A New Frontier in Unidirectional Light Control with Diffractive Optics
The Californer/10308513

LOS ANGELES - Californer -- Controlling asymmetric light propagation—where light preferentially travels in one direction while being blocked or scattered in the opposite direction—has been a longstanding need in optical systems. Traditional solutions often rely on specialized material properties or nonlinear materials, which require relatively complex and costly fabrication methods, bulky hardware, and high-power laser sources. Other approaches, including asymmetric gratings and metamaterials, have shown promise but remain limited due to their polarization and wavelength sensitivity, complex design constraints, and poor performance under oblique illumination.

The new diffractive unidirectional light focusing system developed by UCLA researchers addresses these challenges through a different approach. By using deep learning to optimize the structures of a series of passive, isotropic diffractive layers, the team created a compact and broadband optical system that efficiently focuses light in the forward direction while suppressing light focusing in the reverse direction. This design is inherently polarization-insensitive and scalable across multiple wavelengths, enabling consistent unidirectional light control over a broad spectral range. Unlike traditional methods that rely on complex materials or nonlinear optical effects, this deep learning-based optimized 3D structure achieves asymmetric light propagation using passive, isotropic diffractive layers, eliminating the need for active modulation or high-power sources.

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The UCLA research team demonstrated the effectiveness of their system using terahertz (THz) radiation. Using a 3D printer, they fabricated a two-layer diffractive structure that successfully focused the THz radiation in the forward direction while blocking backward-propagating energy. This experimental validation confirmed the system's practical capability for all-optical, passive control of unidirectional light propagation.

By enabling directional control of light without relying on active modulation, nonlinear materials or high-power sources, this technology can be used to enhance the efficiency and security of free-space optical links, particularly under dynamic or noisy conditions. Furthermore, the compact and passive nature of the system makes it ideal for integration into advanced imaging and sensing platforms, where directional light control can enhance signal clarity and reduce background interference in complex or cluttered settings. By suppressing unwanted back-reflections, this technology can also be used to enhance the stability and performance of a wide range of optical systems—including laser machining platforms, biomedical instruments, and precision metrology setups—where the reflected light can otherwise introduce noise, reduce accuracy, or damage sensitive components.

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The study was supported by the US National Science Foundation (NSF). The co-authors of this publication include graduate students Y. Li, T. Gan, J. Li as well as Professors M. Jarrahi and A. Ozcan, all from UCLA.

Original paper: https://advanced.onlinelibrary.wiley.com/doi/full/10.1002/adom.202403371