Unidirectional imaging with partially coherent light

TL;DR

This paper introduces a novel unidirectional imaging device using spatially engineered diffractive layers optimized for partially coherent light, enabling high-quality forward imaging with low backward efficiency, suitable for compact and versatile applications.

Contribution

The work presents the first design of unidirectional imagers that operate effectively under partially coherent illumination, with statistical optimization for different phase correlation lengths.

Findings

Achieves robust unidirectional imaging with correlation length ≥ 1.5w

Supports unidirectional image transmission with smaller correlation lengths

Device is compact, polarization-independent, and compatible with various light sources

Abstract

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 ~1.5 w or larger, where w 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 less than 1.5 w still supports unidirectional image transmission, but with a reduced figure of merit. These partially coherent diffractive unidirectional imagers are compact (axially spanning less than 75 w), polarization-independent, and compatible with various types of illumination sources, making them well-suited for applications in asymmetric visual information processing and communication.