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EXPERIMENT 4: LOSSES IN OPTICAL FIBER

OBJECTIVE : At the end of this session, student should be able :

1.To measure the output power of signal

2. To calculate the attenuation for each bending angle

THEORY : Bending losses

A sharp bend in a fiber can cause significant losses as well as the possibility of

mechanical failure. It is easy to bend a short length of optic fiber to produce higher losses than a

whole kilometer of fiber in normal use. The ray shown in Figure 1 is safely outside of the critical

angle and is there for propagated correctly. Remember that the normal is always at right anglesto the surface of the core. Now, if the core bends, as in Figure 2, the normal will follow it and the

ray will now find itself on the wrong side of the critical angle and will escape.

Tight bends are therefore to be avoided but how tight is tight? The real answer to this is to

consult the specification of the fiber optic cable in use as the manufacturer will consider themechanical limitations as well as the bending losses.

Figure 1

figure 2

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EQUIPMENT:

1. Power Meter

2. Laser Light source

3. Fiber optic cable: 1310nm, 1550

4. Protector

PROCEDURE:

1. Measure the output power of light signal and calculate the attenuation for each bendingangle that is propagated via fiber optics. The output power will be measured by Power

Meter and Light Signal will be produced by Laser Light Source.

2. Use the fiber optic with wavelength, ;1310nm and ;1550nm for both experiment.

3. Use Protector Board for make and angle when you want to bend the cable.

i. Straight the cable (at 00)

Refer to the figure (a). The output power meter refer as reference power.(Press and hold the REF key for >2 seconds to set a new reference level

for the current wavelength. During the process, the REF sign will

flash twice on the screen and the buzzer sound is heard when the process

has been complete).

00

Figure (a)

ii. Bend the cable indifferent angle at one side.

Refer to figure (b). Bend the cable in step of 450 until 3150. Record

the output power of light signal at the power meter and calculate the

attenuation for each bending angle (output power meter reference

power).

Figure (b)

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POWER

METER

SINGLE MODE FIBER

OPTICLASER LIGHT

SOURCE

LASER

LIGHT

SOURCE

POWER

METER

2250

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iii. Bend the cable indifferent angle at both side.

Refer to figure (c). Bend the cable in step of 450 until 3150.

Record the output power of light signal at the power meter and

calculate the attenuation for each bending angle (output power meter

reference power).

Figure (c)

DATA AND OBSERVATION

Table for Result:

a)

Fiber Bending 00

Power Meter (dB)

Laser Light Source (dB)

Table (a)

b) Wave length : 1310

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LASER

LIGHT

SOURCEPOWER

METER

2250

2250

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Fiber

Bending 450 900 1350 1800 2250 2700 3150

Power

Meter

(dB)LaserLight

Source

(dB)

Table (b)

c) Wave length : 1550

Fiber

Bending 450 900 1350 1800 2250 2700 3150

Power

Meter(dB)

LaserLight

Source

(dB)

Table (c)

QUESTION AND ANSWER :

Calculate the attenuation for each bending angle using the formula below :

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Attenuation =

1. Calculate the attenuation for bending angle for table (b)

Fiber

Bending 450 1350 2250

Attenuation

FiberBending 2700 3150

Attenuation

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3. Calculate the attenuation for bending angle for table (c)

Fiber

Bending 450 1350 2250

Attenuation

FiberBending 2700 3150

Attenuation

3. Conclusion

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