Thin‐Film Lithium Niobate Traveling‐Wave Modulators with Embedded DC‐Bias Electrode

Abstract High‐performance electro‐optic modulators based on thin‐film lithium niobate have been widely studied recently. Owing to the characteristics of a Mach‐Zehnder modulator structure, a specific direct‐current (DC) bias is normally needed to ensure optimal operating conditions for modulation. Common approaches for bias control suffer from drawbacks such as additional phase shifters, high power consumption, and low tuning speed. In this work, an effective electrode structure we proposed and demonstrated, which enables electro‐optic DC‐bias tuning of nearly‐zero power consumption. The proposed structure adopts a layered traveling‐wave electrode design without introducing any additional optical elements and compromising any modulation performances. The fabricated devices exhibit a halfwave‐voltage‐length product of 2.3 Vcm and an ultra‐wide bandwidth well exceeding 67 GHz. The DC‐bias tuning capability is also verified through measuring the optical transmission at low to high frequencies by driving the microwave modulation and DC‐bias electrodes separately and simultaneously. Data transmissions up to 224 Gbps data rate are also performed using the fabricated device at various wavelengths and bias voltages. The demonstrated embedded electrode structure offers a unprecedent solution on thin‐film lithium niobate Mach‐Zehnder modulators for achieving DC‐bias control with a compact device size, low power consumption, and fast tuning speed.