Lens Extends Focal Length, Depth of Vision as Conditions Change

A new, spiral-shaped lens could make consistently clear vision possible for people with lens implants or age-related farsightedness. The spiral diopter works similarly to progressive lenses used for vision correction, while foregoing the often-found distortions. Its spiral shape creates many separate points of focus, allowing the user to see clearly at different distances and in various light conditions.

In addition to advancing contact lens technologies and intraocular implants for cataracts, the spiral diopter lens could be used to miniaturize imaging systems while maintaining their optical quality.

According to the researchers, the spiral diopter lenses are superior to conventional trifocal lenses at larger apertures for most focal points, while preserving multifocal behavior even at smaller apertures. They provide wider depth perception while reducing the reliance on larger apertures.

Researchers have developed a lens that uses a spiral-shaped surface to maintain a clear focus at different distances in varying light conditions. Courtesy of Laurent Galinier.

“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, a researcher from the Photonics, Numerical, and Nanosciences Laboratory (LP2N), a joint research unit between the Institut d'Optique Graduate School, the University of Bordeaux, and the Centre National de la Recherche Scientifique (CNRS). “This new lens could significantly improve people’s depth of vision under changing lighting conditions.”

The inspiration for the spiral lens design emerged when the paper’s first author, 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, known as 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,” Galinier said. “Our lens, however, incorporates the elements necessary to make an optical vortex directly into its surface.”

The lens uses the spiral properties of one of its diopters to create optical vortices. The freeform design of the lens allows its focal points to be shaped from a few simple parameters on the diopter geometry. This enables multifocality, extended depth of field, and depth encoding through the shapes of the focal spots, independent of the aperture.

The researchers created the lens by using digital machining to precisely mold the spiral design. They tested the lens by using it to image a digital “E,” similar to the letters used on an optometrist’s light-up board. They observed that the image quality remained satisfactory regardless of the aperture size. 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.

Subjects who volunteered to wear the lenses reported improvements in visual acuity at a variety of distances and under different lighting conditions.

The new lens could be used on contact lenses (shown), in intraocular implants for cataracts, and to create new types of miniaturized imaging systems. Courtesy of Laurent Galinier.

The spiral lens could also lead to new approaches in wearable optics and ultracompact embedded imaging systems.

“In addition to ophthalmology applications, the simple design of this lens could greatly benefit compact imaging systems,” Simon said. “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’ multifocal properties, offer a powerful tool for depth perception in advanced imaging applications.”

The design and fabrication of the spiral diopter lens was made possible 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,” Simon said. “The result was an innovative approach to creating advanced lenses.”

To further enhance overall performance of the lens, the researchers are investigating the behavior of the optical vortices and the response of the vortices to different aberrations. They also plan to perform systematic trials of the lens’ ability to correct vision in people to evaluate the performance of the lens in real-world conditions. In addition, they are exploring the possibility of applying the concept of the spiral lens to prescription eyeglasses to enable clear vision across different distances.

Further development of the technology could also lead to advancements in compact imaging technologies, wearable devices, and remote sensing systems for more efficient drones and self-driving cars.

The research was published in Optica (www.doi.org/10.1364/OPTICA.507066).