Demonstration of optical pattern matching between two QPSK data channels using nonlinear wave mixing

Optical signal processing can provide high-speed operation on optical data and avoidance of optical-to-electrical-to-optical conversion. In many networking scenarios, the optical data may be encoded as quadrature-phase-shift-keying (QPSK) for spectral efficiency and noise tolerance. One signal processing function is pattern matching between two data streams, which directly compares their data patterns and can be useful for network security and improving data transmission. In this work, we experimentally demonstrate optical pattern matching between two independent QPSK data inputs using nonlinear wave mixing. The QPSK channels and their delayed copies are combined at the input of a highly nonlinear fiber (HNLF) along with a continuous wave pump. The data channels and pump undergo four-wave mixing in the HNLF to generate a 9-ary quadrature amplitude modulation (9-QAM) output. The output symbols correspond to the matched, partially matched, and mismatched 2-symbol patterns between the two QPSK inputs. The 9-QAM output constellation has an error-vector-magnitude of 8.4% and 8.9% at 3-Gbaud and 5-Gbaud rates, respectively, resulting in error-free optical pattern matching between the two QPSK inputs over 1536 symbols.