Cascaded traveling wave electrodes designed for group velocity matching in electro-optic modulation

Abstract

Group velocity and impedance matches are prerequisites for high-speed Mach-Zehnder electro-optic modulators. However, not all platforms can realize match conditions, restricting high-speed modulation in many practical platforms. Here we propose and demonstrate a general method to satisfy the group velocity and characteristic impedance matches by cascading fast-wave and slow-wave traveling wave electrodes on a thin-film lithium-niobate-on-insulator platform with a silica cladding. The effective group velocity can be flexibly adjusted by changing the ratio of fast-wave and slow-wave traveling wave electrodes. The radio frequency signal insertion loss at the boundary of the slow-wave and fast-wave electrodes is less than 0.1 dB. In addition, for a modulator of 6000 μm length, our simulation indicates an electro-optic response of over 100 GHz, surpassing what can be achieved with purely slow-wave or fast-wave electrodes that lack matching conditions.Our results will open many opportunities for high-speed electro-optic modulators in various platforms.