Bit error rate calculations for a photodiode receiver driven from a laser
The one thing that jumps out as odd, is that photo sensitivity in V/mw which tells me that you can't just use P=V^2/R to get from noise power to noise voltage. 

Since it also talks about "noise equivalent power" that tells me that they are referring the output noise voltage back to an equivalent optical power (presumably to cater for different load impedances or something) or maybe that's just the most convenient form of specification for comparing different optical sensors. However, that suggests you should apply the "photo sensitivity" to the noise power to generate your noise voltage.

Which makes the rms noise 1.5*310e-6 or more like 465uv.

Does the BER make more sense if you do that?