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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.

We demonstrated an efficient scheme of measuring the angular velocity of a rotating object with the detection light working at the infrared regime. Our method benefits from the combination of second-harmonic generation (SHG) and rotational Doppler effect, i.e., frequency upconversion detection of rotational Doppler effect. In our experiment, we use one infrared light as the fundamental wave (FW) to probe the rotating objects while preparing the other FW to carry the desired superpositions of orbital angular momentum. Then these two FWs are mixed collinearly in a potassium titanyl phosphate crystal via type II phase matching, which produces the visible second-harmonic light wave. The experimental results show that both the angular velocity and geometric symmetry of rotating objects can be identified from the detected frequency-shift signals at the photon-count level. Our scheme will find potential applications in infrared monitoring.

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