基于薄膜铌酸锂异质集成硫系玻璃的中红外电光调制器的仿真研究OA

The mid-infrared(MIR)3～5 μm band spans both an atmospheric transmission window and the molecular fingerprint region,enabling important applications in free-space optical communications,spectroscopic sensing,and thermal imaging.High-speed,low-loss modulators in this band are essential for advancing MIR photonic integrated systems,yet remain challenging to realize.Conventional platforms such as silicon,silicon nitride,aluminum nitride,and gallium arsenide often suffer from carrier absorption,thermo-optic effects,or limited electro-optic(EO)bandwidth in the MIR,making it difficult to simultaneously achieve high modulation efficiency and broad bandwidth.Thin-film lithium niobate(LNOI),featuring a wide transparency window and a strong Pockels effect,is a promising platform for ultrahigh-speed EO modulation;however,commercial LNOI wafers typically incorporate a SiO2 buried-oxide(BOX)layer whose pronounced absorption in the MIR band introduces excess propagation loss,thereby limiting MIR device performance and system-level integration. In this work,the BOX-absorption-induced loss bottleneck was addressed by aiming to develop a low-loss,high-efficiency,and ultrabroadband MIR EO modulator compatible with standard commercial LNOI wafers.A heterogeneously integrated LNOI/chalcogenide-glass(ChG)platform was proposed and numerically investigated.The key idea is to employ refractive-index-tunable ChG as an optical guiding layer,with a ChG strip waveguide integrated on the LNOI surface.This design pulls the optical mode upward and markedly reduces modal overlap with the SiO2 BOX layer.This mode-engineering strategy suppresses MIR absorption loss while introducing additional degrees of freedom-via the ChG refractive index and waveguide geometry-for co-optimizing propagation loss,modulation efficiency,and EO bandwidth. A Mach-Zehnder modulator was designed on a representative X-cut LNOI/SiO2/Si stack,consisting of a～900-nm-thick lithium niobate film,a～4.7-μm-thick SiO2 BOX layer,and a～500-μm-thick silicon substrate.The device incorporated 1×2 multimode-interference splitters/combiners and a push-pull traveling-wave electrode phase shifter.A multiphysics co-simulation framework was employed for joint optical-RF optimization:on the optical side,the ChG refractive index and key geometric parameters were systematically swept to tailor the modal distribution and minimize propagation loss;on the RF side,electromagnetic simulations were used to optimize electrode dimensions and spacing,enabling optical-microwave group-index matching,reduced microwave attenuation,and favorable impedance matching,thereby enhancing the EO 3 dB bandwidth. After comprehensive optimization,the proposed device achieves,at 4.1 μm,a low propagation loss of 0.67 dB/cm,a half-wave voltage-length product of 14.7 V-cm,and an EO 3 dB bandwidth exceeding 110 GHz,demonstrating a compelling combination of low loss,high efficiency,and ultrabroad bandwidth.Overall,these results establish refractive-index-engineered ChG-assisted mode engineering as an effective route to mitigate BOX absorption on commercial LNOI wafers.Compared with alternative approaches relying on deep etching,BOX removal,or substrate re-engineering,this hetero-integration strategy achieves substantial performance improvements with low process invasiveness,offering enhanced platform compatibility and scalability.These findings provide a transferable design paradigm for compact,high-performance MIR EO modulators and may facilitate further advances in high-speed on-chip modulation for MIR communications,sensing,and quantum information processing.