A three-dimensional acousto-optic deflector

TL;DR

This work addresses the lack of rapid, fully three-dimensional light control by introducing a three-dimensional acousto-optic deflector (AOD) that multiplexes both axial and lateral beam directions. The authors realize a compact, frequency-tunable lens by marrying a double-pass AOD with a Littrow-configured grating, enabling fast 3D focus tuning and arbitrary multi-focal patterns. They demonstrate long-range axial tuning (over ~22 $z_R$) with switching up to 100 kHz and show flexible 3D pattern generation by integrating lateral AODs, producing 3D arrays of spots and needle beams. The platform offers a broadly applicable route to rapid 3D beam control with potential impact on high-resolution microscopy, laser processing, and scalable neutral-atom quantum technologies.

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.

Figures (5)

• Figure 1: Illustrations of three-dimensional beam scanning system. (a) Optical setup of axial focus scanning module using a double-pass acousto-optic deflector (AOD) with a cat's eye lens (CEL) and a grating in the Littrow configuration. The grating has an angle $\theta$ relative to the incident beam, such that the first order diffracted beam is retroreflected along the incoming path. We indicate the optical path length difference $\Delta z$ between two beam deflection positions separated by an angle $\phi$, which results in a different defocus for each deflection angle. Because the AOD requires horizontal input polarization, and rotates the polarization of the diffracted light by 90$^\circ$, we use a Faraday rotator and a half-waveplate to separate the incoming and outgoing beams at a polarizing beam splitter. The beam is then re-focused to a spot with another achromatic lens with a focal length $F$. (b) Optical setup allowing for arbitrary scanning of a focal spot and multiplexed array generation in three dimensions using three AODs. The axial scanning module is imaged onto a pair of crossed AODs for x and y tuning using a 3:2 telescope in the 4-f configuration. (c) Illustration of a 3D array of optical tweezers created with our system, by sending superimposed beams with different defocus and input angles through a focusing lens.
• Figure 2: Characterization of long-range focus tuning module. (a) y-z cut of the test beam profile for five different focus positions spanning the full bandwidth of the AOD used for focus tuning. All profiles are normalized to the maximum intensity at the center of the bandwidth. (b) Gaussian beam waist fits at various z-positions for five different frequencies spanning the full bandwidth of the AOD used for focus tuning. The z dependence of the waist is fit using a Gaussian profile with the Rayleigh range $z_R$, focus size $w_0$, and focus position as free parameters. (c) Dependence of focus position along z on AOD frequency, showing the linearity of focus tuning with AOD deflection angle, as predicted by Eq. 1. (d) Displacement along z, perpendicular to the AOD axis, of the beams generated by each RF tone, as a function of distance from the focus of that beam. The shaded area is a guide to the eye showing the beam waist as a function of z, using the fit paraemeters from the central (100 MHz) spot. (e) Displacement along z, parallel to the AOD axis, as a function of distance from the focus.
• Figure 3: Characterization of axially multiplexed beam. (a) Maximum intensity at each z-position of camera as it is scanned along the axis of an axially multiplexed beam. Fit is performed to a sum of Gaussian beam profiles. (b) y-z cut of the intensity profile of the multiplexed beam.
• Figure 4: Profiles of 3D intensity patterns generated using three AODs. (a-c) Images showing x-y, x-z and y-z cuts of a 5-by-5-by-3 array of focused optical-tweezer-like spots generated using the setup. Dashed lines in each image indicate the planes along which the orthogonal cuts are displayed. (d-f) x-y, x-z and y-z cuts of a 5-by-5 array of needle beams.
• Figure 5: Characterization of switching rate of the acousto-optic lens. (a) Optical setup used for testing rapid focus switching. With a focusing lens of $F = 250$ mm, the separation between the focii $F_2-F_1$ is approximately 90 mm. The irises in each path are aligned so as to maximize transmission of one tone and minimize background transmission of the other. (b) Signals of each photodiode (PD) when switching between two focus positions at 10 kHz. (c) Switching between two focus positions at 100 kHz.