Constellation manipulation-enabled multi-symbol optical pattern recognition in photonic firewalls

This paper proposes a direct recognition system for optical patterns in photonic firewalls that is essential for enhancing the security of optical transmission networks. High-order modulation multi-symbol pattern direct recognition is achieved with the proposed low-complexity, feedback-free system, which is enabled by multi-dimensional constellation manipulations. Incoming binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) symbol patterns are firstly mapped onto quadrature amplitude modulation (QAM) constellations via optical time-delay and phase-rotating stages. A nondegenerate phase-sensitive amplifier then performs optical vector-moving, thereby converting the combined QAM constellations into pulse amplitude modulation formats suitable for direct amplitude detection. The detailed theoretical derivations are provided for the processes of optical time delay, phase rotation, and vector moving. The eye diagrams, constellations, and received power distributions of the input and recognized patterns are measured and depicted. False detection ratio (FDR) is defined and used as a quantitative measure of system performance under different signal qualities. At the FDR of 10^-3, with the input optical signal-to-noise ratio (OSNR) of 20 dB, the BPSK eight-symbol patterns show the receiver OSNRs around 16.6 dB, and the QPSK eight-symbol patterns show the receiver OSNRs around 21.7 dB. The proposed constellation manipulation-enabled direct recognition system offers an efficient and compatible solution for recognizing high-order modulation patterns, establishing a viable path toward robust, all-optical security modules in future optical networks.