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IEEE Transactions on Applied Superconductivity

Optical input/output interface system for Josephson junction integrated circuits

K. Nakahara, Hideyuki Nagaishi, Hiroaki HASEGAWA, S. Kominami, Hirotaka Yamada, T. Nishino

Published Jan 1, 1994• 10 citations
Publisher

Abstract

An optical input/output interface system for a Josephson junction integrated circuit is fabricated and tested. The system consists of a superconducting optical detector, a dc powered Josephson circuit, a dc powered Josephson high voltage circuit, a liquid-He-cooled semiconductor amplifier, and a liquid-He-cooled semiconductor laser. Features of the system are use of an ultrathin NbN film for the optical detector and adoption of the dc powered Josephson circuits for logic operation circuits. Correct optical output signal is detected by a liquid-He-cooled semiconductor photodiode. The optical input/output interface has the advantage of low heat penetration and low crosstalk compared to the interface using conventional coaxial lines. Moreover, dc powered Josephson circuits have an advantage of low crosstalk from power supply lines compared to conventional Josephson circuits, which are driven by ac supply current.>

DOI
10.1109/77.334963

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IEEE Transactions on Applied Superconductivity•Jun 1, 1995•5 citations
An optical input/output interface system for a Josephson junction integrated circuit is fabricated and tested. The system consists of a superconducting optical detector, a dc powered Josephson circuit, a dc powered Josephson high voltage circuit, a liquid-He-cooled semiconductor amplifier, and a liquid-He-cooled semiconductor laser. Features of the system are use of an ultrathin NbN film for the optical detector and adoption of the dc powered Josephson circuits for logic operation circuits. Correct optical output signal is detected by a liquid-He-cooled semiconductor photodiode. The optical input/output interface has the advantage of low heat penetration and low crosstalk compared to the interface using conventional coaxial lines. Moreover, dc powered Josephson circuits have an advantage of low crosstalk from power supply lines compared to conventional Josephson circuits, which are driven by ac supply current.>
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.>
We have fabricated Josephson vortex flow transistors (JVFTs) that consist of a parallel array of Josephson junctions and a control current line to apply the external magnetic field at the junctions. We observed modulations of the flow voltage with a DC current input. From these results, we estimated the mutual inductance and the self-inductance, and calculated the operation frequency of the JVFT. Next, femtosecond laser pulses modulated by an optical chopper were irradiated to the Josephson junction array. As a result, we observed an increase in the output voltage in the current-voltage characteristics, and the clear modulation of the output voltage with the same period as the optical chopping rate. These results suggest that a JFVT can operate as an optical input interface for superconducting circuits.
Josephson-junction-based low temperature rapid single flux quantum (RSFQ) superconducting electronics is already a mature technology, which is expected to perform at speeds exceeding 100 GHz [1]. However, the RSFQ technology still lacks a fast enough output interface between its operating circuit temperature T = 4.2 K and the room temperature electronic environment. RSFQ circuits work at liquid helium temperatures and the direct interconnection of these circuits and room temperature circuits using, e.g., copper transmission lines would consume too much of the cooling power [2]. To solve this problem a magneto-optical (MO) output interface has been proposed [3], in which the output current pulse from the RSFQ circuit is converted into an optical pulse and delivered to room temperature readout circuitry via an optical fiber.
A number of current approaches to quantum and neuromorphic computing use superconductors as the basis of their platform or as a measurement component, and will need to operate at cryogenic temperatures. Semiconductor systems are typically proposed as a top-level control in these architectures, with low-temperature passive components and intermediary superconducting electronics acting as the direct interface to the lowest-temperature stages. The architectures, therefore, require a low-power superconductor-semiconductor interface, which is not currently available. Here we report a superconducting switch that is capable of translating low-voltage superconducting inputs directly into semiconductor-compatible (above 1,000 mV) outputs at kelvin-scale temperatures (1 K or 4 K). To illustrate the capabilities in interfacing superconductors and semiconductors, we use it to drive a light-emitting diode (LED) in a photonic integrated circuit, generating photons at 1 K from a low-voltage input and detecting them with an on-chip superconducting single-photon detector. We also characterize our device's timing response (less than 300 ps turn-on, 15 ns turn-off), output impedance (greater than 1 MΩ), and energy requirements (0.18 fJ/um^2, 3.24 mV/nW).
For broadband data communication between Josephson and CMOS digital systems, amplification of small Josephson-output signals and synchronization between the systems are important issues. We present an interface circuit for a Josephson-CMOS hybrid digital system. The interface circuit consists of a parallel-in-parallel-out (PIPO) circuit and built-in Josephson-MOS amplifiers. The PIPO circuit, implemented based on 4JL latching logic technology, performs synchronized data transfer between the Josephson and CMOS circuits. The Josephson-MOS amplifiers consists of stacked Josephson junctions (Suzuki stacks) and MOS inverters which are monolithically integrated on a chip. The circuits have been designed, fabricated and tested. We have successfully confirmed correct operation of the circuits.
An ultrafast optical interface between superconducting and room-temperature electronics is proposed to take full advantage of high-speed superconducting circuits. We report on the computed and experimental studies of an optical receiving and modulating system that is compatible in processing with the prevailing integrated-superconducting-circuit technology. Planar interdigitated Nb/Si/Nb metal-semiconductor-metal (MSM) photodiodes are demonstrated as optical receivers with resolvable bit-rate as high as 38 Gb/s, and the response of MSM diode was shaped to be a single-flux-quantum pulse to drive Josephson-junction-based circuits. A similar interdigitated structure on a silicon waveguide is proposed to be an ultrafast light-intensity modulator, with its operation based on carrier-density modulation of the optical index of refraction. This field-effect device has insignificant power dissipation, in addition to high speed. A sample modulator with 5-V bias is shown to have a modulation depth of 40% and a bandwidth over 70 GHz.>