The influence of light source linewidth on power spectrum of four light coherent mixing signal

The four-optical coherent mixing detection technology can improve the dynamic range of moving target detection. This method has the difficulty of distinguishing the type of mixing output signal. We propose a method to distinguish the signal type by using the different peaks of the mixed signal spectrum. Based on the statistical theory, the power spectrum function of the mixed signal is obtained, and the numerical analysis of the influence of the light source line width and the light source frequency difference on the signal power spectrum is carried out. Through numerical calculation and analysis, the results show that the increase of the light source linewidth will lead to the broadening of the signal power spectrum. When the Doppler frequency difference is greater than 1/5 times the linewidth of the light source, the power spectrum of the two homodyne coherent signals in the four-light coherent mixing can be distinguished; when the Doppler frequency difference is less than 1/5 times the light source linewidth, The power spectrum of the two homodyne coherent signals in four-optical coherent mixing can not be distinguished.