A laser beam hits the polished tip of a special optical fiber. The fiber contains seven tiny light channels and a barely visible nanostructure on its surface. Light arriving from different directions is guided into different cores, like an optical sorter that recognizes each angle of incidence.

This process is a new approach in fiber optics, as it is a fiber tip that not only guides light, but also analyzes and distributes it depending on its direction of arrival. Researchers from the Fiber Photonics Department at the Leibniz Institute of Photonic Technology (Leibniz-IPHT) and the Competence Center for Specialty Fiber Optics (KSF) developed a method to separate light on the fiber tip according to its angle of incidence.

The result is a fiber-based angular demultiplexer that can collect light from almost any direction. This method could lead to more compact and energy-efficient optical sensors and communication systems.

A New Way to Steer Light

The concept combines a multicore fiber with a nanoprinted structure. On the end face of a fiber containing seven individually addressable light channels, the researchers printed a ring-shaped nanostructure. This structure directs incoming light into different cores depending on its angle of incidence. Thus, the fiber tip itself becomes a sensor that can determine the source of the light.

“We found a way to guide light precisely into the appropriate core,” explains lead author Dr. Oleh Yermakov. “This allows us to determine the direction of a light beam directly at the fiber tip with an efficiency that has not been achieved before.”

A High-Precision Specialty Fiber

The required fiber was developed at the Competence Center for Specialty Fiber Optics. The team led by Adrian Lorenz fabricated the multicore fiber that serves as the platform for the nanostructure.

“Our fiber forms the foundation on which the optical design is based,” says engineer Adrian Lorenz. “It contains several light channels that are arranged so each one can be addressed individually.”

The result is a compact, robust system that collects light from many directions and sorts it by angle directly within the fiber.

An Antenna for Light

Remarkably, the system functions not only as an angle detector, but also as a highly efficient light collector. It can capture light over a wide range of angles and distribute it evenly among the fiber cores, even at angles of up to 80 degrees, where conventional optical fibers typically couple very little light.

Antenna for Biophotonic Measurements

“Our structure works like an antenna for light,” says Yermakov. “It can capture signals from many directions and guide them selectively. This makes it particularly interesting for applications where light sources cannot be precisely aligned, such as environmental monitoring or biophotonic measurements.”

The concept could also open new possibilities in optical communications. Because the structure responds differently to different angles of incidence, it enables optical signals to be separated, combined, or analyzed in novel ways. These capabilities could be valuable in future optical networks or sensing technologies.

New Perspectives for Sensing and Communication

This study is the first to demonstrate experimentally that a structure integrated directly onto a fiber can detect and separate not only the intensity of light, but also its angle of incidence. The achieved efficiency significantly exceeds that of conventional systems.

This opens new possibilities for photonic sensing, communication technologies, and environmental analysis.

“In the long term, such structures could help make optical sensors and communication systems more compact and energy-efficient,” says Professor Markus Schmidt. “They demonstrate the potential of modern optical fibers, which extends far beyond their traditional role as simple light guides.”

Publication: Fiber-based angular demultiplexer using nanoprinted periodic structures on singlemode multicore fibers. Yermakov, O., Zeisberger, M., Schneidewind, H. et al. Nat Commun 16, 2294 (2025). https://doi.org/10.1038/s41467-025-57440-2