FIBER-OPTIC TRANSCEIVERS FOR HIGH-SPEED INTRA-SATELLITE LINKS

Mikko Karppinen, Antti Tanskanen, Jyrki Ollila and Veli Heikkinen VTT Technical Research Centre of Finland

Oulu, Finland

Introduction Current trends in satellites payload show a rapid increase in data traffic and digital processing. For instance, the throughput of next generation digital telecom satellites will exceed terabits per second of data, which have to be processed on board. On the other hand, the novel payload instruments, such as, high-resolution cameras and synthetic aperture radars call for high-speed communications between the instruments and storage. The design of such payloads is a significant challenge; given the performance provided by current electrical interconnect technology. However, the optical technology can potentially overcome these interconnection bottlenecks. Optical links have several advantages including the high data rates, almost distance-independent performance, high connector density and lightweight cabling. The cabling is also immune to electromagnetic interference. Consequently, optical links are studied for more extensive use in space, for instance, the European Space Agency (ESA) is developing the “SpaceFibre” high-speed point-to-point data links to extend the capabilities of the “SpaceWire” standard for spacecraft onboard communications. And for digital telecom payloads, optical interconnects are developed in order to enable very-high-throughput links between the processor ICs and boards and to improve the mass and power figures while also improving the thermal management. To best exploit the potential advantages of the optical interconnects, the generic target is to bring the optical interface close to the interconnected processor ICs. Transceiver Components VTT has developed high-performance fiber-optic transceivers for intra-satellite applications. The components integrate 850-nm vertical-cavity surface-emitting laser diodes (VCSEL) and photodiodes with multimode fibers, enabling data transmission up to 10 Gbps per fiber over short distances (<100 m). With VCSEL-based technology, the requirements of low-power dissipation can be met, also allowing high integration density. On the other hand, the ceramic packaging technology enables lightweight components and robustness for harsh environments. First generation transceivers have already passed environmental tests and further tests are ongoing. Packaging The transceivers are implemented using metal-ceramic packaging technology [1][2]. The transceiver electronics is realized on multilayer-ceramic substrates with surface mount electrical interfaces. The ceramic-based transmitter and receiver subassembly (T/ROSA) substrates also include the fiber alignment structures enabling the passive alignment of optical fibers to laser diode or photodiode. Hermetic sealing is made with a Kovar lid and frame soldered to the ceramic substrate. The hermetic fiber feed-through is made using a low temperature glass preform. The packages have passed leak tests after been stressed with 500 temperature cycles between -55 and +125 °C. Intra-Satellite Data Links An example of the components is “SpaceFibre” 6.25 Gbps transceiver, which is developed to match with ESA’s planned “SpaceFibre” standard [3]. The full-duplex transceiver integrates 850-nm VCSEL and GaAs PIN photodiode with their driver and amplifier electronics and with 50/125-µm graded-index fiber pigtails. The transceiver has typical power consumption of 230 mW, and its weight is 4 grams without fiber pigtails and connectors. Operating temperature range is from -40 to +85 °C. The first generation prototypes already passed environmental tests showing that the “SpaceFibre” link is a promising candidate for the upcoming high-speed intra-satellite networks [1], and the testing of second generation prototypes is ongoing.

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Parallel Optic Transceiver Another component is a parallel optic transceiver developed for very high-bit-rate interconnects, to be used for instance in board-to-board links in high-throughput onboard processors. It is a quad transceiver component operating up to 10 Gbps/channel full-duplex, i.e. it has 4 transmit and 4 receive fibers. The metal-ceramic package integrates 4-channel 850-nm VCSEL and 4-channel photodiode arrays with their driver and amplifier electronics, and it is equipped with 8-fibre ribbon pigtail of 50/125-µm fibers and with multi-fiber connector. Its weight is 5 grams (without fibre pigtails and connectors), power consumption is ca 700 mW, i.e. ca 18 mW/Gbps for full link, and it is for operating temperature range from -40 to +85 °C.

Figure 1. left) VTT’s “SpaceFibre” transceivers with Radiall LuxCis connectors; right) VTT’s 4+4-channel

transceiver with MTP fiber-ribbon connector Conclusion High-bit-rate fiber-optic transmitter and receiver components were developed for intra-satellite data links, which will benefit from reduced EMI and savings in mass and volume. The ceramic-based fiber-optic packages enable robustness for harsh environments. Two kinds of components were introduced: “SpaceFibre” transceivers (>6 Gbps) and parallel optic transceivers with fiber ribbon cables (4+4 x 10 Gbps), both based on 850-nm VCSEL sources and multimode fibers. The transceivers are expected suitable also for other harsh environment applications. References [1] V. Heikkinen, T. Alajoki, E. Juntunen, M. Karppinen, K. Kautio, J. –T. Mäkinen, J. Ollila, A. Tanskanen, J. Toivonen, R. Casey, S. Scott, W. Pintzka, S. Thériault, and I. McKenzie, “Fiber-optic transceiver module for high-speed intrasatellite networks,” Journal of Lightwave Technology, vol. 25, no. 5, pp. 1213–1223, 2007. [2] V. Heikkinen, E. Juntunen, M. Karppinen, K. Kautio, J. Ollila, A. Sitomaniemi, A. Tanskanen, R. Casey, S. Scott, H. Gachon, M. Sotom, N. Venet, J. Toivonen, T. Tuominen, and N. Karafolas, “High-speed ADC and DAC modules with fibre optic interconnections for telecom satellites”, International Conference on Space Optics (ICSO), 2008. [3] T. Tuominen, V. Heikkinen, E.Juntunen, M. Karppinen, K. Kautio, J. Ollila, A. Sitomaniemi, A. Tanskanen, M. Pez, N. Venet, I. McKenzie, R. Casey and D. Lopez, “SpaceFibre – high speed fibre optic data links”, Proc. of 3rd Internat. SpaceWire Conference, pp. 159–162, 2010.

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