Complex-valued universal linear transformations and image encryption using spatially incoherent diffractive networks

TL;DR

This paper demonstrates that spatially incoherent diffractive neural networks can perform complex-valued linear transformations and be used for all-optical image encryption, expanding their capabilities under natural lighting conditions.

Contribution

The study introduces the use of incoherent light in diffractive neural networks for complex-valued processing and image encryption, a novel extension of prior coherent-light-based methods.

Findings

Spatially incoherent D2NNs can approximate any complex linear transformation.

Performance improves as the number of diffractive features increases beyond a threshold.

The approach enables all-optical image encryption with incoherent illumination.

Abstract

As an optical processor, a Diffractive Deep Neural Network (D2NN) utilizes engineered diffractive surfaces designed through machine learning to perform all-optical information processing, completing its tasks at the speed of light propagation through thin optical layers. With sufficient degrees-of-freedom, D2NNs can perform arbitrary complex-valued linear transformations using spatially coherent light. Similarly, D2NNs can also perform arbitrary linear intensity transformations with spatially incoherent illumination; however, under spatially incoherent light, these transformations are non-negative, acting on diffraction-limited optical intensity patterns at the input field-of-view (FOV). Here, we expand the use of spatially incoherent D2NNs to complex-valued information processing for executing arbitrary complex-valued linear transformations using spatially incoherent light. Through simulations, we show that as the number of optimized diffractive features increases beyond a threshold dictated by the multiplication of the input and output space-bandwidth products, a spatially incoherent diffractive visual processor can approximate any complex-valued linear transformation and be used for all-optical image encryption using incoherent illumination. The findings are important for the all-optical processing of information under natural light using various forms of diffractive surface-based optical processors.