Different types of OTDR measurement.

Only simply descriptions of the different types of measurement that can be carried out with an OTDR are given in the following. For more detailed information refer to the instrument meanufacturer’s manual.

1** Distance measurement.

Using an OTDR, the length of an optical fiber can be determined with a high degree of accuracy.

L=              vt/2=ct/2n

V =            velocity of light in the optical fiber

T =             propagation time (s)

L =             length of the optical fiber (m)

E =            velocity of light in a vacuum (m)

N =            refractive index of the core

2**Optical power loss (attenuation

Because power is shown on the vertical axis, the power less can be osciculated by subtracting one power level from another.

A(a)=p₁-p₂/2

Optical power loss per unit of length (Lu)

A(a) = p_1-p₂/2L

OTDR Curve and its use in attenuation measurement

3**Splice loss measurement.

When an OTDR is used for measurement, the graph obtained shows the attenuation in a cable section. If the section contains splices (either mechanical or fusion splices) these are normally shown as knees on the graph. The loss in each splice can be determined by measuring in these points – either according to the two point method or the five point method.