Question

An edge-emitting LED operating at a wavelength of 1.3 μm launches −22 dBm of optical 

power into a single-mode fiber pigtail. The pigtail is connected to a singlemode fiber link 

which exhibits an attenuation of 0.4 dB km−1

at this wavelength. In addition, the splice losses 

on the link provide an average loss of 0.05 dB km−1. The transmission rate of the system is 

280 Mbit s−1

so that the sensitivity of the p–i–n photodiode receiver is −35 dBm. Penalties on 

the link require an allowance of 1.5 dB and a safety margin of 6 dB is also specified. If the 

connector losses at the LED transmitter and p–i–n photodiode receiver are each 1 dB, 

calculate the un-repeatered distance over which the link will operate.​

Answer 1

Answer:

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Answer 2

Given:

An edge-emitting LED

wavelength λ$=1.3$ μm

Power at the transmitter $P_{i}=-22\ dBm$

cabled fiber loss $\alpha _{fc}=0.4$

Splice loss $\alpha _{j}$$=0.05\ dBkm^{-1}$

Sensitivity $P_{o}=-35\ dBm$

allowance, $D_{L}=1.5\ dB$

Required safety margin, $M_{a}=6\ dB$

The system operated at $280\ mbit\ s^{-1}$

To Find:  

The un-repeated distance over which the link will operate

Solution:

Use optical power budget equation

$P_{i}-P_{o}=(\alpha _{fc}+\alpha _{j})L+\alpha _{cr}+D_{L}+M_{a}\\-22-(-35)=(0.4+0.05)L+2+1.5+6\\13=0.45L+9.5\\3.5=0.45L\\L=\dfrac{3.5}{0.45}\\L=7.8\ km$

The un-repeated distance above the link will operate is 7.8 km.