My schematic is as follows
The idea is that AC and DC signals can be split into two outputs separately. The photodiode is Hamamatsu's S3071 (Dark current less than 10nA). The laser light produces a DC signal of about 0.5 mA superimposed with a AC signal (500KHz) of ~1 uA. The DC Output is OK. But the AC output noise reachs more than 1V. This noise is still there even without light. And the noise between AD8015 pin 6,7 is about one-twentieth of the output signal noise, so the noise should have nothing to do with the second amplifier OPA847.
So my question is: Where does this noise come from and how can I lower it?
Thanks a lot.