PHOTON NOISE MUCH HIGHER THAN THERMAL NOISE AT OPTICAL WAVELENGTHS
Because of quantum noise effects, the noise associated with the statistical arrival of
optical photons is much higher than the normal thermal noise in electronic receivers. So
optical receivers are far noisier than radio-frequency receivers, and hence far less
sensitive.
Counter Argument
This is true. However, it can be shown that the effect of the much high Effective
Isotropic Radiated Powers (EIRPs) of optical uplinks is such to so increase the signal
strength at the targeted receiver, that it more than makes up for the increased receiver
noise. The bottom-line is that the link signal-to-noise ratio (SNR) is far superior.