A New Multicore Fiber With a Nanoprinted Hologram Enables Precise Control of the Light Focus – Without Any Moving Parts

A green dot of light moves, yet nothing mechanical changes. No lens shifts and no mirror tilts. The movement is created solely by light, guided by a tiny structure at the tip of a glass fiber. Researchers at Leibniz IPHT have developed a fiber whose focus can be adjusted purely optically. This is made possible by a nano-printed holographic structure at the tip of a multicore fiber.

Controlling Focus Through Light Alone

“We show for the first time that the focusing properties of light can be controlled solely by selectively exciting individual fiber modes,” says Mohammad-Hossein Khosravi, first author of the study published in 2025 in Nature Communications.

On the end face of a fiber containing 37 individually addressable light channels, the researchers printed a microscopic holographic phase element. This hologram modifies the phase of the outgoing light such that each channel generates its own focal point in space. By selectively coupling light into different cores, the focal position can be shifted freely – enabling remote focusing without any moving optics.

A Multicore Fiber for Holographic Applications

The fiber itself was developed at the Competence Center for Optical Fiber Technology (KSF) at the Leibniz-IPHT. For the first time, researchers combined a high-density multicore fiber—featuring identical, fully decoupled cores for visible light – with a nanoprinted hologram on its tip. “Each core carries its own light signal without interference from neighboring channels,” explains Adrian Lorenz from KSF. “This is essential for addressing the holographic pattern with precision.” The multicore fiber contains 37 identical light-guiding channels arranged in a compact hexagonal structure. It was fabricated using a stack-anddraw process with such precision that the individual cores remain optically isolated. This level of control forms the basis for the holographic manipulation of light at the fiber tip.

A New Tool at the Interface of Fiber Technology and Nanophotonics

The hologram was designed using a computational optimization approach based on an extended version of the Gerchberg – Saxton algorithm. The result is a phase-only hologram that precisely shapes the light distribution and allows the focal point to be shifted electronically. “With this structure, we can effectively compute – not with electrons, but with light,” says Markus Schmidt.

“The fiber tip itself becomes a programmable optical surface.” “This work demonstrates how photonic design and fiber technology can be combined into a new integrated platform,” Schmidt adds. “The fiber tip no longer just guides light – it becomes an active optical component.”

From Communications to Surgery

The focal point can be repositioned within milliseconds, entirely without mechanical motion. Control is achieved solely through the distribution of light at the fiber input – and remains stable even when the fiber is slightly bent. In biophotonics, such fibers could enable optical manipulation inside living cells or guide laser light precisely within tissue during surgery. In micromachining, laser beams could be steered with micrometer accuracy, while in telecommunications, optical signals could be directed and multiplexed with high precision. “This study is a key milestone for us,” says Markus Schmidt. “It shows how nanophotonics and fiber technology are converging – and how optical fibers are evolving into active, controllable tools.”

Original Publication: https://doi.org/10.1038/s41467-024-55805-7