A silicon pin photodiode has a quantum efficiency of 65 at a

A silicon p-i-n photodiode has a quantum efficiency of 65% at a wavelength of 0.8 mu m. Determine: the mean photocurrent when the detector is illuminated at a wavelength of 0.8 mu m with 5 mu W of optical power; the rms quantum noise current in a post-detection bandwidth of 20 MHz; the SNR in dB, when the mean photocurrent is the signal.

Solution

a). = (I_ph/e)/(Po/h_v)

P_oe/h_v=I_ph

I_{ph= mean photo current}

= Quantum efficiency

P_o= Optical power

so calculating the following Iph= 2.01 microAmps

b.) Rms value of the fluctuations = Shot noise current

I_n = [2eI_dB]^1/2

calculating the value we get= 3.59 nanoAmps

c.) SNR= Iph ²/I_n²

calculating the value we get 55dB