Optical Peri

8/10/2019 Optical Peri

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FIBER OPTIC COMMUNICATION LINKS

AIM:

To study the fiber optics analog and digital link.

APPARATUS REQUIRED:

1.Fiber optic trainer kit

2.Patch chords

3.CRO

THEORY:

Fiber optic links 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 modulates takes the input signal in electrical form and then transforms it

into optical 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:

ANALOG LINK:

1. Switch ON the power supply to the board.

2. Connect 1KHZ sine wave function generator output to the input of the emitter circuit.

3. Connect the emitter output to detector input by using fiber optic cable.

4. Connect the output of detector to input of amplifier.

5. Switch ON the power supply.

6. Observe the detected signal at post Analog out on oscilloscope.

7. To measure the analog bandwidth of the photo transistor vary the input signal frequency

and observe the detected signal at various frequencies.

8. Plot the detected signal against applied signal frequency and from the plot determines the

3dB down frequency.


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ANALOG LINK:

DIGITAL LINK:

MODEL GRAPH:

ANALOG LINK

INPUT WAVEFORM OUTPUT WAVEFORM


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DIGITAL LINK

INPUT WAVEFORM OUTPUT WAVEFORM

DIGITAL LINK

1. Connect the power supply to the board.

2. Connect 1KHZ sine wave function generator output to the digital buffer by means of

patch chords.

3. Connect the input to the emitter output to detector input by using fiber optic cable.

4. Switch ON the power supply.

5. Switch ON emitter a device to digital mode.

6. Observe the detector signal at post TTL OUT on oscilloscope.

7. To measure the digital bandwidth of the photo transistor vary the input signal frequency

and observe the detected signal at various frequencies.

8. Determine the frequency at which the detector stops recovering the signal. This determine

the maximum the bit rate on the digital link.

RESULT: Thus the 650nm fiber optic analog and digital link was studied.


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NUMERICAL APERTURE


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MEASUREMENT OF NUMERICAL APERTURE

AIM:

To measure the numerical aperture in optical fiber.

APPARATUS REQUIRED:

1. Fiber optic trainer kit

2. Patch chords3. Optical Fiber

4. Screen

THEORY:

Numerical aperture refers to the maximum light collecting capacity of the fiber at which the

light incident on the fiber end is totally internally reflected and is transmitted properly along the

fiber. The cone formed by the reflection of the angle along the axis of the fiber is the cone of

acceptance else it is refracted out of the fiber.

PROCEDURE:-

NUMERICAL APERTURE:

1. Connect the power supply board.

2. Connect the function generator of 1 KHz sine wave output to the input of emitter circuit.

3. Connect the one of fiber cable to the output sockets of emitter circuit.

4. Hold the white screen facing the fiber such that its cut face is perpendicular to the axis of true

fiber.

5. Hold the white screen with four concentric circles [10, 15, 20,25mm] vertically at a suitable

distance to make a red spot from the fiber coincide with 10mm circle.

6. Record the distance of the screen from the fibers end and note the diameter of spot.

7. Compute the numerical aperture using the formula N.A.= [r / (d2+ r2)]


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TABULATION:

NUMERICAL APERTURE:

Distance

D(mm)

Radius

r = [BC + DE] / 4N.A.= [r / (d2+ r2)]

8. Vary the distance between the fiber and the screen and making coincide with the circle.

9. Note down the circle distance.

10. Tabulate the various distances and diameter of the circles made on the white screens and

compute numerical aperture.

RESULT:

Thus the Numerical aperture and bending loss in optical fiber has been measured

and tabulated.


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DIAGRAM:

TABULATION:

ANGLE (DEGREES) OUTPUT POWER(db)


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MODE CHARECTERISTICS OF SINGLE MODE FIBER

AIM:

To select the mode field characteristics of fiber.

