Phase imaging is widely used in biomedical imaging, sensing, and material characterization, among other fields. However, direct imaging of phase objects with subwavelength resolution remains a challenge. Here, we demonstrate subwavelength imaging of phase and amplitude objects based on all-optical diffractive encoding and decoding. To resolve subwavelength features of an object, the diffractive imager uses a thin, high-index solid-immersion layer to transmit high-frequency information of the object to a spatially-optimized diffractive encoder, which converts/encodes high-frequency information of the input into low-frequency spatial modes for transmission through air. The subsequent diffractive decoder layers (in air) are jointly designed with the encoder using deep-learning-based optimization, and communicate with the encoder layer to create magnified images of input objects at its output, revealing subwavelength features that would otherwise be washed away due to diffraction limit. We demonstrate that this all-optical collaboration between a diffractive solid-immersion encoder and the following decoder layers in air can resolve subwavelength phase and amplitude features of input objects in a highly compact design. To experimentally demonstrate its proof-of-concept, we used terahertz radiation and developed a fabrication method for creating monolithic multi-layer diffractive processors. Through these monolithically fabricated diffractive encoder-decoder pairs, we demonstrated phase-to-intensity transformations and all-optically reconstructed subwavelength phase features of input objects by directly transforming them into magnified intensity features at the output. This solid-immersion-based diffractive imager, with its compact and cost-effective design, can find wide-ranging applications in bioimaging, endoscopy, sensing and materials characterization.

翻译：相位成像广泛应用于生物医学成像、传感及材料表征等领域，然而对具有亚波长分辨率的相位物体直接成像仍具挑战性。本文基于全光衍射编码与解码技术，实现了相位与振幅物体的亚波长成像。为解析物体亚波长特征，该衍射成像器采用薄层高折射率固体浸没介质，将物体高频信息传输至空间优化的衍射编码器，该编码器将输入高频信息转换为低频空间模式以通过空气传输。后续空气介质中的衍射解码层与编码器通过基于深度学习的优化联合设计，与编码层协同作用，在其输出端生成输入物体的放大图像，揭示原本因衍射极限而湮灭的亚波长特征。我们证明，这种衍射固体浸没编码器与后续空气解码层之间的全光协作，能以高度紧凑的设计解析输入物体的亚波长相位与振幅特征。为实验验证概念可行性，采用太赫兹辐射并开发了单片多层衍射处理器的制备方法。通过单片集成的衍射编码-解码对，展示了相位-强度变换，并实现了输入物体亚波长相位特征的全光重建——直接将其转化为输出端放大的强度特征。这种基于固体浸没的衍射成像器凭借紧凑低成本的特性，在生物成像、内窥镜、传感及材料表征领域具有广阔应用前景。