How to obtain maximal voltage transfer?
Johnson noise density of a 50 ohm resistor is in the region of 0.5 nV/rtHz. So, given the photodetector voltage you're seeing, the bandwidth of interest, and the SNR you need (none of which you've told us) it's easy to check.

For example, if you are seeing 1mV rms signal, your bandwidth of interest is 1 MHz, and you need 40dB SNR ... 

Noise voltage is 0.5 * sqrt(1e6) nV or 500nV or 0.5 uV in 1 MHz bandwidth. That's 66dB below your 1mV signal, well below your 40db SNR requirement, so ... no problem.

But if you needed 60dB SNR, then the resistive noise contribution is significant and you'd have to consider the noise budget carefully.