While APDs do have internal gain and consequently a greater power output, they need a higher voltage supplied to them. Unfortunately, this supply voltage increases the Dark Noise in the system and the gain increases noise in general. PIN Photodiodes, on the other hand, do not have internal gain and subsequently lower noise.
=> PIN Photodiodes are preferable.
Detector Characteristics:
- Low rise time,
- Low dark noise,
- Low NEP,
- Low Cost,
- High Frequency.
- High S/N Ratio
MenloSystems' FPD510 fits these requirements quite well, having a Dark noise level of -120dBm, NEP of 3pw/(Hz^1/2) and a maximum frequency of 250MHz. The rise time is 2ns and, while this is higher than the rise time of the FPD310, the FPD310 has a Dark noise level of -90dBm and NEP of 15.7pw/(Hz^1/2).
Although this detector fits most criteria, we're still on the lookout incase another, better detector is out there.
