Sensors which collect information for intelligence, surveillance and reconnaissance generate a substantial amount of data. High data rates are required to transmit the information in reasonable time intervals. This paper describes the objectives and progress on the development of laser communication terminals for aircraft, transmitting high speed data over distances greater than 100 kilometers. The terminals are being designed and built under the Air Force Research Laboratory’s EO Sensor Technology & Evaluation Research (ESTER) program.
The free space laser communication system consists of three terminals developed around commercial fiber-optic standards. They are designed to be an open system, full duplex, protocol neutral, and operate at 2.5 gigabit per second, capable of expanding to 10 gigabit per second. The terminal’s data rate can be reduced if atmospheric effects cause a significant increase in bit error rate. The free space optics are mounted in a pointing & tracking gimbal which interfaces with an avionics unit that measures aircraft GPS information. Fine pointing and tracking is maintained by using a beacon signal which switches from wide to narrow divergence when signal lock is achieved. The terminals are designed to operate in air-to-ground and air-to-air scenarios. Subsystem laboratory tests are being completed and the terminals are being prototyped. The first set of tests will be conducted between ground sites and the first flight demonstration will involve interfacing with the multi-purpose common data link (MP-CDL) on an aircraft.
We provide a description of our terminal design, show our estimated operational performance, describe the results of laboratory testing, and outline the future program activities.