Identifying the noise sources in an RF Photonic link allows us to determine the performance of the link and helps us to identify critical components to link and device design to develop a high performance link. Below is an intensity modulated optical link. Other modulation schemes in RF photonic links may be discussed at a later point.
Since the output of the RF photonic link is the photocurrent generated by the photodetector, the noise sources are a current noise power spectral density.
Noise sources from the laser:
Laser RIN (relative intensity noise) is the fluctuation of optical power. Relative intensity noise is the noise of the optical power divided by the average optical power in a laser. RIN noise originates from spontaneous radiative carrier recombination and photon generation.
Noise sources from the modulator:
Noise in a modulator is due to thermal noise of electrode termination and ohmic loss in the electrodes.
Noise sources from the photodetector:
Shot noise occurs as a result of the quantization of discrete charges or photons. Noise is also generated by the photodetector termination.
Total current noise power spectral density of the RF photonic link: