A transmitter has an output power of 0.1 mW. It is used with a fiber having NA= 0.25, attenuation of 6 dB/km, and length of 0.5 km. The link contains two connectors with a 2 dB average loss. The receiver has a minimum acceptable power (sensitivity) of – 35 dBm. The designer has allowed a 4 dB margin. Calculate the link power budget.

Solution:

Source power Ps

$=0.1 \mathrm{~mW}$

$P_s=-10 \mathrm{dBm}\\ $

Since $\quad N A=0.25$

Coupling loss

$=-10 \log \left(N A^2\right)$

$=-10 \log \left(0.25^2\right)\\ $

$=12 \mathrm{~dB}\\ $

Fiber loss $=\alpha_f \times L$

$I_f=(6 \mathrm{~dB} / \mathrm{km})(0.5 \mathrm{~km}) \mathrm{I}_{\mathrm{f}}=3 \mathrm{~dB}\\ $

Connector loss $=2(2 \mathrm{~dB})$

$ I_c=4 \mathrm{~dB} …