Metafiber, a fully fiber-integrated device, uses a 3D nanoprinted phase-only hologram on a dual-core fiber end face to enable remote focus control by adjusting the relative power between guided modes.

The hologram encodes interference patterns from the two cores, allowing the focal spot to shift without moving parts and achieving continuous focus modulation over more than three microns with high beam quality.

A figure demonstrates the principle and shows a focus shift greater than 3 micrometers achieved by varying the relative power between the two cores.

The study highlights on-fiber photonic integration and points toward pathways for next-generation fiber-based optical systems.

The approach is compact, robust, and fast, with tunability driven by power modulation rather than mechanical or liquid-crystal methods, and it remains compatible with existing fiber platforms.

Potential applications span high-speed optical trapping, integrated endoscopic tools for diagnostics or surgery, and improved signal routing in fiber communications.