Unidirectional imagers form images of input objects only in one direction, e.g., from field-of-view (FOV) A to FOV B, while blocking the image formation in the reverse direction, from FOV B to FOV A. Here, we report unidirectional imaging under spatially partially coherent light and demonstrate high-quality imaging only in the forward direction (A → B) with high power efficiency while distorting the image formation in the backward direction (B → A) along with low power efficiency. Our reciprocal design features a set of spatially engineered linear diffractive layers that are statistically optimized for partially coherent illumination with a given phase correlation length. Our analyses reveal that when illuminated by a partially coherent beam with a correlation length of ≥∼1.5λ, where λ is the wavelength of light, diffractive unidirectional imagers achieve robust performance, exhibiting asymmetric imaging performance between the forward and backward directions—as desired. A partially coherent unidirectional imager designed with a smaller correlation length of <1.5λ still supports unidirectional image transmission but with a reduced figure of merit. These partially coherent diffractive unidirectional imagers are compact (axially spanning <75λ), polarization-independent, and compatible with various types of illumination sources, making them well-suited for applications in asymmetric visual information processing and communication.
We introduce an information hiding-decoding system, which employs a passive diffractive processor as the front-end and an electronic decoder as the back-end, offering a fast, energy-efficient, and scalable solution for protecting visual information. This diffractive processor all-optically transforms arbitrary input messages into deceptive output patterns, decipherable only through a jointly-trained electronic decoder neural network. This method can successfully hide infinitely many input messages into ordinary-looking patterns at its output field-of-view, which can be subsequently decoded by an electronic network. We experimentally validated the feasibility of our information-hiding camera by 3D-printing a physical diffractive system and testing it under terahertz illumination.
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