4<i>f</i>‐Less Terahertz Optical Pattern Recognition Enabled by Complex Amplitude Modulating Metasurface Through Laser Direct Writing

Optical pattern recognition (OPR) has the advantage of single intensity detection ability for low-cost terahertz (THz) systems imaging or security checks. However, conventional 4f-system-based OPR is limited by paraxial approximation and bulky device volumes THz applications. Here, a full-diffraction-based 4f-less method proposed using complex-amplitude-modulating metasurface, which valid with large Fresnel numbers. Moreover, laser-induced graphene technique applied processing device. A 15 mm × metasurface can be fabricated one-step laser writing in 34 s, indicating potential developing miniaturization, fast fabrication, low-cost.