<title>Optical interconnects for high-speed data links</title>

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ABSTRACT We demonstrate the integration of vertical-cavity surface-emitting laser (VCSEL) arrays with Si-dummy chips for potentialuse in short-distance parallel optical interconnects. An 8x8 flip-chip bonded InGaAs (980 nm) VCSEL array was successfullymodulated at data rates up to 0.8 Gbit/s/channel, corresponding to an aggregate data transmission capacity in excess of 50Gbit/s. A 2x4 GaAs (850 nm) VCSEL array was indirectly flip-chip bonded to a Si substrate via a transparent glass carrierand package-limited data rates of 0.4 Gbitls/channel were achieved. The large signal modulation bandwidth ofthese devicesexceeded 2 Gbit/s. The electrical driving characteristics of the devices were found to be compatible with 3.3 V CMOStechnology. Keywords: VCSEL array, Optical interconnect, Flip-chip bonding, Hybrid integration 1.INTRODUCTION There has been much interest in the development of interconnects for high speed data communications at the board and chiplevels. Conventionally, this has been achieved using electrical interconnects. However, electrical interconnects suffer from anumber of drawbacks, including pin crowding, complex and costly fabrication of the printed circuit boards, with the strictrequirement of impedance matching, and the bandwidth limitations of the back-plane [1]. The development of very largescale integrated circuit (VLSI) technology has allowed higher integration density and faster clock speeds to be achieved,enabling higher data communication rates. Electrical interconnects are unlikely to meet the ever increasing high-bandwidthhigh density requirements. Therefore, there is strong interest in using optical interconnects to overcome the bottleneckexperienced by conventional interconnects. Optical interconnection offers not only a high interconnect density and largebandwidth, but also EMI immunity, low power consumption and potential low cost, making it advantageous to implementthis technology in a wide range of systems. Free-space optical interconnects have been recognized as a suitable method toimprove interconnect performance [3]. The development of such interconnects relies on the development of inexpensive