Optical Technologies for On-board Processing of Microwave Signals

In the last decade, optics has proved a key technology for the transmission and handling of broadband signals in telecommunication networks. Future telecom satellite payloads will have to receive, process, route and re-transmit an increasing number of microwave signals. We have been investigating how the technologies inherited from terrestrial optical communications may bring substantial improvements or provide any breakthrough in satellite sub-systems. Optical technologies may contribute to the advent of new payload designs by enhancing or complementing conventional electronic functions, or by implementing new functions for which there is no satisfactory electronic solution. Critical issues such as EMC/EMI, RF isolation, mass, volume figures could be improved significantly as well. The investigated functions include optical distribution of high-frequency local oscillators (LO), optical frequency-conversion and optical cross-connection of microwave signals. Optical techniques can be used for distributing LO’s directly in the microwave or millimetre-wave range in many sub-systems of future payloads. They comply with low-phase noise requirements, while bringing drastic mass savings and suppressing isolation and EMC/EMI issues. However, it is necessary to produce a microwave LO under optical form, with low phase noise and power high enough to deliver to numerous equipment. This can be achieved for instance through double sideband modulation with carrier suppression of a high-power CW laser, by means of an electrooptical intensity modulator. Optical heterodyning of the first two side-bands at the photo-receiver generates the high-purity microwave signal frequency. Frequency mixing can be achieved as well by using an electro-optic intensity modulator that both is fed by a photonic local oscillator and is driven by a given microwave signal. The optical signal at the modulator output thus features frequency compounds at intermediate frequencies, so that frequency down-conversion is performed. Unwanted frequency compounds are filtered out after optical detection. A key attribute of such a mixer is its very broadband operation. It could even perform simultaneously multiple frequency down-conversion based on wavelength-divisionmultiplexing. An innovative repeater concept is briefly introduced as an example of how these optical building blocks may be combined advantageously and integrated in satellite payloads. It makes use of MEMS optical switches and was elaborated to perform broadband and flexible cross-connection in multiple-beam telecom missions. However, the scope of potential applications is certainly not limited to telecom sub-systems and these optical building blocks may also take place in remote sensing satellites. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 13 JUL 2005 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Optical Technologies For On-Board Processing Of Microwave Signals 5a. CONTRACT NUMBER