Abstract
Based on the proposed self-coherent detection, several comparisons among coherent detection, direct detection and self-coherent detection is being made in this work. The system performance of self-coherent detection which adopts balanced receiver has a 3-dB penalty to the system performance of coherent detection. The difference comes from the existence of carrier in transmitted signal in self-coherent detection when the carrier to signal power ratio is set to one. The effects of different filter bandwidths will be discussed, especially for coherent detection and self-coherent detection. Some theoretical analysis will be made to explain the resemblance between them. After then, the spectrally matched optical filters are used to refine the system performance and approach coherent detection as possible. The limitation of laser linewidth is taken into consideration here. To optimize the system performance, optical carrier filters of different bandwidths and different order will be uesd. We find that higher order filters may cause serious phase distortion when the optical filter bandwidth is too small, while lower order optical filters cannot stop the ASE noise from passing through with the OFDM signal. When the laser linewidth equals 1MHz, to get the optimized system performance, 50MHz 1st order Gaussian filter is used as the carrier filter. Then, the issue of spectral efficiency is being discussed. At the beginning, the noise mechanism of self-coherent detection which adopts either single-end receiver or the balanced receiver is studied. Besides, some numerical simulations are made. The result derived from the simulations is consistent with the theoretical result. The system performance of self-coherent detection is invariant when balanced receiver is adopted while it changes significantly when single-end receiver is adopted.