Employing two-dimensional CT codes with two-code keying in optical CDMA systems

We propose a novel code family—two-dimensional (2-D) cotw (CT) codes with two code keying (TCK)—designed for polarization, spectral code sequences, and spatial code sequences of the optical code multiple access (OCDMA). Polarization requires two mutually orthogonal states of polarization (SOPs). The proposed system incorporates innovative two mutually orthogonal SOPs within the optical line terminal (OLT), offering advantages for encoding transmitter code sequences. This transmitter design using the advanced encoder can efficiently support total simultaneous users. At the receiver, optical network units (ONUs) utilize the 2-D CT codes with TCK, which effectively eliminates multi-user interference (MUI) and suppresses phase-induced intensity noise (PIIN). The 2-D CT codes evolve from one-code keying (OCK) to TCK. Numerical results demonstrate that the proposed 2-D CT codes with TCK attain a bit error rate (BER) of 10⁻⁹ with total simultaneous users, a received source power of −15.10 dBm, and a data transmission rate of 7.22 Gbps.