Question

A fiber optic receiver has a sensitivity of -38 dBm. This is the optical power required to operate with the desired mesage quality. The transmitter produces a power level of 4 dBm. What are the allowed system losses in dB? These losses are caused by inefficient coupling from the transmitter into the fiber, by connector and splice losses, and by losses in the fiber itself.

Answer 1

Clearly in the question, allowed system losses in dB is asked.

Optical fiber receiver sensitivity = - 38 dBm.

Optical fiber transmitter sensitivity = 4 dBm.

Thus Power at output = Receiver sensitivity = Po = -38 dBm.

Power at input = Transmitter sensitivity = P _in = 4 dbm

Allowed loss = P _in - P _o = 4dBm - (-38 dBm) = 42 dB.

To be taken care of is whenever power in dBm is subtracted then the answer will be in dB as dBm represents the quantity in log and when they are subtracted it becomes division inside logarithmic arguement, thus canceling the mili or 10^-3 term and giving only the term in dB.

Thus allowed loss = 42dB.

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