A three-dimensional acousto-optic deflector (2510.07633v1)

Abstract: Acousto-optic deflectors (AODs) are widely used across physics, microscopy, neuroscience, and laser engineering, providing fast, precise, and non-mechanical control of light. While conventional AODs naturally support multiplexing in one and two dimensions, no analogous device has existed for three-dimensional control, leaving a critical gap in rapid focus tuning and 3D beam shaping. Here we demonstrate a three-dimensional AOD system capable of multiplexed axial and lateral beam control with high speed and large dynamic range. We achieve this by combining a double-pass AOD with a diffraction grating in the Littrow configuration to realize a compact frequency-tunable lens with multiplexing capability. Our device enables axial scanning over more than twenty Rayleigh ranges with switching rates up to 100 kHz, while simultaneous multi-tone driving produces arbitrary multi-focal beam profiles. By integrating the axial module with lateral deflection, we generate reconfigurable 3D optical patterns. This approach establishes a broadly applicable platform for multiplexed 3D beam control, with potential applications from high-resolution microscopy and laser processing to scalable neutral-atom quantum technologies.

• The paper demonstrates a novel 3D acousto-optic deflector integrating a double-pass AOD and Littrow grating to achieve rapid, multiplexed focus control.
• It employs frequency-tuned axial scanning to reach over 22 Rayleigh ranges with sub-10 μs switching, balancing dynamic range with high speed.
• The design supports reconfigurable 5×5×3 spot arrays, offering significant advances for quantum assembly, volumetric microscopy, and laser processing.

Three-Dimensional Acousto-Optic Deflector: Multiplexed Fast 3D Beam Control

Introduction and Motivation

Acousto-optic deflectors (AODs) have become standard tools in applications requiring high-speed, non-mechanical laser beam steering and multiplexing, including advanced microscopy, quantum technologies, and laser processing. Conventional AOD systems natively support 1D or 2D multiplexed deflection, limited fundamentally by deflection geometry and the inability of simple AOD geometries to control axial (focus) position independently and rapidly. No previously demonstrated optical element provides full, fast, and reconfigurable 3D beam control with arbitrary multiplexing capability, which is a critical need in high-throughput quantum device initialization, volumetric microscopy, and scalable atom-by-atom assembly in neutral-atom arrays.

This work introduces a practically deployable architecture for a three-dimensional AOD system capable of high-speed and large-dynamic-range beam steering and multiplexed focus control. The design overcomes previous challenges by employing a double-pass AOD combined with a Littrow diffraction grating and downstream lateral AODs to yield a single, frequency-controlled focus-tunable element with arbitrary 3D multiplexing capability at sub-10 μs switching rates.

Optical Design and Focus Control Architecture

The central innovation is the implementation of axial scanning—or tunable focusing—by a double-pass AOD + cat's-eye relay, wherein a Littrow grating retroreflects the beam near the intermediate focus. The longitudinal path-length change depends on the lateral displacement imparted by the AOD deflection angle, such that tuning the RF frequency applied to the AOD directly tunes the round-trip optical path and, hence, the effective focus of the output beam. The system acts as a frequency-controlled lens with an effective focal length

$f = \frac{f_{CEL}}{2 \tan(\theta) \tan(\phi)}$

where $f_{CEL}$ is the cat's-eye lens focal length, $\theta$ is the Littrow angle, and $\phi$ is the AOD-induced deflection angle.

Crucially, double-passing the AOD ensures that the beam lateral position is invariant with focal adjustment: both passes produce opposite angular shifts, so as the focus moves the beam centroid remains stationary. After telescoping and delivery optics, this design readily integrates with a downstream pair of crossed lateral AODs providing $x$ and $y$ deflection, thus enabling arbitrary 3D positioning of each deflected spot.

Multiplexing for Multi-Focal Patterns

A key feature is multiplexed axial control: driving the AOD simultaneously with several RF frequencies yields multiple spatially overlapping beams each with independent axial offset. After filtering non-collinear terms generated in the double-pass, one realizes multi-plane or extended-depth illumination with straightforward software control of the input RF comb. In the planar dimensions, standard lateral AOD multiplexing enables formation of multi-spot or lattice patterns with independently addressable focus for each element.

Experimental Performance and Key Results

The prototype system employs a commercial wide-bandwidth AOD (AAOptolectronic DTSX-400-810.920, 7.5 mm aperture) and an f=35 mm cat's-eye relay. With a waist of 2 mm at the AOD and an 813 nm input beam, the device achieves:

• Axial scan range (focus tunability) exceeding 22 Rayleigh ranges for a single focal spot, with measured axial offsets up to 26.9 mm.
• Substantial tuning linearity: measured focus position vs. applied frequency is highly linear over the useful bandwidth.
• Multi-focal control: simultaneous three-tone drive produces three sharply resolved foci along $z$ with minimal cross-talk and amplitude balancing achievable via RF power adjustment.
• 3D reconfigurable arrays: By applying multi-tone drives on all three AODs, the authors demonstrate $5 \times 5 \times 3$ arrays of sharply focused spots, as well as arrays of "needle" beams created via axial multiplexing for depth-extended imaging or machining.
• Fast switching rates: The system supports rapid discrete focus jumps at rates up to 100 kHz, limited by acoustic transit times (rise time of 2 μs for a 2 mm input beam); even faster operation is possible by reducing the beam size or employing higher velocity AOD devices.
• Efficiency: Power transmission through the axial scanning device is measured at 46% (center frequency); a drop to $\sim$28% is observed at the extreme points of the scan range, primarily due to AOD diffraction efficiency variations over the bandwidth.

