Evaluation of the un-eliminated laser phase noise induced by interferometer imbalance in self-homodyne coherent optical RF receivers

Coherent optical RF receivers constructed in self-homodyne configurations have gained considerable attention due to its simplicity and cost-efficiency. Rigorous symmetry is required in such system to suppress the laser phase noise. A method for evaluation of the un-eliminated laser phase noise in self-homodyne coherent optical RF receivers has been presented in this paper. In our proposed scheme, the un-eliminated laser phase noise is acquired by simply inserting an FBG in the in-phase arm and is found to be dependent on the interferometer asymmetry, i.e., the path imbalance of the interferometer arms. With series of simulations, the variance of the un-eliminated laser phase noise obtained by our method becomes larger when the path imbalance is increasing. The simulation results show that, variance increases with the asymmetrical time delays of two interferometer arms. Therefore, this method is very helpful in obtaining further insight into the system symmetry and is also a good guidance for the adjustment of the interferometer architecture to achieve the optimized path equality.