# Place of matched filter in fiber optic communication

1. In short-haul communication via optical fibers, we use photodiodes (PD) to detect the light. So if we want to use a matched filter, should we use it before the PD (optical domain) or after the PD (electrical domain)?
2. If we use it after the PD, should its impulse response be $$h(t)=s(T-t)^2$$ due to the square law property of PD?
• What function does the filter perform i.e. what is it there to do? – Andy aka Jul 13 '17 at 8:57
• @Andyaka matched filter is used to maximize the SNR in systems which the noise is AWGN – CLAUDE Jul 13 '17 at 16:01
• AWGN what does that mean? Also how much light noise entering the photodiode optically do you expect compared to what the photodiode self generates? How does this filter maximise the SNR? – Andy aka Jul 13 '17 at 16:28
• @Andyaka I can show mathematically how it maximizes the SNR, but what does it do in reality? I don't know. I have no sense of the amount of noise entering the photodiode and the noise generated in it. – CLAUDE Jul 13 '17 at 17:14
• Maybe you can provide a link to what this filter is and how it does it? – Andy aka Jul 13 '17 at 18:37