Latest results from the 32 km maritime lasercom link at the Naval Research Laboratory, Chesapeake Bay Lasercom Test Facility

Abstract

The Naval Center for Space Technology at the Naval Research Laboratory reports the latest results from the long-range, maritime, free-space lasercom test facility located between Chesapeake Beach, MD and Tilghman Island, MD. The two sections of the facility are separated by 16.2 km of the Chesapeake Bay. Using a new OC-48 receiver developed by NRL's Optical Science Division with a sensitivity of -33dBm for 10 -9 bit error rate at 2.5 Gbps, we have closed a 32.4 km maritime lasercom link (round trip across the Chesapeake Bay) and performed bit error rate testing while transmitting 1.13 Terabytes of data. Bit error rate testing was also performed at lower data rates when atmospheric conditions were not favorable for high speed (2.5 Gbps), including testing at 150 Mbps through light fog and rain. In addition, we have set up a system for digitizing and transmitting full-color, uncompressed, video along with six audio channels and three RS-232 data channels over the maritime link. The digital link operated at 311 Mbps and could be maintained indefinitely, depending on atmospheric conditions. Several complete videos were transmitted in entirety or in part as well as live video from a handheld camcorder to test the system operation and robustness. The transmitter and receiver were co-located on the western shore of the bay at the NRL Chesapeake Bay Detachment. The data for both the bit error rate testing and the video was transmitted across the bay and returned from an array of retroreflectors located on a tower at Tilghman Island on the eastern shore. The lasercom links were closed with static pointing and with no active atmospheric aberration mitigation such as adaptive optics or fast steering mirrors on the receiver optics.

Overview of NRL's maritime laser communication test facility

“…Many of the results have been previously reported [1][2][3] . Recently, with the construction of the multi-mode fiber O-E-O receiver, we have begun OC-48 testing in various conditions over our 32 km folded path test range.…”

“…Additionally, lack of RF radiation allows operation of lasercomm systems in conditions when RF communications are not advisable. A typical ship-to-ship lasercomm transceiver would be small (~2 ft 3 ), lightweight (~30 lbs), and consume relatively low power (~100 watts). These qualities of a lasercomm system make lasercomm highly desirable for Naval communications.…”

Large diameter high-speed InGaAs receivers for free-space lasercom

“…Previously, results have been reported on our round trip propagation results, where an array of 25 solid retroreflectors located on a tower on NRL-Tilghman Island, MD folded the optical link back to the CBD facility on the western side of the Chesapeake Bay [15][16][17][18][19][20] . The conversion to a one-way propagation path allows for a more accurate characterization of the path because the angle-of-arrival and C n 2 measurements are made along one direction.…”

“…These thermal gradients change on a time scale of several minutes to hours, depending on the weather conditions. [14][15][16][17] The output of the communication receiver (APD #3) is used for BER testing, packet error rate (PER) testing or video transmission. Details of the test setups and comparisons of BER and PER testing have been presented previously in reference 20.…”

Steering compensation for strong vertical refraction gradients in a long-distance free-space optical communication link over water

“…A fiber positioner directed by a position-sensing detector (PSD) is able to correct the elevation errors caused by the strong thermal gradients. The system was installed and tested at the Naval Research Laboratory Chesapeake Bay lasercom testbed 2,3,4 located at NRL's Chesapeake Bay Detachment (CBD). Figure 1 shows the compilation of approximately 3 months of turbulence data taken over the Bay at the Lasercom Testbed 5 .…”