High speed optical interconnection using embedded PDs on electrical boards

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As the data rate of electronic circuitry dramatically increases, interconnection speed becomes one of the critical bottlenecks in the overall performance of current data processing systems. A number of alternative approaches have been suggested to improve the current interconnection performance in terms of operational speed, power consumption, and area [I, 2, 3, 41. As an alternative for current electrical interconnections, optical interconnections offer several attractive features. Advantages of optical interconnections include low power consumption, a significant reduction in interconnect footprint, and robust signal quality in high density interconnection systems because of immunity to electromagnetic interference. There are a number of approaches toward the integration of optical signals into an electrical interconnection system. One approach utilizes waveguides and beam turning devices (e.g. mirrors, gratings) to address surface normal photodetectors (PDs) and vdcal cavity surface emitting lasers (VCSELs) which can he hump bonded onto the modnle. A second approach also utilizes waveguides, however, the PDs and/or edge emitting lasers (EELS) are embedded in the waveguidehbstrate sample, as shown in Figure I, and evanescent field or direct coupling from the waveguide to the PD can he used to address the PD. This approach achieves alignment through assembly and successive masking layers and does not need optical beam turning devices. Thus, this optical interconnection integration mimics the transition in electronics fiom discrete packaged components to integrated circuits in the 1970s, through the integration of these embedded optical interconnections and active components. A great deal of research to date has focused upon the implementation of polymer optical waveguides with standard electrical interconnection substrates, and there have been demonstrations of polymer waveguides addressing PDs fabricated in Si and GaAs substrates. This paper describes the heterogeneous integration of independently optimized polymer waveguides, embedded thin film InGaAs PDs operating at a wavelength of 1300 nm, and a standard Si substrate; thus using a different material for each of the three components in the embedded optical waveguide interconnection. Finally, an integrated circuit is attached to the electrical interconnection substrate and wire bonded to the embedded PD, as shown in Figure 1. This work represents steps toward chip to chip embedded optical interconnections