Date of Award
Spring 6-4-2025
Document Type
Thesis (Undergraduate)
Department
Computer Science
First Advisor
Adithya Pediredla
Abstract
Acousto-optic light steering based on the Raman-Nath
diffraction regime has previously been demonstrated using
water as the acousto-optic medium, enabling underwater
backscatter communication at speeds up to 0.66 Mbps—a
substantial improvement over traditional systems limited to a
few kilobits per second. In these systems, a remote underwa-
ter asset is illuminated by a pulsed laser from a base station
and uses a retroreflector to return the beam. An embed-
ded acousto-optic system dynamically steers the returning
beam toward or away from a photodetector to encode binary
data. In this thesis, we extend acousto-optic beam steer-
ing to solid media by adapting a commercial acousto-optic
modulator (AOM), which typically operates in the Bragg
diffraction regime, to instead function in the Raman-Nath
regime. By carefully focusing the incident beam within the
AOM’s Lead Molybdate (PbMoO4) crystal, we reduce the in-
teraction length and enable dynamic, high-speed light steer-
ing. Our implementation uses a 40 MHz transducer, with
each bit repeated three times, enabling a backscatter com-
munication rate of 13.33 Mbps—a 20× speedup over prior
water-based systems. In this setup, our max communication
speed is constrained by the max laser pulse speed (13.33
MHz). To demonstrate that higher speeds can be achieved
with higher frequency AOM without illumination limitations,
we also develop a continuous-wave (CW) laser setup with
a novel demodulation scheme. Using this configuration, we
demonstrate reliable communication at 8 Mbps (with 5×
bit repetition), limited primarily by the AOM transducer
speed and receiver design, rather than by the laser source
itself (opening the door for further order-of-magnitude in-
creases in speed). These results show that solid-medium
AOMs can serve as compact, robust, and scalable platforms
for high-speed underwater optical communication, offer-
ing an order-of-magnitude increase in bitrates over prior
approaches.
Recommended Citation
Agashe, Atharv Vinay, "Solid Medium Acousto-Optic Beam Steering for Underwater Optical Backscatter Communication" (2025). Computer Science Senior Theses. 89.
https://digitalcommons.dartmouth.edu/cs_senior_theses/89
