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Engineering of Tunable Topological Texture Transformation in Optical Skyrmions and Bimerons using Enantiomeric Excess

This paper proposes and experimentally demonstrates a tunable, cost-effective method for dynamically transforming optical skyrmions and bimerons into various topological states (such as Bloch or Néel) by controlling the enantiomeric excess of chiral media, thereby enabling robust manipulation of polarization textures for applications in information processing and particle manipulation.

Original authors: Ankita Karmakar, Abhishek Mandal, Maruthi M. Brundavanam

Published 2026-06-16

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Ankita Karmakar, Abhishek Mandal, Maruthi M. Brundavanam

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Idea: Shaping Light Like Play-Dough

Imagine light not just as a beam that turns things on and off, but as a complex, twisting ribbon with a specific "twist" or pattern. Scientists call these patterns optical skyrmions. Think of them like tiny, invisible tornadoes made of light that are incredibly stable; if you push them or shake them, they don't fall apart easily.

The researchers in this paper found a clever, low-cost way to change the shape of these light tornadoes on demand. Instead of building a complicated machine with many moving parts to reshape the light, they simply passed the light through a special liquid. By changing the "recipe" of that liquid, they could instantly transform the light from one shape to another.

The Key Ingredients

To understand how they did this, let's look at the three main ingredients:

The Light (Vector Vortex Beams):
Imagine a flashlight beam, but instead of just shining straight, the light is spinning like a corkscrew. The researchers created a beam that is a mix of two different spinning lights. This mix creates a complex pattern called a "skyrmion."
The Liquid (Chiral Media):
The team used a liquid containing enantiomers. These are molecules that are like mirror images of each other—think of your left hand and your right hand. They look the same but are opposite.
- Enantiomeric Excess (EE): This is the paper's "magic knob." It simply means: How much more of the "left-handed" molecules are there compared to the "right-handed" ones?
- If you have 50% left and 50% right, they cancel each other out (like a neutral mixture).
- If you have more of one type, the liquid becomes "chiral" (handed).
The Magic Trick (Optical Rotation):
When the spinning light beam passes through this liquid, the liquid acts like a slow-motion turntable. Depending on whether there are more "left" or "right" molecules in the mix, the liquid twists the light's polarization (its direction of spin) by a specific amount.
- The Analogy: Imagine the light beam is a dancer spinning in a circle. The liquid is a wind that blows on the dancer. If the wind blows harder from the left, the dancer spins one way; if it blows harder from the right, they spin the other way. By adjusting the wind (the EE), the researchers can stop the dancer, make them spin faster, or change their dance style entirely.

What They Achieved

The researchers demonstrated that by simply changing the ratio of the mirror-image molecules in the liquid, they could switch the light's pattern between different "styles":

Bloch-type: Imagine a hedgehog where the spikes point straight out from the center.
Neel-type: Imagine a hedgehog where the spikes point sideways, circling the center.
Intermediate States: They could also create any shape in between these two extremes.

They didn't need to move lenses or use complex computers to do this. They just changed the liquid's composition, and the light transformed instantly.

The "Bimeron" Extension

The paper also showed they could create a more complex shape called a bimeron.

Analogy: If a skyrmion is one single tornado, a bimeron is like two half-tornadoes stuck together back-to-back.
Just like with the single tornado, they could use the liquid to twist and reshape these double-tornadoes into different patterns.

Why This Matters (According to the Paper)

The paper claims this method is:

Stable: The light patterns stay strong and don't break easily, even when changing shapes.
Simple and Cheap: It avoids the need for expensive, complex optical setups.
Versatile: It works for simple shapes and more complex, higher-order shapes.

The researchers suggest this could be useful for optical communication (sending data with light) and particle manipulation (using light to move tiny objects), as it allows for flexible control over these light patterns without rebuilding the whole system.

Summary

In short, the team built a system where light acts like a shape-shifter. By mixing mirror-image molecules in a liquid, they created a "dial" that lets them twist the light into any desired topological shape (like a Bloch or Neel skyrmion) instantly, proving that light can be engineered efficiently for future information technologies.

