This can be used as a low pass filter against shot noise, but so can be a purely electronic device, which will do it without an extra laser, and do it better.

This can be used as a low pass filter against shot noise, but so can be a purely electronic device, which will do it without an extra laser, and do it better. As for amplification role, 2 nanoseconds would too be too bad in comparison to existing optical amplifier, for which bandwidth is practically unlimited (many terrahertz.) As for its utility as a more compact alternative to optical amplifiers for use cases where you don't need much bandwidth, you still have that second laser input, instead of which you could've put a still much smaller electronic amplifier, which would still be needed for the final optical->electrical conversion.