WASHINGTON — Researchers have created a special flat lens that shapes light into an optical needle — a thin beam that stays tightly focused over a long distance. Combining this lens, which is about 7 microns thick, with optical coherence tomography (OCT) could allow imaging that reaches deeper into tissue while maintaining a sharp focus.
OCT, which is commonly used in ophthalmology, uses light to provide high-resolution 3D images without requiring any contrast agents or labels.
“Although OCT can image structures at different depths, it has a harder time capturing very fine details on the tissue surface,” said research team leader Haowen Liang from Sun Yat-sen University in China. “With the optical needle, it’s possible to get clear, high-resolution images both across the tissue surface and deep inside it at the same time, which could help reveal details that are difficult to see with conventional systems.”
In the Optica Publishing Group journal Optics Letters , the researchers describe their new ultrathin multi-level diffractive lens, which uses tiny microstructures to create an optical needle. They show that replacing the conventional focusing lens in an OCT system with the new lens increased imaging depth by a factor of nine without requiring a complicated optical redesign.
“The new lens could help doctors see deeper and more clearly inside the eye, leading to earlier disease detection and better diagnosis,” said Liang. “In the longer term, the same technology could be used in everyday devices such as smartphone cameras, enabling smaller, simpler and lower-cost imaging systems without sacrificing performance.”
Creating a needle of light
For the new work, the investigators were interested in improving OCT performance without making the system bigger, more complicated or more expensive. With traditional optics, better performance often comes at the cost of increased size and complexity. So instead of using traditional optics, they designed an extremely thin multi-level diffractive lens made from millions of microscopic step-like structures, each only a fraction of the thickness of a human hair.
Using diffractive microstructures to manipulate the light makes it possible to combine several optical functions into a single device, helping keep the system compact, simple and cost-effective. It also provided the extra level of control needed to create an optical needle that is both extremely narrow and exceptionally long.
“Advances in computational design provided powerful optimization tools for shaping the optical needle needed for OCT, while recent progress in 3D laser writing enabled these complex structures to be fabricated with exceptional precision,” said Liang. “Together, these advances made it possible to control light at the subwavelength scale and turn sophisticated optical designs into practical devices.”
Deeper imaging with a tiny lens
The researchers fabricated multi-level diffractive lenses and showed that they could focus broadband light in the wavelength range of 800 to 900 nm into an optical needle with an average lateral focal width of 2.4 μm and a longitudinal focal depth of 2640 μm, achieving a depth-to-width ratio of 1100:1.
They then integrated one of the lenses into a spectral-domain optical coherence tomography (SD-OCT) system and compared it with an SD-OCT system using a conventional objective lens with a similar lateral resolution. The multi-level diffractive lenses extended imaging depth nearly nine times compared to the traditional approach.
“What's exciting is the performance gain we get from such a simple change,” said Liang. “With a straightforward lens replacement, we were able to image much deeper into tissue while still maintaining high resolution. That's very difficult to achieve with conventional optical designs.”
Now that the researchers have demonstrated the concept, they are working to make the optical needle dynamically tunable so that the shape and intensity profile could be adjusted for various imaging conditions. They also want to use the optical needle to create much simpler optical architectures for high-performance imaging systems used in consumer devices.
Paper : J. Huang, Z. Duan, P. Xiao, H. Liang, “Optical Needle with Narrow Lateral Focal Width and Extended Longitudinal Focal Depth Enabled by Multi-Level Diffractive Lens,” Opt. Lett. , 51
Experimental study
Not applicable
7-Jul-2026