PHASE NOISE IN COHERENT ANALOG AM-WIRNA OPTICAL LINKS

Coherent analog amplitude modulated-wideband rectifier narrowband (AM- WIRNA) systems have been the focus of many recent studies because of t heir high performance and relative immunity to phase noise compared to angle modulated systems. Despite their natural advantages over angle modulated systems, AM-WIRNA receivers are still vulnerable to phase no ise because of distortion of their phase broadened signals in a finite bandwidth system. We present the first numerical analysis of the effe cts of this distortion on the performance of AM-WIRNA systems. The ana lysis accurately models the power spectral density of the phase-to-int ensity noise with a root-mean-square deviation from the averaged exper imental noise spectrum of 1.2 dB and a maximum deviation of 3.8 dB in the modulation range of <2 GHz. The accuracy of the analysis is limite d primarily by nonidealities in the AM-WIRNA receiver and the accuracy of the analytical intermediate frequency (IF) filter model. Optimal l ink designs are presented which minimize the impact of phase-to-distor tion noise in AM-WIRNA systems. We present experimental data from AM-W IRNA links which use both external cavity and distributed feedback las ers for the signal and local oscillator sources. The numerical analysi s predicts the link signal-to-noise ratio (SNR) for different signal l aser powers to within 1.4 dB of experiment. We find that systems requi ring high SNR such as phased array antennas and AM-CATV are significan tly affected by this noise.