Here’s a brief on how Spectral Amplitude Coding (SAC) was done using Walsh Code :
We have 4 wavelength values –
lamda 1 = 1550 nm
lamda 2 = 1550.8 nm
lamda 3 = 1551.6 nm
lamda 4 = 1552.4 nm
Walsh code for Encoding :
User 1 (1010) : 2 FBGs at encoder coded with lamba 1 and lamda 3 (lamda 2,4 are cut off)
User 2 (1100) : 2 FBGs at encoder coded with lamba 1 and lamda 2
User 3 (1001) : 2 FBGs at encoder coded with lamba 1 and lamda 4
Walsh code for decoding using complementary/balanced detection :
User 1 (1010) : 2 top FBGs at decoder coded with lamba 1 and lamda 3, 2 bottom FBGs at decoder coded with lamba 2 and lamda 4
User 2 (1100) : 2 top FBGs at decoder coded with lamba 1 and lamda 2, 2 bottom FBGs at decoder coded with lamba 3 and lamda 4
User 3 (1001) : 2 top FBGs at decoder coded with lamba 1 and lamda 4, 2 bottom FBGs at decoder coded with lamba 2 and lamda 3