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Design and Performance of LiNbO 3 Optical Modulator with a Superconducting Electrode

The performance of a LiNbO3 optical modulator with a superconducting electrode as the transmission line of 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 is far superior to that using normal metals with respect to the figure of merit of bandwidth/driving voltage. Microwave characteristics of a traveling-wave-type LiNbO3 optical modulator with a superconducting electrode (Nb) have been also studied experimentally in the temperature range from 300 K to 4.2 K. 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. The present results demonstrate the possible applications of superconducting electrodes to high-performance LiNbO3 optical modulators.