Technical Summary: Engineering of Tunable Topological Texture Transformation in Optical Skyrmions and Bimerons using Enantiomeric Excess

Problem Statement
Optical skyrmions, topologically protected quasiparticles characterized by nontrivial polarization textures, hold significant promise for applications in optical communication, data storage, and particle manipulation. While the generation of optical skyrmions has advanced, a critical challenge remains: achieving dynamic, controllable, and on-demand transformation between different topological textures (specifically Bloch, Néel, and intermediate states) within a stable experimental platform. Existing methods often rely on static generation, complex optical architectures, or modifications requiring spatial light modulators and digital holography, which limit adaptability for reconfigurable photonic applications. Furthermore, the ability to dynamically tune these textures while preserving topological protection, and to extend such control to generalized textures like optical bimerons, remains largely unexplored.

Methodology
The authors propose and experimentally demonstrate a common-path, efficient methodology for the dynamic transformation of Stokes' skyrmionic textures. The core mechanism leverages the enantiomeric excess (EE) of an optically active (OA) material to control the relative phase between orthogonal polarization components of structured vector vortex beams (VVBs).

Beam Generation: Vector vortex beams are generated by superimposing a Gaussian beam and a vortex beam with orthogonal circular polarizations using a phase-only spatial light modulator (POSLM) and waveplates.
Tuning Mechanism: The VVBs interact with a solution of chiral enantiomers (specifically (+)- and (-)-limonene). The EE of the mixture, defined as the excess of one enantiomer over the other, induces a specific optical rotation (OR). This rotation introduces a controllable phase difference ( $\gamma_{OA}$ ) between the left-handed (LCP) and right-handed (RCP) circular components.
Transformation Logic: By varying the EE from -100% to +100%, the relative phase $\gamma_{OA}$ is tuned. This phase shift alters the azimuthal phase variation $\alpha(\theta)$ of the polarization field, thereby transforming the skyrmionic texture from Bloch-type to Néel-type or to any intermediate state without altering the optical path or requiring additional complex holographic elements.
Extension to Bimerons: The methodology is extended to optical bimerons (quasiparticles composed of two half-skyrmions) by passing the VVBs through a birefringent quarter-wave plate (QWP) to convert the circular basis to a linear basis, followed by the same EE-controlled interaction.

Key Contributions and Results

Dynamic Texture Control: The experiment successfully demonstrated the on-demand conversion of optical skyrmions between Bloch-type (hedgehog-like or vortex-core structures depending on definition context in the paper) and Néel-type textures.
- An EE of $\pm 100\%$ yielded a Bloch-type texture.
- An EE of $\pm 50\%$ yielded a Néel-type texture.
- A racemic mixture (0% EE) resulted in no net phase shift, preserving the initial Bloch-type state.
- Intermediate EE values allowed for the generation of arbitrary intermediate topological states.
Topological Robustness: The skyrmion number ( $S$ ) was calculated for each transformed state. The results confirmed that the skyrmion number remained conserved (integer values) throughout the dynamic transformations, proving the topological robustness of the method even as the texture geometry changed.
Generalization to Higher Orders: The tunable transformation scheme was successfully applied to second-order skyrmions and bimerons, demonstrating that the method is not limited to first-order topological charges.
Bimeron Manipulation: The study showed that optical bimerons could also be dynamically transformed between Bloch and Néel types by controlling the EE, maintaining the topological integrity of the bimeron structure.
Theoretical Framework: The authors introduced the concept of a "Generalized Skyrmion Torus" to visualize these transformations. In this model, the toroidal angle ( $\gamma$ ) represents the texture type (Bloch, Néel, intermediate), while the polar angle ( $\phi$ ) distinguishes between skyrmions, anti-skyrmions, and bimerons. The EE acts as the control parameter to navigate this torus.

Significance and Claims
The paper claims that this approach offers a stable, flexible, and cost-effective alternative to existing complex holographic or interferometric methods for manipulating topological textures. By utilizing the intrinsic chiral response of optically active materials, the method eliminates the need for complex optical geometry modifications or multiple waveplate configurations.

The authors assert that this work provides a versatile platform for the dynamic engineering of generalized optical quasiparticles. The preservation of topological protection during transformation highlights the potential for robust applications in optical communication, quantum information processing, and particle manipulation. The ability to switch between distinct topological states (Bloch/Néel) and generalized states (bimerons) on a single, common-path setup represents a significant step toward practical, reconfigurable topological photonic devices. The work does not claim to solve all challenges in the field but establishes a specific, tunable mechanism for texture transformation that is robust against perturbations and applicable to higher-order structures.