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Applied Physics Letters

1550 nm band optical input module with superconducting single-flux-quantum circuit

Satoshi Shinada, Hirotaka Terai, Zhen Wang, Naoya Wada

Published May 3, 2010• 9 citations
Publisher

Abstract

We developed an optical input module with a superconducting single-flux-quantum (SFQ) circuit for application of ultrafast photonic networks in the near future. The optical input module, consisting of a built-in photodiode (PD) with a coplanar waveguide transmission line, was fabricated on an InP substrate and flip-chip bonded with the SFQ circuit on a Si substrate. The fabricated PD showed photosensitivities of more than 0.2 A/W for the wavelength range 1480 to 1530 nm at 4.2 K. SFQ pulses were generated by less than 1 mW optical pulse input.

DOI
10.1063/1.3428370

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We developed an optical input module with a superconducting single-flux-quantum (SFQ) circuit for application of ultrafast photonic networks in the near future. The optical input module, consisting of a built-in photodiode (PD) with a coplanar waveguide transmission line, was fabricated on an InP substrate and flip-chip bonded with the SFQ circuit on a Si substrate. The fabricated PD showed photosensitivities of more than 0.2 A/W for the wavelength range 1480 to 1530 nm at 4.2 K. SFQ pulses were generated by less than 1 mW optical pulse input.
We developed an optical input module consisting of built-in metal-semiconductor-metal photodiodes (MSM-PDs) and co-planar waveguide transmission lines fabricated on an InP substrate, which is flip-chip bonded with a single-flux-quantum (SFQ) circuit fabricated on a Si substrate. To improve photosensitivity of the MSM-PD for a wavelength above 1530 nm at 4 K, we tested the MSM-PDs made of lattice mismatched In1-xGaxAs films on InP substrates. By employing In1-xGaxAs with x=0.44, an apparent reduction of photosensitivity for a wavelength above 1530 nm was suppressed. We also tested newly designed DC/SFQ converters with higher input current sensitivities. The observed current sensitivity was improved to 41 μA, while that in the conventional DC/SFQ converter was 140 μA.
A superconductive single flux quantum (SFQ) digital integrated circuit with an optical data input has been demonstrated at the system level of 40 Gbit/s for the first time. A uni travelling carrier photodiode (UTC-PD) and an SFQ circuit chip, on which 40 Gbit/s I/O interfaces were integrated, were packaged on a cold stage (4–6 K) of a cryocooler system. The UTC-PD's output was connected to an input port of the SFQ circuit with a Cu coaxial cable. From room temperature, a 40 GHz clock was supplied to the SFQ circuit while 40 Gbit/s optical data were supplied to the UTC-PD. The SFQ circuit operated correctly with the optical 40 Gbit/s data. The measured bit error rate was less than 10−13 for 1.2 mW optical PRBS 7 input at 40 Gbit/s.
Single flux quantum (SFQ) circuits and optical circuits are expected to be used in next-generation integrated circuits. This study investigates basic technologies for integrating optical circuits with SFQ circuits to exploit the advantages of both technologies. We calculated, designed and evaluated metal-clad waveguides, which can be fabricated by the ISTEC standard process (STD2). Light propagates along an 830-μm-long waveguide with a propagation loss of 16 dB/mm. We also designed and evaluated an optical-electrical (O-E) converter that uses a Josephson junction, which can be fabricated by the same process used to fabricate the SFQ circuits. When an optical signal with a peak power of 1.15 mW at 1.548 μm is input, the Josephson O-E converter generates SFQ pulses.
We report on the demonstration of the error-free operation of optical-to-electrical (O/E) signal converter based on superconducting nanowires with single-flux-quantum circuits. Optical input pulses were generated by the pulse pattern generator and the optical modulator, and the error rate of the output signals was measured. For a 300-nm-wide device with active area of 15×15 μm2, correct O/E conversion was confirmed with the error-rate of less than 10-6at the maximum repetition frequency of 120 MHz. The optical energy consumption per pulse was one order of magnitude lower than those of conventional semiconductor photodiodes.