Undersea Laser Communications Field Test at the Naval Undersea Warfare Center (NUWC)
MASSACHUSETTS INST OF TECH, LINCOLN LAB LEXINGTON United States
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Narrow-beam laser communication lasercom has the potential to maximize both the achievablerange and data rate of undersea optical communications. MIT Lincoln Laboratory conducted a fielddemonstration of narrow-beam undersea lasercom from 28 March-1 April 2016 at the Naval UnderseaWarfare Center NUWC in Middletown, RI. Transmit and receive hardware were placed in twowatertight containers and attached to the ends of an aluminum truss, which was lowered alongside a pierinto the Narragansett Bay. A green 515 nm wavelength collimated laser beam was modulated andsteered into a receiver with four sensors two cameras to provide alignment and beam characterizationdata and two photodetectors to provide distinct high-speed communications demonstrations. The firstdemonstration utilized a single-photon sensitive photomultiplier tube PMT and achieved data rates up to8.7 megabits per second Mbps over a distance of 7.6 meters, which corresponded to between 8-12 beamextinction lengths. The PMT demonstration included real-time electronics to perform synchronization andforward error correction and achieved a sensitivity of better than 1.5 detected photons per bit. In thesecond demonstration, a 125 Mbps communications link was demonstrated over 4.8 meters 5 beamextinction lengths with an APD receiver. Communications and characterization data were collectedthrough a variety of conditions over the five-day field experiment, including day and night, calm and highwinds, and flood and ebb tide robust communication performance was achieved throughout. In theexperiment the transmit power, receiver field of view, and link distance were varied. The watertransmissivity and volume scattering function were measured throughout the experiment to calibrate theresults. The field test data for both communication and beam propagation characterization provide in-watervalidation of model-generated lasercom performance predictions.