Spaceborne fiber coupled diode laser pump modules for intersatellite communications

Compared to traditional microwave systems for intersatellite communication, optical intersatellite links offer numerous advantages for example lower weight and power consumption as well as higher bit rates. In addition, the smaller diameter of the laser beam allows a higher data security. The coherent optical terminal developed by TESAT Spacecom offers a bandwidth of 5.5 Gbps with a range of 10,000 km and a bit error ratio below le-9. In 2007, the coherent optical terminal will be verified in orbit. The transmitter consists of a ring oscillator and an optical amplifier. For both components, a high reliable diode laser pump module is essential to meet the demanded lifetime requirements of 10 years with a reliability of 0.9998. Built-in cold and hot redundancy as well as a truly hermetically sealed housing increase the reliability of the pump module. To prove its suitability for space applications, the module has been successfully qualified in terms of radiation, vibration, mechanical shock and thermal cycling. The laser radiation of two diode laser bars consisting of six emitters is coupled in a 100 um NA=0.22 fiber. The coupling efficiency as well as the mounting accuracy of the optical components have been analyzed by raytracing. To predict the effect of different heat sink materials and to calculate the temperature drop over the module, a 3D finite element analysis has been performed. The rated optical output power of the module described in this paper amounts to 10 W, and it measures 50 mm × 50 mm × 20 mm.