Additive phase noise suppression of direct modulation analog optical links

The relativity between the additive phase noise of a direct modulation analog optical link and the RF power level as well as the relativity between the additive phase noise of this link and the average optical power at the photodetector's (PD) input are experimentally investigated. The results show the phase noise far from the carrier can be suppressed by setting the RF power level to the maximum achievable while keeping the PD operate under the proper saturation status. Through link optimization, the difference of phase noise at the frequency offset ≥100 kHz between signal generated from frequency source and the one after link transmission has been reduced to ≤5dB. Furthermore, the phase noise at the near frequency offset is proved to be mainly caused by up-converted low frequency intensity noise and can be suppressed when reducing the laser RIN.