Acousto-optic modulation using high-order optical modes in hybrid thin-film lithium niobate straight waveguides

Integrated acousto-optic modulators (AOMs) supporting high-order optical modes have enlarged the functionality of photonic integrated circuits. In this work, non-collinear straight waveguide AOMs supporting pure first-order and second-order transverse electric modes (TE₁₀, TE₂₀) are experimentally presented based on a chalcogenide-loaded TFLN wafer. By measuring the evolution of acousto-optic interactions in the hybrid multimode waveguide, the TE₀₀ device achieves half-wave-voltage-length product of 0.93 V·cm under the RF input power of 15 dBm, surpassing TE₁₀ or TE₂₀ counterpart. Without considering microwave-to-acoustic conversion, TE₁₀ has comparable phase modulation capability compared with TE₀₀. Experimental demonstration of TE₁₀ and TE₂₀ participating in straight-waveguide acousto-optic modulation paves the way for high-order optical modes to regulate and control modulation characteristics.