Using an Acousto-Optic Modulator as a Fast Spatial

Light Modulator
Xialin Liu1,2, Boris Braverman1,*, Guihua Zeng2 and Robert W. Boyd1,3
1
Department of Physics, University of Ottawa, Ottawa, ON, Canada K1N 6N5 14627
2
School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
3
Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA 14627
* bbraverm@uottawa.ca
Abstract—We generate arbitrary 1-dimensional spatial the two beams. Fig. 2 illustrates the generation of a beam
profiles in a laser pulse by mapping the temporal electrical approximating an HG3,0 mode, with the overlap between the
waveform sent to an acousto-optic modulator (AOM). The AOM predicted and realized mode equals to 92%. The effective pixel
can be therefore used as a spatial light modulator with 45 µm pixel size we realize with our AOM-SLM is approximately 45 µm,
pitch, fast refresh rate, and high damage threshold.
currently limited by the response time of the piezo driving the
Keywords—Spatial modes generation, Acousto-optic modulator crystal. Across the 2 mm signal beam width, we can have 52
pixels with independently controllable amplitude and phase.
The generated spatial mode can be arbitrarily reprogrammed,
I. INTRODUCTION
with a rate limited by the transit time of sound waves across the
Generation and manipulation of spatial modes of light is most beam waist, equal to 600 ns for a 2 mm beam waist.
often realized using spatial light modulators (SLMs). While Our results suggest that for applications to high-power or
SLMs are versatile and have a multitude of applications [1], short wavelength pulsed lasers that could damage an SLM,
they suffer from two major drawbacks. First, they are slow: a using an AOM is an attractive approach. An improved
long time on the order of ms is needed to update the generated experimental configuration could be made by passing the beam
spatial mode. Second, SLMs have a low damage threshold and through the AOM a second time. In that case, high efficiency
high losses due to the use of liquid crystal molecules. AOMs would be attained by phase-only modulation. Moreover, our
offer both high speed and high damage threshold, and have fast modulator is expected to greatly improve the speed of
been used to implement simple optical elements, such as single-pixel imaging [4], which is currently limited by the
cylindrical lenses, by imprinting a chirped acoustical signal in refresh rate of SLMs.
the crystal [2,3]. Here, we show that an AOM can be used as an
SLM. The spatial grating formed by the sound waves in the
AOM nearly reproduces the incident RF waveform, and is
imprinted on the spatial mode of the diffracted light.
II. EXPERIMENTAL DESIGN
A schematic of the experimental apparatus is shown in Fig. 1.
Light pulses are generated and are coupled into a single-mode
fiber to produce a consistent spatial mode. The light is then
coupled back into free space and split into two beam paths:
signal and reference. Signal light passes through the AOM, Figure 2. (a) Image of interference pattern. (b) Reconstructed complex field
where a portion is diffracted, replicating the spatial pattern distribution, with brightness corresponding to beam amplitude, and hue
corresponding to the phase. (c) Comparison between the RF waveform and
produced by the RF waveform from an arbitrary waveform generated spatial mode. Note that the imaginary component plots are shifted
generator (AWG). We reconstruct the complex electric field of upward by 0.15 units for clarity.
the signal beam using off-axis holography.
IV. REFERENCES
[1] A. Forbes, A. Dudley, and M. McLaren, Adv. Opt. Photon. 8, 200–
227 (2016).
[2] A. Kaplan, N. Friedman, and N. Davidson, Opt. Lett. 26, 1078–1080
(2001).
[3] G. Konstantinou, P. A. Kirkby, G. J. Evans, K. M. N. S. Nadella, V.
A. Griffiths, J. E. Mitchell, and R. A. Silver, Opt. Express 24, 6283–
6299 (2016).
Figure 1. Experimental setup for employing an AOM as a SLM. [4] X. Liu, J. Shi, X. Wu, and G. Zeng, Sci. Reports 8, 5012 (2018).
III. EXPERIMENTAL RESULTS AND DISCUSSION
We recover both the amplitude and phase information of the
spatial mode generated by analyzing the interference between

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