###### Abstract  
All-optical matching systems that detect and localize designated target sequences in input all-optical data sequences have attracted significant attention in all-optical processing. They have various applications, including all-optical intrusion detection, optical frame alignment, and optical package identification. In real-world applications, noise is inevitable and can lead to incorrect matching results. In particular, noise accumulates in serial all-optical matching systems, rendering the systems useless after several cycles. In this study, we developed a scheme for suppressing noise in quadrature phase-shift-keying (QPSK)-oriented all-optical matching systems. First, we evaluated the impact of input and amplifier noise on a QPSK-oriented all-optical matching system at a transmission rate of 100 Gbaud. We then developed a second-order noise-suppression structure using a highly nonlinear fiber (HNLF). With an input optical signal-to-noise ratio (OSNR) of 6 dB and an amplifier noise figure (NF) of 4 dB, the QPSK-oriented all-optical matching system without the noise-suppression structure output incorrect results. However, when the system was optimized using the proposed noise-suppression structure, correct matching results were obtained. Furthermore, when the NF of the amplifiers was fixed at 4 dB, the optimized system could reduce the minimum input OSNR to 0 dB. With an input OSNR of 0 dB, the logarithm of the bit error rate (BER) of the output matching results of the optimized system tended to negative infinity. The extinction ratio (ER), contrast ratio (CR), and quality (Q) factor of the output of the optimized system were 154.9532, 166.94289, and 161.12 dB, respectively, indicating high noise resistance. These results demonstrate that the system optimized using the proposed noise-suppression scheme exhibits high stability and reliability in noisy environments. all-optical matching system; noise suppression; highly nonlinear fiber; signal quality +
Footnote †: journal: _photonics_  
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and intrusion detection at the optical layer can be used as a high-speed and low-energy network security tool. Wirespeed Security Domains using Optical Monitoring (WISDOM), a European Union project, was the first photonic firewall developed [7]. The all-optical matching system is a core part of the photonic firewall. It comprises all-optical logic gates, such as the AND, NOT, and XOR gates, which can be obtained using dielectric waveguides [8; 9], semiconductor optical amplifiers (SOAs) [10; 11; 12], highly nonlinear fiber (HNLF) [13], etc. Several structures of all-optical matching systems have been developed. In [13], the authors proposed an all-optical matching system for on-off keying (OOK)-modulated optical signals based on the effects of cross-phase modulation (XPM) and four-wave mixing (FWM) in HNLF. In this system, the data rate of the optical signal can reach 160 Gbps. [PERSON] et al. proposed an all-optical matching system for optical signals modulated by quadrature phase-shift keying (QPSK) [14]. This system simultaneously identifies the in-phase (I) and orthogonal (Q) branches, and recognition of the entire target pattern depends on whether the highest level is in the same symbol in the electrical domain and requires complicated synchronization technology. [PERSON] et al. also proposed an all-optical matching system based on interference effects [15]. The system is suitable for any amplitude- and phase-modulation format. In the simulations, optical signals with a symbol rate of 100 GBaud and modulation formats of binary phase-shift keying (BPSK), QPSK, 8-phase-shift keying (8 PSK), and 16-quadrature amplitude modulation (16 QAM) were verified. [PERSON] et al. proposed a reconfigurable all-optical pattern-matching system based on phase-sensitive amplification (PSA) using HNLF [16].