The multilevel diffraction spectra of target image is obtained on the filtering plane because of the periodic structure of SLM in VLC

. Matched filters can be loaded at the position of different diffraction spectra on the filtering SLM to perform matched filtering of multilevel diffraction spectra. Theory analysis shows the correlation spots of different diffraction spectrums are at the same position of the output plane

and then the correlation peak value is enhanced by coherent superposition. It is verified by experiments that the output correlation peak of VLC can be effectively enhanced using this method.