM signal is exactly same as that of PWM signal, then it is demodulated using PWM demodulation as in earlier experiment.

PROCEDURE:

1. Slightly unscrew the cap of LED SFH 756V. Do not remove the cap from the connector.Once the cap is loosened ,insert the fiber in to the cap and assure that fiber is properly fixed , Now tighten the cap by screwing it back.

2. Connect the power supply to mains, keep it off.3. Make the jumper setting as in jumper block diagram.4. Connect the signal generator between PWM input and GND.5. Keep the signal generator in sine wave with given frequency and amplitude.6. Switch on power supply, observe PPM signal at PPM output port variation with shifted position

on time scale but the amplitude and width of pulses are same.7. Short the PPM output with BUF input and BUF output with Tx input.

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8. Connect the other end of fiber to detector SFH 551 carefully as per step 1.9. Observe the Rx signal over fiber at TTL output. It should be exactly similar to the signal available

at PPM output port.10. Connect this TTL output to the DEMOD output port to filter input(PPM).11. Vary the input frequency and observe demodulated signal at DEMOD output port. Connect

DEMOD output port to filter and observe output at filter output which is same as input signal.

PRECAUTIONS:


RESULT: PPM modulation and demodulation is studied successfully.

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optical communication practical