COHERENT COMMUNICATION LINK USING DIODE-PUMPED LASERS

OPTICAL COMMUNICATION LINKS BETWEEN GEOSYNCHRONOUS SATELLITES, OR BETWEEN DEEP SPACE PROBES AND 2 SPACE STATION ORBITTING THE EARTH, WOULD HAVE THE ADVANTAGE OF SMALLER ANTENNA SIZE AND/OR LOWER POWER CONSUMPTION THAN MICROWAVE LINKS WITH SIMILAR CAPACITY. BANDWIDTH AND SECURITY WOULD ALSO BE IMPROVED. DIODE-PUMPED SOLID STATE LASERS HAVE THE POWER, THE EFFICIENCY, AND THE BEAM QUALITY NEEDED FOR THESE LINKS. IN ADDITION, THE TECHNOLOGY OF SINGLE-FREQUENCY MONOLITHIC DIODE-PUMPED LASERS, COMMERCIALLY PIONEERED BY LIGHTWAVE, PROVIDES THE COHERENCE NEEDED TO UTILIZE COHERENT COMMUNICATION TECHNIQUES SUCH AS HETERODYNE DETECTION. HETERODYNE DETECTION PROVIDES BETTER DETECTOR SENSITIVITY, ESPECIALLY IN THE PRESENCE OF A BRIGHT BACKGROUND. LIGHTWAVE PROPOSES TO DEVELOP UNDER THIS CONTRACT A 1.32-MICRON SINGLE-FREQUENCY LASER WITH OUTPUT OF SEVERAL HUNDRED MWATT. THIS LASER WOULD BE COUPLED INTO A COMMERCIALLY-AVAILABLE GUIDED-WAVE PHASE MODULATOR WITH A BANDWIDTH OF 3 GHZ. THE MODULATED OUTPUT WOULD BE HETERODYNE-DETECTED USING ONE OF LIGHWAVE'S 5-MW SINGLE-FREQUENCY, QUICKLY-TUNABLE LASERS. THESE TUNABLE LASERS HAVE BEEN PHASE-LOCKED AT LIGHTWAVE. THE PROBLEM OF LONG-TERM FREQUENCY STABILIZATION, WHICH IS A CONSIDERATION DETERMINING SYSTEM ROBUSTNESS, WOULD BE STUDIED.