Question

A Si pin photodiode has a quoted noise equivalent power (NEP) of 1.3 x 10-3 w ㎐12 What is the optical signal power it needs for a signal to noise ratio (SNR) of 1 if the bandwidth of operation is 2GHz? (Q.38-3 marks)

Answer 1

Noise equivalent power of si pin photo diode (N E P) = 1.3 times 10^- 13 w/squareroot H g bandwidth of operation (B W) = 2 G Hz we know that noise power = N E P times squareroot B W = 1.3 times 10^- 13 w squareroot 2 times 10^9 squareroot Hz = 1.3 times 10^- 13 w squareroot 20 times 10^4 = 1.3 times 10^9 times 2 times squareroot 5 w = 2.6 times squareroot 5 times 10^- 9 w = 5.8136 times 10^- 9 w = 5.8136 n W given S N R (signal to noise ratio) = 1 therefore S N R = input signal power/noise power therefore noise power = input signal power (S N R = 1) therefore optical signal power = 5.8136 nw