Second harmonic generation based joint transform correlator for human face and QR code recognitions

We propose a nonlinear joint transform correlator (JTC) based on a joint power spectrum via second-harmonic generation (SHG) in the Fourier domain. The fundamental waves of 1064 nm infrared light illuminate the images displayed by a single spatial light modulator. After SHG in a type-II potassium titanyl phosphate crystal in the Fourier domain, the second-harmonic wave of 532 nm visible light yields the correlation signal. We demonstrate the performance of our SHG-based JTC for human face recognition and quick response code recognition. Our work has the potential in various optical information processing applications such as infrared pattern recognition and remote sensing, security verification, target tracking, and optical computing.