Norbert Venet

Applications of Optical Techniques in Future Communication Payloads

Optics and photonics bring unusual but attractive and performing solutions for implementing functions in communication payload. For the time being, these techniques have been mostly put aside for various reasons, but the technical world changing very fast, it is advisable to check if they could be competitive alternatives. Moreover, new functions will appear in the next generation of broadband satellites in response to the increasing needs for bandwidth, connectivity and flexibility. Optical techniques should be both viable solutions to enhance existing functions and the only solutions to create the new functions of broadband satellites to come. Alcatel Space research department has identified functions and equipment where optical techniques could be either a significant and necessary breakthrough or simply a technical and cost improvement. For mid term, Alcatel Space has selected and studied three functions where optics is particularly attractive for performances, mass saving and cost. First application is backplane interconnections. This technology allows gigabit connections required inside onboard large digital processors. A second application is the transport and distribution of microwaves onto optical fibers. Fibers are an interesting substitution for coaxial harness in payloads. Associated with the emerging Optical Micro-Electro-Mechanical Systems (OMEMS), this technique will extend the routing capability of payloads. A third application is intrasatellite data link. Optic fibers or wireless infrared links are promising choices to build onboard data handling system. In the long term, optical techniques could change the very aspect of repeaters and antennas of communication payloads. However, the introduction of optics for space applications is neither easy nor rapid. This paper summarizes Alcatel Space research effort and the main results in this domain. I. Optics in broadband payloads In the next five to ten years, satellite operators are anticipating the creation of a new market for satellite: broadband communications. Typically, broadband systems should offer high data rate connections to very large numbers of low price terminals. The present generation of satellite is not really suited for broadband missions involving millions of end users. Ku and C bands are too congested to offer sufficient room for growth. Receive performances of the satellite are not sized for the use of small and power limited terminals. Multiple access schemes are not adapted, as there are, for managing tens of thousand simultaneous links. A new family of satellite shall be designed to cope with these unusual requirements. Lastly, to be economically viable, communication price shall be as low as possible. Only satellites with very large capacity in term of bandwidth or number of circuits would achieve low communication price. Several techniques are investigated to increase significantly the satellite capacity [1]. Broadband payloads will have complex multi-beam antennae, hundreds of channels to receive, to route and to transmit, large onboard processors for regenerating and switching digital signals... Optics and photonics bring unusual but attractive and performing solutions for implementing these functions. Optical techniques should be viable solutions to enhance existing functions in mid term. In the long term, optical techniques will be the only solution to create the new functions of the broadband satellites to come. II. Mid term utilization of optical techniques In mid term, optical techniques could complete or replace existing functions in communication payloads: digital intra-satellite links (Onboard Data Handling System), microwaves on optical fibers, gigabit backplane interconnections in high throughput On-Board Processor (OBP), high speed data packet switching, inter-satellite and inter-orbit links, pyrotechnic harness, signal interfaces of cryogenic electronic units... 21st International Communications Satellite Systems Conference and Exhibit AIAA 2003-2297 Copyright

Multi-gigabit optical interconnects for next-generation on-board digital equipment

Parallel optical interconnects are experimentally assessed as a technology that may offer the high-throughput data communication capabilities required to the next-generation on-board digital processing units. An optical backplane interconnect was breadboarded, on the basis of a digital transparent processor that provides flexible connectivity and variable bandwidth in telecom missions with multi-beam antenna coverage. The unit selected for the demonstration required that more than tens of Gbit/s be supported by the backplane. The demonstration made use of commercial parallel optical link modules at 850 nm wavelength, with 12 channels running at up to 2.5 Gbit/s. A flexible optical fibre circuit was developed so as to route board-to-board connections. It was plugged to the optical transmitter and receiver modules through 12-fibre MPO connectors. BER below 10-14 and optical link budgets in excess of 12 dB were measured, which would enable to integrate broadcasting. Integration of the optical backplane interconnect was successfully demonstrated by validating the overall digital processor functionality.