Question

The optic power, after propagating through a fibre that is 500 m long is reduced to 25% of its original value.Calculate the fibre loss in dB/km.

Answer 1

Answer on Question #69841, Physics / Optics

The optic power, after propagating through a fibre that is 500 m long is reduced to 25% of its original value. Calculate the fibre loss in dB/km.

Solution:

The loss of the power in a fibre (in dB/km) is given by

$$\frac {10 \lg \frac {\text{output power}}{\text{input power}}}{\text{distance}}$$

So, in our case the fibre loss

$$\frac {10 \lg \frac {1/4 P _ {0}}{P _ {0}}}{0.5} = 20 \lg \frac {1}{4} = - 12 \frac {\mathrm{dB}}{\mathrm{km}}.$$

Answer: $-12\frac{\mathrm{dB}}{\mathrm{km}}$

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