You have named three wavelengths for a code of length 8 and with four ‘1’s, while four FBGs with four different wavelengths should have been used. Are you sure about the wavelengths used in the paper?
I suggest that you design the system with central wavelength of 1550.5 with steps of 0.5nm and bandwidth of 0.3nm and choose the receiver FBG wavelengths as you earlier mentioned (by using complements). If you did not get the answer, please attach the file here.