Study on Broadband Optical Modulator with Superconducting Transmission Line

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We have studied a long voltage optical modulator employing high Tc superconducting resonant-type electrodes for use in the sub-carrier optical transmission system in which microwave signals are carried by intensity modulated light-wave. It is shown that microwave modulation of light-wave can be made efficient by using superconducting electrodes with high Q-factor. A preliminary experiment using LiNbOィイD23ィエD2 (LN) optical modulator with YBaィイD22ィエD2CuィイD23ィエD2OィイD2xィエD2 (YBCO) electrode demonstrates dc and microwave modulation of the optical wave.1. The design of resonant type optical modulators with impedance circuits in presented, and YBCO thin films on MgO substrate were employed as the electrodes. It is shown by numerical calculation that the modulation efficiency increases when high Q superconductors are used as the electrodes.2. We present a preliminary experiment on the optical modulator, which was realized by flip-chip bonding of LN and MgO substrates. Based on the design and calculation, modulation experiments were carried out at low temperatures. It was demonstrated that the optical modulator with high Tc superconducting electrode by the flip-chip bonding method operated effectively.