APPARATUS REQUIRED:

1. Single mode fiber

2. LD deliver module

3. XYZ positioner

4. Rotation stage with mounting post setup

5. Power meter with pin note adapter

THEORY:

For single mode fiber the geometric distribution of light in the propagating mode is

important when predicting the performance characteristics of these fibers. Thus, a fundamentalparameter of a single mode fiber is the mode field diameter. This parameter can be determined

from the mode-field distribution is analogous to the care diameter in multimode fibers, except

that in single mode fibers. Distribution of an Gaussian field,

E(r)=E(0)exp(-r2/W0

2)

Where r is the radius, E0 is the field at zero radius & W0 is the width of the electric field

distribution.

PROCEDURE:

1. Force the beam from the LD unit in SM fiber.

2. Insert the SM mode to a connecter holder mounted in XYZ positions &connect the other

end to the fiber mounted in XYZ positions.

3. Adjust the distance between the screen& the fiber to get the required image size is viewed

on the screen.


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4. Keep the LD driver potentiometer at minimum position & turn ON position.

5. Increase the LD power supply to the maximum position by turning the potentiometer in

the clockwise.

6. Adjust the collimating lens of the LED unit to get the bright spot on the screen.

7. Focus the output light from the fiber to the white screen, then rotate the filter till get the

Clear output

8. Sample image which is shown in fig.

RESULT:

Thus the mode characteristic of single mode fiber has been drawn.


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MEASUREMENT OF ATTENUATION, COUPLING AND BENDING LOSSES IN

OPTICAL FIBER

Aim:

The objective of this experiment is to measure the losses in an optical fiber communication link.

The experiment not only enables one to determine the propagation loss in the fiber, but also to

get a feel for bending and coupling losses.

Equipment Required:

1. OFT.

2. Two channel, 20MHZ Oscilloscope.

3. Function generator, 1HZ-10 MHZ.

4. Fiber alignment unit.

Theory:

PROCEDURE:

Attenuation at 850 nm:

1. Take the 1m fiber and setup and analog link using LED1 in the Optical Tx1 block and detector

PD1 in the Optical Rx1 block [850nm link]. Drive a 1V p-p 10 KHz sinusoidal signal with zerod.c. Observe the signal on the oscilloscope. Use the BNC I/Os for feeding in and observing

signals. Adjust the GAIN such that the received signal is not saturated. Do not disturb the levelof the signal at the function generator or the gain setting throughout the rest of the experiment.

2. Note the peak value of the signal received and designated it as V1. Replace the 1m fiber by the3m fiber between LED1 and PD1. Again note the peak value of the received signal and designateit as V3. If is the attenuation in the fiber and I1 and I3 are the exact length of the 1m and 3m

fibers in meters respectively, we have

Where is in nepers/m, and P1 and P3 are the received optical power with 1m and 3m fiber

respectively. Compute in dB/m for 850nm wavelength using =4.343where is in nepers/m.

Attenuation at 650nm:

3. Now setup the 650nm link using LED2, detector PD1 and the 1m fiber. Observe the signal onthe oscilloscope. Adjust the GAIN such that the received signal is not saturated. Note the peak

value of the 1m fiber with the 3m fiber between LED2 and PD1. Again without disturbing theGAIN, note the peak value of the received signal and designate it as V3. Compute in dB/m for

a 650nm wavelength using the expressions given Step2.

Bending Loss:


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Where is the attenuation constant in dB/m at 650nm and is the coupling loss in dB. Now

move the two fibers a bit apart in the Fiber Alignment Unit and note the decrease in the outputvoltage. Measure the coupling loss also.

6. With the two ends of the fiber are aligned as close as possible, place a drop of

glycerine/isopropylene through the hole provided in the Fiber Alignment unit so as to cover the

fiber ends. Note that the received signal now increases. Compute the coupling loss in thepresence of a index matching fluid like glycerin.

8. Now try aligning the two fibers without using the Fiber Alignment unit. Estimate the losses as

the two fibers are offset laterally and also when the two fibers are at an angle as shown Figure.

BLOCK DIAGRAM:

BENDING LOSS

BENDING LOSS:

Number in turns Output voltage(v)

RESULT:Thus various losses in an optical fiber communication link are measured.


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