What bandwidth is needed for an arbitrary digital signal?
At full data rate, you have a square wave that is 25 MHz and if you have a 3dB bandwidth of 75 MHz you'll pass the 3rd harmonic through without too much loss of shape. It won't look perfect but the eye pattern will be good enough. Below shows how the square wave is "built" from its harmonics. The picture after the sinewave at the fundamental is the "square wave that only contains the 3rd harmonic and, hopefull you can see that it is still fairly reasonable in shape: -



Eye patterns for data that has been restricted in bandwidth are also a useful source of information. For instance the one below pretty much looks like data that contains very few harmonics: -



The above informs anyone who knows about data transmission systems that the eye pattern shape is pretty good and easily converted back to proper logic levels - it's the amount of white space (surronded by the red traces) that gives confidence here. Maybe you should study eye diagrams.

You can also use tools like LTSpice for simulating data that has been bandlimited in order to figure out detection regimes that will work. You have to contend with noise, poor rise (and fall) times, small amplitudes and inter-symbol distortion. It's do-able.

You can buy off the shelf solutions that are good for at least 4 times your data rate and don't cost the earth. I have built links that are good for 700 Mbps that use 1 GHz bandwidth optics so that should set some form of benchmark for you.