Systematic Considerations and Tradeoffs

Several key optical and systematics considerations were analyzed:

• Dynamic range vs. speed: Larger input beam waists at the AOD enable larger $z$-scan range relative to the focused waist, but increase the AOD's acoustic rise time, thereby reducing maximal switching speed.
• Aberrations and focus overlap: The double-pass design suppresses lateral beam shear during focus scanning, yielding $\leq 20$ μm focus shifts across the scan; remaining displacements and beam astigmatism are attributed to residual misalignments and cat's-eye lens imperfections.
• Frequency shifted multiplexing: Each multiplexed focus spot is frequency-shifted by the RF drive; interferences can occur at MHz frequencies where the beats are far above atomic dynamics timescales, making them negligible for applications like neutral-atom arrays.
• Device scaling: The architecture can be further miniaturized with custom mechanics; reducing the cat's-eye lens focal length by a factor of four would increase the scan range to $>100 z_R$.
• Power scaling and filtering: Non-collinear products from the double-pass multiplexing are spatially separated after the final lens and can be blocked with physical apertures or relayed to auxiliary applications.

Application Implications and Future Prospects

This three-dimensional AOD platform fills a substantial technical gap for fast, independent 3D control of laser foci in both academic and industrial domains. Specific implications include:

• Quantum device loading and rearrangement: Large, defect-free 3D neutral-atom arrays—a central element of neutral-atom quantum computing—require rapid filling and rearrangement of single atoms across layers. Conventional axial modulation is too slow for scalable architectures. The demonstrated 3D AOD enables layer-by-layer transport and rearrangement at rates exceeding atomic trapping lifetimes and dynamical timescales in state-of-the-art neutral atom devices [see, e.g., (Zhang et al., 27 Jun 2024)].
• Multi-plane and extended-depth microscopy: Volumetric neural imaging, high-speed two-photon microscopy, and multifocal light-sheet methods can leverage arbitrary 3D patterning for simultaneous parallel excitation, restricted by existing SLM update rates. The present architecture enables full 3D pattern updates at rates orders of magnitude faster than leading SLM platforms.
• Ultrafast laser processing: Three-dimensional, rapidly reconfigurable focal patterns allow advanced laser micromachining and multi-plane ablation, improving throughput and enabling complex patterning not possible with stage-based or slower electromechanical focus translation.
• Neutral atom transport and quantum networking: The axial focusing capability enables high-speed, non-mechanical translation of atomic ensembles over centimeter distances for modular quantum processing and network linking, where mechanical tunable lenses or slower elements have imposed key orchestration bottlenecks.
• AI-enhanced control and complex patterning: The hardware readily supports software-driven generation of arbitrary multi-spot, multi-plane patterns, making it amenable to integration with AI-based optimization and control schemes in high-throughput quantum device scheduling or intelligent microscopy.

Comparison with Related Technologies

The design outperforms SLM-based methods for reconfigurable multiplexing in 3D, which are limited to 1–10 kHz update rates and typically suffer from higher insertion loss and lower beam quality in certain regimes [see, e.g., Lin et al., Phys. Rev. Lett. 135, 060602 (2025)]. Pure acousto-optic lensing schemes based on chirped drivers are operationally complex and fundamentally limit 3D multiplexing, whereas the double-pass Littrow architecture enables simultaneous high-speed, multi-tone, and 3D addressing using only standard AOD devices without need for precise, time-varying chirped drive synthesis.

Conclusions

The paper presents a robust, accessible solution for fast 3D acousto-optic beam control by integrating a double-pass AOD/frequency-tunable lens in the Littrow configuration and crossed lateral AODs, achieving $\ge$22 $z_R$ axial range, $5 \times 5 \times 3$ multi-spot arrays, and $\ge$100 kHz switching rates with multiplexed operation. The system is suited for immediate application in quantum atom array platforms, advanced microscopy, and rapid laser processing and represents a significant advance in all-optical, non-mechanical beam steering and focusing.

Further optimization toward higher switching rates and dynamic range is possible via device miniaturization and fast-velocity AODs. The architecture is inherently compatible with AI-enabled dynamic pattern scheduling and will help underpin the next generation of scalable, high-speed, reconfigurable optical control systems for quantum and classical applications.