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University of Technology

 Laser and Optoelectronics Engineering Department

Optical Fiber Communication Lab. 2010-2011

Experiment No. (5)Bending Losses in Optical fiber

Experiment aim

To measure the bend loss in several samples of grade index multi mode

fiber as a function of bend radius.

Equipments

1.  Bend board

2.  62.5/125m ( ST-to-ST) optical fiber

3.  Reference light source

4.  Optical power meter

Bending losses 

Radiative losses occur whenever an optical fiber undergoes a bend

of finite radius of curvature. Fibers can be subject to two types of bend:

1-  Macroscopic bends having radii that are large compared to the fiber

diameter.

2-  Random microscopic bend of the fiber axis that can arise when the

fibers are incorporated into cables.

Let us examine large – curvature radiation losses, which are known as

macrobending losses. For slight bend the excess loss is extremely small

and is essentially unobservable. As the radius of curvature decrease, the

loss increases exponentially until at a certain critical radius the curvature

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University of Technology

 Laser and Optoelectronics Engineering Department

Optical Fiber Communication Lab. 2010-2011

7-  Start to transmit the data over optical fiber. Make sure the optical fiber

with no loops or bend.

8-  Plot the output signal on the graph paper

9-  By using bend board (25mm diameter part); bend the optical fiber

according to the figure of bending. Then plot the output signal on the

graph paper.

10-  Repeat step (9) with bending diameters (17.5mm, 15mm, 10mm, and

8mm).

Bending diameter

(mm)

Bending radius

(mm)

Optical power

(dBm)

Attenuation

(dB)

Results and Discussion

1-  Using the data from the table, carefully plot on a single graph the bending

loss in dB as a function of bend radius.

2-  Comment on the results.

3-  State the some application of the bending losses concept.