Acoustic Control of Optical Angular Momentum and Helicity at Gigahertz Frequencies

Controlling the fundamental properties of light, such as its angular momentum and helicity, usually relies on static optical elements or complex photonic structures. Two recent studies from the CReA Control of Elementary Excitations by Acoustic Fields demonstrate an alternative approach: using engineered gigahertz acoustic fields to dynamically manipulate optical degrees of freedom in solid-state platforms.

In the first study¹, published in Nature Communications (August 2025), the authors demonstrate that acoustic vortices generated in bulk acoustic wave resonators can transfer orbital angular momentum (OAM) to light. By engineering the geometry of piezoelectric transducers, they generate acoustic waves with helical phase fronts at GHz frequencies. These acoustic vortices possess well-defined topological charges (ℓ = 1 to 13 and beyond) tunable by adjusting the excitation frequency and device geometry. Through acousto-optic coupling, the helical acoustic phase fronts impart orbital angular momentum to reflected optical beams, enabling gigahertz-rate modulation of optical OAM without modifying the optical path itself. This work establishes a solid-state route for generating and tuning structured light using mechanical excitations.

The second study², published in Scientific Reports (November 2025), builds on this concept by moving toward laterally confined, chip-compatible architectures. Here, the authors demonstrate that helical “drum” modes (acoustic modes confined both vertically and laterally in piezoelectric resonators) can be used to modulate the helicity of light at gigahertz frequencies. By exciting sector-shaped electrodes with controlled phase delays, they generate confined acoustic modes carrying angular momentum with selectable handedness. Interferometric surface measurements and numerical modeling confirm the helical character of these modes and their ability to induce controlled phase and helicity modulation in reflected optical fields.

Taken together, these two studies establish a coherent experimental framework for acoustic control of light’s angular momentum across different device scales. The Nature Communications paper demonstrates the fundamental principle and electrical tunability of OAM transfer using bulk acoustic vortices, while the Scientific Reports paper advances the concept toward integrated, lithographically compatible devices with laterally confined acoustic drum modes capable of selectable helical handedness. Both approaches rely on the same core idea: that engineered acoustic fields can act as active, dynamically tunable elements for shaping optical excitations.

This work positions gigahertz acoustics as a powerful tool for acousto-optical control, enabling time-varying modulation of optical angular momentum at unprecedented frequencies. Despite current limitations in optical phase modulation depth, the approach shows potential relevance for structured light sources, chiral photonics, optical communication schemes employing OAM-based encoding, and hybrid quantum-acoustic systems. More broadly, it highlights how elementary excitations—here, phonons with designed angular momentum—can be harnessed to control other quasiparticles in solid-state platforms.

¹Title: GHz acousto-optic angular momentum with tunable topological charge
Authors: A. Pitanti, N. Ashurbekov, I. de Pedro Embid, M. Msall, P. V. Santos
Source: Nat. Commun., 16, 8116 (2025)
DOI: 10.1038/s41467-025-63362-w

²Title: Method for GHz optical helicity modulation by acoustic drum modes on a chip
Authors: N. Ashurbekov, I. de Pedro Embid, A. Pitanti, M. Msall, P. V. Santos
Source: Sci. Rep., 15, (2025)
DOI: 10.1038/s41598-025-26587-9 

CReA: Control of Elementary Excitations by Acoustic Fields