Wavelength by design: A comprehensive review of spectral diffractive optical elements

Spectral diffractive optical elements (DOEs) have emerged as powerful tools for wavelength-selective manipulation of light in compact, planar formats. This review provides a comprehensive overview of the principles, design methodologies, fabrication techniques, and application landscapes of spectral DOEs. Emphasizing their spectral sensitivity and phase-engineering capabilities, we examine how DOEs enable functionalities such as dispersion control, wavelength multiplexing, chromatic aberration correction, and hyperspectral imaging. Key design strategies including analytical models, iterative optimization, and inverse design methods are discussed alongside advancements in fabrication approaches such as grayscale lithography, nanoimprint lithography, and two-photon polymerization. Material platforms from fused silica and silicon to polymers are evaluated for their spectral, mechanical, and environmental performance. Application domains span imaging systems, optical communications, spectroscopy, AR/VR displays, and solar energy harvesting. We also explore emerging directions such as multilayer and 3D diffractive structures, tunable DOEs, metasurface-enhanced hybrids, and AI-driven design automation. While spectral DOEs offer significant advantages in scalability, functionality, and integration, challenges remain in broadband efficiency, fabrication precision, and polarization control. This review highlights current limitations and identifies promising pathways for overcoming them, positioning spectral DOEs as critical components in next-generation photonic systems.