How to calculate noise power (dBm) of a photodiode?
The noise power quoted in most photodiode data sheets is actually noise equivalent power and the "equivalence" is related to the incident light power on the device. Incident power gets converted to photodiode current so you have to have your PD in situ in a circuit to make sense. If you are using a TIA then that current becomes a voltage and then you can more readily measure it on an oscilloscope.