Light Cage Revolution: Chiba University Researchers Develop Flat-Lens Technology to Create Nondiffracting "Optical Bottle" Beams

Researchers develop a flat-lens method to create "light cages" for particle trapping. Learn how this Bessel beam technology improves imaging and laser precision.

By: AXL Media

Published: Apr 2, 2026, 7:26 AM EDT

Source: The information in this article was sourced from EurekAlert

Overcoming the Divergence of Traditional Lasers

Standard laser sources typically produce Gaussian beams, which naturally diverge and spread out as they travel. This physical limitation has long hindered applications that require light to remain concentrated over significant distances. While "structured light" beams like Bessel beams offer a solution due to their self-interfering, nondiffracting nature, they often possess complex ring structures that make them difficult to use in practical settings. Furthermore, generating advanced shapes like "optical bottle beams" has historically required expensive, bulky, and perfectly aligned optical setups.

The "Light Cage" Breakthrough

A research team led by Assistant Professor Andra Naresh Kumar Reddy at Chiba University’s Molecular Chirality Research Center has successfully simplified this process. Their new method transforms a standard Gaussian beam into a modified zero-order Bessel beam using a binary axicon. This beam is then passed through a flat multilevel diffractive lens (MDL)—a thin, concentric-ringed lens only microns in height. The MDL reshapes the light into an "optical bottle beam," characterized by a series of dark regions entirely surrounded by bright light. This creates a functional "light cage" in free space, ideal for the non-invasive trapping and manipulation of microscopic particles and atoms.

Precision Engineering and Self-Healing Light

The magic of the discovery lies in the MDL’s design. Composed of concentric rings with widths of 7 $\mu m$ and varying heights, the lens uses an inverse-design approach to control longitudinal interference. As the beam propagates, it forms alternating bright and dark regions that remain invariant over long distances. Crucially, these beams demonstrate "self-healing" characteristics, meaning they can reform their shape even after encountering obstacles. This stability begins at a working distance of approximately 20 cm from the lens and persists through free space, offering a level of control previously unattainable in such a compact form factor.