To improve the physical-layer data confidentiality in short-reach optical networks, we have proposed an
M-ary blockciphered system using an optical code multiplexing approach. In a previous system, each optical code (OC), that corresponds to a frequency subcarrier, was mapped onto one of the log
2M bits, and the computational security is related to the correspondence between the bit-block and the OC, and the number of possible combinations equates
M!. However, this system presents two critical issues (1)
Computational Security: the number
M of OCs that can be generated by an optical arrayed waveguide grating (AWG) is limited, due to the port number and the subcarrier crosstalk. (2)
Physical security: a careful differential analysis of the corresponding time waveform, optical power, and/or optical spectrum can be used to identify the symbol pattern.
To mitigate the effects of interchannel interference, we propose a new differential phase-shift keying (DPSK)-based multi-dimensional
M-ary block ciphering system, that assigns binary phase difference patterns to adjacent symbols and demonstrate a 16-dimensional 2
16-ary ciphered system. In addition, to increase the
M-ary number, without increasing the number of OCs, we consider also a differential quadrature phase-shift keying (DQPSK)-based multi-dimensional
M-ary block ciphered system and demonstrate a 16-dimensional 2
32-ary ciphered system.