Optical Technologies for On-Board Processing of Microwave Signals

摘要

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.