Optical data communication between Josephson-junction circuits and room-temperature electronics

The feasibility of optical data transmission to and from Josephson junction circuits, using metal-semiconductor-metal (MSM) photodiodes and GaAs/AlGaAs semiconductor laser diodes with sub-mA threshold current, is demonstrated. Standard devices can be used with the exception of a cooled GaAs detector. It is shown that silicon MSM detectors compatible with Josephson junction circuits can be fabricated. While these detectors show large photoconductive effects at room temperature they behave as good-quality photodiodes at low temperatures. Power dissipation in the laser diode scales with temperature while maintaining the modulation frequency. It is also shown that the combination of a laser diode and a photodiode provides the voltage gain needed to interface Josephson-junction circuits with room-temperature electronics. Experimental results on MSM detectors and laser diodes are presented. Expected power dissipation is below 1 mW per input/output (I/O) at a data rate of 1 Gb/s.<
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