Engineers have devised a new way to steer light using a tiny 3D hologram printed on the end of a fiber. This innovation removes bulky equipment. It works by modulating the relative power between two cores in a dual-core optical fiber.

Precise control of light focus is essential for tasks such as microscopy, laser surgery, quantum optics and telecommunication. Traditional systems rely on moving parts or liquid crystals that slow focus changes and limit integration. They are also large, making miniaturization difficult.

Researchers from the Leibniz Institute of Photonic Technology and Friedrich Schiller University in Germany created a device called the tunable Metafiber. They nanoprinted a phase-only hologram directly on the end face of a dual-core fiber. The hologram responds to interference patterns created by the two guided modes.

By adjusting power in the two cores, the engineers can shift the focal spot by more than three microns without moving any parts. Experiments showed continuous and precise focus control while maintaining high beam quality. This ability is crucial for remote, on ‑fiber control.

The Metafiber’s tuning happens entirely through power modulation. It avoids mechanical components and liquid-crystal switches, making it faster and more robust. Because the hologram is inside the fiber, it integrates into compact photonic systems. This reduces size and increases reliability.

High-speed optical trapping is one potential use. In optical tweezers, scientists move tiny particles or biological cells with light. Rapid focus changes allow them to capture and release objects quickly. The Metafiber’s precise control could improve these tools.

Minimally invasive medical devices may benefit. Engineers could incorporate the Metafiber into endoscopic tools that focus light inside the body for surgery or diagnostics. Doctors could steer light to specific tissues without moving mechanical lenses.

Telecommunications systems could also use the device. Fiber networks carry data across long distances. Fine control of light inside fiber could improve signal routing and reduce losses. It might enable reconfigurable photonic circuits for future communications.

Current fiber systems often use external lenses to adjust focus. Those assemblies add size and alignment challenges. The Metafiber eliminates the need for external components. It uses the fiber itself as both waveguide and focusing element.

The researchers emphasize that the Metafiber is compatible with existing fiber fabrication. They designed the hologram with nanometer precision and printed it using a high‑resolution 3D printer. The resulting structure remains stable during operation.

The dual-core fiber is central to the design. Each core guides light separately. By sending more power through one core, interference patterns shift and move the focal spot. The hologram converts these patterns into a controlled beam.

Testing demonstrated smooth focus shifts over a range of more than three micrometers. This scale is significant for microscale optical devices. The beam quality remained high, meaning the focus stayed sharp.

This innovation shows how engineers can build tunable optical devices inside fiber. It expands the toolkit for integrated photonics. Integrated devices reduce cost and complexity and open new possibilities in sensing and computing.

The ability to control both the angle and position of a beam inside fiber may influence fields beyond optics. For example, researchers may design fiber-based quantum circuits or chips that harness light–matter interactions for computing.

The device is still a prototype. Future work might extend the focus range, integrate more complex holograms or combine the Metafiber with other on‑fiber components like gratings and filters. Engineers may also explore different materials or fiber geometries.

Light control is central to quantum optics experiments. Researchers use pulses of light to manipulate atoms and molecules. Being able to tune focus quickly improves experiment timing and accuracy.

The technology may also support new types of sensors. For example, fiber-based sensors that measure temperature, strain or chemical composition often rely on interference patterns. By shifting the focus, the device can adjust sensitivity or calibrate measurements.

Smart manufacturing could incorporate the Metafiber for material processing. Laser systems cut, weld and etch materials. A fiber with tunable focus reduces the need for complex lens assemblies, making systems cheaper and easier to maintain.

Because the Metafiber uses a phase-only hologram, it wastes very little power. Efficient light control is important for low-power devices and portable instruments.

This research underscores how combining disciplines yields innovation. Photonics, materials science, nanotechnology and engineering converged to create the Metafiber. The progress reminds us that even small components can have big impacts when designed with care and creativity.

References: ScienceDaily article “Tiny hologram inside a fiber lets scientists control light with incredible precision,” August 27, 2025.