Light is traditionally described by properties such as wavelength, amplitude, phase, and polarization. Advances in optics have shown that light can also be shaped into complex spatial patterns known as structured light, enabling new ways to carry information and interact with matter for applications in imaging, optical communications, and information processing.
Generating structured light at different wavelengths remains challenging using conventional optical methods. Nonlinear optics and metasurfaces offer a promising solution by enabling precise control of light at the nanoscale. However, designing metasurfaces that operate efficiently across both fundamental and harmonic frequencies remains difficult, and material absorption can reduce conversion efficiency.
A recent study made available online on May 18, 2026 and will be published in Volume 18, Issue 04 of the IEEE Photonics Journal on August 1, 2026, explores the newly introduced concept of topology imprinting in nonlinear metasurfaces as a new paradigm for nonlinear wavefront engineering. "In topology imprinting, the spatial topology of an optical field at the fundamental frequency is directly transferred to the generated harmonic radiation, offering a new way for generating structured light while overcoming material and nanofabrication constraints," explains Dr. Natalia M. Litchinitser. The study was also featured in the JSTQE Special Issue on Photonics for Climate Change Mitigation and Adaptation, highlighting advances in photonic technologies relevant to addressing today's climate challenges.
The review discusses the physical mechanisms underlying topology imprinting and highlights key experimental demonstrations. The concept has been experimentally realized using all-dielectric metasurfaces composed of subwavelength resonators. Various structured optical fields have been generated and preserved using this approach, including optical vortex beams carrying orbital angular momentum and optical Hopf links. A notable demonstration is the third-harmonic generation of vortex beams that preserve the spatial topology of the fundamental beam, an ability that is difficult to achieve using conventional approaches.
The study also discusses current challenges, including the relatively low efficiency of nonlinear frequency conversion in ultrathin metasurfaces, limitations imposed by available nonlinear materials, and the difficulties associated with scaling and integrating into on-chip photonic platforms. Looking ahead, the authors identify several promising research directions, including the development of low-loss, highly nonlinear materials, the incorporation of active and tunable functionalities into metasurface designs, and the use of machine learning to optimize device performance.
"Nonlinear topology imprinting can pave the way towards compact photonic platforms capable of generating complex structured light fields, and can impact a wide range of fields, including holography, optical communications, quantum photonics, and advanced imaging systems," remarks Dr. Litchinitser.
Overall, the review highlights topology imprinting as a promising strategy for generating and manipulating complex optical fields while preserving their unique structures across different wavelengths, paving the way for compact next-generation photonic technologies.
