French researchers have developed a spiral-shaped lens that maintains clear focus at different distances in varying light conditions. The new lens works much like progressive lenses used for vision correction but without the distortions typically seen with those lenses. It could help advance contact lens techno­logies, intra­ocular implants for cataracts and minia­turized imaging systems. “Unlike existing multifocal lenses, our lens performs well under a wide range of light conditions and maintains multi­focality regardless of the size of the pupil,” said Bertrand Simon from Photonics, Numerical and Nano­sciences Laboratory (LP2N), a joint research unit between the Institut d'Optique Graduate School, the University of Bordeaux and the CNRS in France. “For potential implant users or people with age-related farsightedn­ess, it could provide consistently clear vision, potentially revo­lutionizing ophthal­mology.”

The researchers call the lens a spiral diopter. Its spiraling features are arranged in a way that creates many separate points of focus – much like having multiple lenses in one. This makes it possible to see clearly at various distances. “In addition to ophthal­mology appli­cations, the simple design of this lens could greatly benefit compact imaging systems,” said Simon. “It would streamline the design and function of these systems while also offering a way to accomplish imaging at various depths without additional optical elements. These capa­bilities, coupled with the lens's multifocal properties, offer a powerful tool for depth perception in advanced imaging applications”

The inspiration for the spiral lens design came when Laurent Galinier from SPIRAL SAS in France was analyzing the optical properties of severe corneal defor­mations in patients. This led him to conceptua­lize a lens with a unique spiral design that causes light to spin, like water going down a drain. This phenomenon – an optical vortex – creates multiple clear focus points, which allow the lens to provide clear focus at different distances. “Creating an optical vortex usually requires multiple optical components,” said Galinier. “Our lens, however, incor­porates the elements necessary to make an optical vortex directly into its surface. Creating optical vortices is a thriving field of research, but our method simplifies the process, marking a significant advancement in the field of optics.”

The researchers created the lens by using advanced digital machining to mold the unique spiral design with high precision. They then validated the lens by using it to image a digital ‘E,’ much like those used on an optometrist's light-up board. The scientists observed that the image quality remained satis­factory regardless of the aperture size used. They also discovered that the optical vortices could be modified by adjusting the topo­logical charge, which is essentially the number of windings around the optical axis. Volunteers using the lenses also reported noticeable improvements in visual acuity at a variety of distances and lighting conditions.

Bringing the new lens to fruition required combining the intuitively crafted design with advanced fabri­cation techniques through a cross-disciplinary colla­boration. “The spiral diopter lens, first conceived by an intuitive inventor, was scientifi­cally substantiated through an intensive research colla­boration with optical scientists,” said Simon. “The result was an innovative approach to creating advanced lenses.”

The researchers are now working to better understand the unique optical vortices produced by their lens. They also plan to perform systematic trials of the lens’ ability to correct vision in people to comprehensively establish its performance and advantages in real-world conditions. In addition, they are exploring the possi­bility of applying the concept to prescription eyeglasses, which could potentially offer users clear vision across multiple distances. “This new lens could signi­ficantly improve people’s depth of vision under changing lighting conditions,” said Simon. “Future developments with this technology might also lead to advance­ments in compact imaging techno­logies, wearable devices and remote sensing systems for drones or self-driving cars, which could make them more reliable and efficient.” (Source: Optica)

Reference: L. Galinier et al.: Spiral Diopter: Freeform Lenses With Enhanced Multifocal Behavior,” Optica 11, 2 (2023); DOI: 10.1364/OPTICA.507066

Link: Photonics, Numerical and Nanosciences Laboratory (LP2N),  Institut d’Optique d’Aquitaine, Talence, France