Subwavelength Imaging using a Solid-Immersion Diffractive Optical
  Processor
Jingtian Hu Kun Liao Niyazi Ulas Dinc Carlo Gigli Bijie Bai Tianyi Gan Xurong Li Hanlong Chen Xilin Yang Yuhang Li Cagatay Isil Md Sadman Sakib Rahman Jingxi Li Xiaoyong Hu Mona Jarrahi Demetri Psaltis Aydogan Ozcan
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.