Development of high gain and broadband superconducting booster circuit for optical modulator

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The design and performance of a LiNbO3 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 10GHz, bandwidth of 5MHz, and the voltage gain of 33dB 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 LiNbO3 optical waveguide has been made. We designed the booster circuit with the meanderline 3-pole Chebyshev filter fabricated by a YBCO thin film on a MgO substrate with the dimension of 10[mm]×10[mm]. The YBCO electrode on MgO substrate was flip-chip bonded onto an optical waveguide in a LiNbO3 substrate, and was cooled down by a refrigerator. The comparison of the observed group delay of S11 (return loss) of the device and the simulation results. The observed data are in reasonable agreements with those expected from theory.