Development of a laser transceiver system for deep-space optical communications

The National Aeronautics and Space Administration (NASA) continues to plan and anticipate the development of high data rate communications for future deep space missions. The Johns Hopkins University Applied Physics Laboratory is responding to this challenge by developing a breadboard laser transceiver package using commercial off-the-shelf components. We plan to demonstrate a breadboard transceiver unit, integrated with a fine pointing and tracking capability by the end of FY-03. A potential mission application is to ultimately demonstrate a live video link from Mars. Our near-term demonstration goals are to achieve a modest 5 Mbps data rate over an equivalent range of 2 AU. To achieve this we are modeling and testing the components for a hybrid analog/digital receiver in conjunctino with semiconductor laser diodes and silicon PIN and avalanche photodiodes. Our efforts leading up to hardware implementation and test have consisted of a trade-of between coherent and direct detection receiver architectures, and a link analysis for deep space applications, which established the laser power requirements for supporting a real-time video link from Mars as well as other missions, where the encoded bit error rate is from 10-6 to 10-9. Current efforts include the development of a direct-detection 4-ary pulse position modulation scheme using a FPGA-based modulator/demodulator as well as a separate quadrant photodiode receiver for tracking. We plan to integrate this transceiver with lightweight diffractive optical elements for beam-forming. The design and initial testing of the transceiver components will be discussed.