Optimizing Structured Surfaces for Diffractive Waveguides

TL;DR

This paper presents a universal, deep learning-optimized diffractive waveguide platform capable of versatile functionalities, low-loss guiding, and spectral scalability, validated in the terahertz spectrum with potential for broad optical applications.

Contribution

Introduces a novel diffractive waveguide design framework that is highly versatile, scalable across wavelengths, and capable of complex functionalities without traditional dispersion engineering.

Findings

Achieved low-loss, high mode purity guidance in THz spectrum

Demonstrated waveguide components like bends, filters, and splitters

Validated designs through experimental 3D-printed prototypes

Abstract

Waveguide design is crucial in developing efficient light delivery systems, requiring meticulous material selection, precise manufacturing, and rigorous performance optimization, including dispersion engineering. Here, we introduce universal diffractive waveguide designs that can match the performance of any conventional dielectric waveguide and achieve various functionalities. Optimized using deep learning, our diffractive waveguide designs can be cascaded to each other to form any desired length and are comprised of transmissive diffractive surfaces that permit the propagation of desired guided modes with low loss and high mode purity. In addition to guiding the targeted modes along the propagation direction through cascaded diffractive units, we also developed various waveguide components and introduced bent diffractive waveguides, rotating the direction of mode propagation, as well as spatial and spectral mode filtering and mode splitting diffractive waveguide designs, and mode-specific polarization-maintaining diffractive waveguides, showcasing the versatility of this platform. This diffractive waveguide framework was experimentally validated in the terahertz (THz) spectrum using 3D-printed diffractive layers to selectively pass certain spatial modes while rejecting others. Diffractive waveguides can be scaled to operate at different wavelengths, including visible and infrared parts of the spectrum, without the need for material dispersion engineering, providing an alternative to traditional waveguide components. This advancement will have potential applications in telecommunications, imaging, sensing and spectroscopy, among others.