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In this thesis, we analyze and simulate the performance of the optical coherent heterodyne analog AM and FM communication systems. The FM receiver uses a discriminator and the AM receiver utilizes envelope detection. The theoretical analyses are presented and verified by simulation. The results show that the SNR floor exists in both cases. The coherent analog systems are seriously impacted by the lasers phase noise. Hence, the requirement of the laser linewidth is very stringent. We also find that the IF filter bandwidth has great influence on the performance of the AM system.
In addition, a dual-frequency-type phase-noise-cancelling scheme is applied to improve the performance of the FM system. The analytic result is obtained and compared with that of the FM system without phase-noise cancelling. We can significantly reduce the SNR floor when the difference between the two path is small. This makes the coherent FM system more applicable.
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