高性能馬赫詹德行波電極型鈮酸鋰薄膜電光調制器

Abstract

隨著光通訊系統傳輸速率不斷提升，具備高頻寬、低功耗與高調制效率之電光調制器需求日益增加。本研究提出一種基於薄膜型鈮酸鋰 (Lithium Niobate on Insulator,LNOI) 之新型馬赫詹德調制器設計，採用狹縫波導 (Slot Waveguide) 結構，並於上方包覆高介電常數材料鈦酸鋇 (Barium Titanate, BTO) 與二氧化矽 (Silicon dioxide, SiO2) 形成複合包覆層，結合下潛式金屬電極以增強電場與光場之交互作用，藉此提升電光調制效率並拓展頻寬。 本研究首先透過 Lumerical 模擬平台進行模態分析與電場模擬，萃取有效折射率與相位變化，進一步計算調制效率 (𝑉π𝐿) 為 0.999 V·cm。接著以 RLGC 模型與傳輸線理論推導射頻參數，分析結構於 1–200 GHz 頻段內之阻抗匹配、傳播速度匹配與傳輸損耗，並量化射頻損耗對頻寬限制之影響。此外，藉由 INTERCONNECT 建立等效電路模型，模擬 NRZ 與 PAM4 調制格式下之眼圖， 評估其高速傳輸表現與消光比 (Extinction Ratio, ER)。 模擬結果顯示，本設計於 3 mm 調制長度下可達 191 GHz 的電光頻寬，並於 448 Gbps 資料速率下仍具良好眼圖開口，展現極佳的頻寬潛力與調制品質。與其他文獻中典型 LNOI 結構比較，本研究設計同時具備低 𝑉π𝐿、高頻寬與可接受之傳輸損耗，為未來應用於資料中心與矽光子平台整合之高效能電光調制器提 供可行方案。

With the increasing demands for high-speed and high-efficiency data transmission in optical communication systems, lithium niobate (LN)-based electro-optic modulators have attracted significant attention due to their superior modulation bandwidth and low drive voltage enabled by the Pockels effect. In this work, we propose and numerically demonstrate a high-performance thin-film lithium niobate (LNOI) Mach-Zehnder modulator (MZM) incorporating a slot waveguide structure, a composite cladding layer composed of high-permittivity Barium Titanate (BTO) and silicon dioxide (SiO2), and a sunken electrode configuration. Through multiphysics simulations using the Lumerical platform, we extract the phase modulation efficiency and determine a half-wave voltage-length product (𝑉π𝐿) of 0.999 V·cm. The RLGC transmission line model is then applied to analyze frequency- dependent microwave properties-including impedance, group velocity, and attenuation- across the 1–200 GHz range. We quantify both the velocity mismatch and microwave loss limitations on modulation bandwidth. Subsequently, compact model parameters are used in INTERCONNECT to construct a complete modulator circuit, and time- domain eye diagram simulations are performed for both NRZ and PAM4 signaling formats. The proposed design achieves a 3-dB EO bandwidth of 191 GHz for a 3-mm modulation length, with a clear eye opening observed at 112 Gbps under PAM4 modulation. Compared to representative state-of-the-art LNOI modulators in the literature, our device simultaneously exhibits a low 𝑉π𝐿 , wide bandwidth, and acceptable insertion loss, demonstrating strong potential for integration in future high- speed silicon photonics and data center applications.