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IEEE Transactions on Applied Superconductivity

Design and performance of superconducting circuits for LiNbO/sub 3/ optical modulator and switch

Keiji Yoshida, Y. Kanda, H. Yoshihara, Haruichi Kanaya, S. Shinkai, M. Ishitobi

Published Jun 1, 2003• 10 citations
Publisher

Abstract

The design and performance of a LiNbO/sub 3/ optical modulator and switch, which employ superconducting circuits, have been studied. Based on a novel design method of the booster circuit using superconducting coplanar waveguide transmission lines, we designed a voltage amplifier with center frequency of 10 GHz, bandwidth of 5 MHz, and the voltage gain of 33 dB using an electromagnetic wave simulator. We also designed a high speed optical switch combining optical directional coupler and Mach-Zehnder interferometer. A preliminary experiment with YBCO electrode on MgO substrate flip-chip-bonded on LiNbO/sub 3/ optical waveguide has been made.

DOI
10.1109/tasc.2003.814142

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The design and performance of a LiNbO/sub 3/ optical modulator and switch, which employ superconducting circuits, have been studied. Based on a novel design method of the booster circuit using superconducting coplanar waveguide transmission lines, we designed a voltage amplifier with center frequency of 10 GHz, bandwidth of 5 MHz, and the voltage gain of 33 dB using an electromagnetic wave simulator. We also designed a high speed optical switch combining optical directional coupler and Mach-Zehnder interferometer. A preliminary experiment with YBCO electrode on MgO substrate flip-chip-bonded on LiNbO/sub 3/ optical waveguide has been made.
The performance of a LiNbO/sub 3/ optical modulator employing superconducting electrodes as a transmission line for a traveling-wave signal has been studied theoretically as well as experimentally. In the case of velocity matching between signal and optical waves using a shielding plane on top of a coplanar waveguide, numerical calculations of the attenuation constants of both superconducting and normal-conducting transmission lines indicate that the performance of the optical modulator can be far superior to that using normal-metals with respect to the figure of merit of bandwidth/driving-voltage. Microwave operation of a velocity-matched traveling-wave-type optical modulator with superconductor electrodes (NbN) has been successfully demonstrated. In the frequency range between dc and 26.5 [GHz] it is shown that the obtained modulation depth is in good agreement with the theoretically expected one.
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.
This paper reports the design, fabrication, and measurements of optically tunable superconducting microwave resonators and delay lines. The devices are comprised of superconducting coplanar waveguide (CPW) transmission lines fabricated from a 100 nm-thick YBCO film, interrupted by 3- and 5-m YBCO meander structures of the same thickness on top of an LAO substrate. The CPW is tested at 77 K up to a frequency of 50 GHz, where it exhibits a transmission loss of about 0.12 dB/mm. The measurements are done in a cryogenic microwave probe station, where all the calibrations have been performed at 77 K. It has been observed that the resonance frequencies of the superconducting resonators can be changed by more than 2 GHz under the optical illumination at a wavelength of 1550 nm. The delay lines also exhibit a phase retardation of up to 90 at the same operating conditions.
Power divider is a useful device that divides the power of signal into different subpowers at a certain ratio. The superconducting power divider plays an important role in various superconducting quantum computing circuits and superconducting microwave photon detectors. Therefore, in this paper we investigate how to design and prepare a typical coplanar waveguide superconducting microwave power divider. The parameters are designed by using the odd-even mode method to analyze the transport features of a three-port microwave network. Specifically, the microwave transport properties of the device with a center frequency of 5 GHz and 3 dB power division ratio are simulated. Then, the designed aluminum coplanar waveguide superconducting power divider on silicon is prepared by micro-processing technology and experimentally tested at low temperature. It is shown that the measurement results are consistent with the design parameters. It is noted that the center frequency of the actually prepared power divider is measured to be about 5.25 GHz, which is slightly different from the result of the design and simulation. This difference is probably due to the following main reasons. Firstly, the limited precision of the micromachining process is caused by the fact that the fabricated quarter-wave impedance matching line is etched incompletely, leading the length of the impedance matching line to be shortened. As a consequence, the frequency of the prepared power divider is slightly higher. Secondly, the simulation software is not designed specially for superconducting device simulations, thereby yielding the design parameters slightly different from those of the fabricated superconducting devices. Additionally, a series of attenuations has been used in the experimental test system of the superconducting microwave power dividers for reducing the various noises. This causes the input test signal to weaken, thus the reflected signal turns significantly small. Therefore, none of the S11 parameters of the device can be effectively measured. Finally, neither of S21 and S31 parameters measured in the experiment is the predicted –3 dB, which is mainly due to the imperfections in the welding between SMA connectors and high-frequency transmission lines, and the spot welding between high-frequency transmission lines and power divider samples, and also due to the discontinuities of the high-frequency transmission line and the power divider and so on. All these factors can yield the tested insertion loss of the device. Hopefully, the method in this work can be extended to designing and preparing other passive superconducting microwave devices.
This paper presents the design and simulation of a thin-film on-chip superconducting rat-race and quadrature branch-line coupler for circuit quantum electrodynamics. These couplers are designed at a center frequency of 6GHz using coplanar waveguide technology using a thin film of niobium or aluminum on sapphire substrates. The electrical connections are made between the ground using aluminum air bridges. The insertion losses to the through and coupled ports of rat-race and quadrature coupler are 3.1dB. The quadrature and rat-race couplers offer a wide bandwidth of 2GHz and 3GHz, respectively. A spectral shift of around 400MHz is observed in these couplers when operation is shifted from room temperature to the cryogenic regime. The simulated results have been discussed and analyzed.
In this paper, we present the design of a resonance phase-matched Josephson travelling-wave parametric amplifier that have a 12 GHz 3 dB-bandwidth centred near 10 GHz. Our design utilises a unilateral planar circuit structure which requires only a single layer of thin superconductor film deposited on a supporting substrate to reduce the fabrication complexity. The nonlinear medium of the device is provided by a series of Josephson junctions embedded in a coplanar waveguide with integrated shunt capacitor, and the dispersion of the transmission line is controlled by quarter wavelength resonators coupled capacitively to the feedline. Here, we describe in detail the electromagnetic designs of the various components of the amplifier, and the coupled-mode equations model that governs the three-wave mixing process. We extract the required circuit parameters of the amplifier through electromagnetic modelling, and determine the parametric gain-bandwidth product of the amplifier using an analytical model. Finally, we discuss the various design aspects that affect the overall performance of the amplifier.