Thin-Film Lithium Niobate Based Acousto-Optic Modulation Working at Higher-Order TE1 Mode

Acousto-optic modulation (AOM) is regarded as an effective way to link multi-physical fields on-chip. We propose an on-chip AOM scheme based on the thin-film lithium niobate (TFLN) platform working at the higher-order TE1 mode, rather than the commonly used fundamental TE0 mode. Multi-physical field coupling analyses were carried out to obtain the refractive index change of the optical waveguide (> 6.5x10(-10) for a single phonon) induced by the enhanced acousto-optic interaction between the acoustic resonator mode and the multimode optical waveguide. By using a Mach-Zehnder interferometer (MZI) structure, the refractive index change is utilized to modulate the output spectrum of the MZI, thus achieving the AOM function. In the proposed AOM scheme, efficient mode conversion between the TE0 and TE1 mode is required in order to ensure that the AOM works at the higher-order TE1 mode in the MZI structure. Our results show that the half-wave-voltage-length product (V pi L) is < 0.01 V & BULL;cm, which is lower than that in some previous reports on AOM and electro-optic modulation (EOM) working at the fundamental TE0 mode (e.g., V pi L > 0.04 V & BULL;cm for AOM, V pi L > 1 V & BULL;cm for EOM). Finally, the proposed AOM has lower loss when compared with EOM because the electrode of the AOM can be placed far from the optical waveguide.

Automated summary

This study proposes an on-chip acousto-optic modulation (AOM) scheme based on the thin-film lithium niobate platform, operating at the higher-order TE1 mode. Through the enhanced acousto-optic interaction, the refractive index change of the optical waveguide is utilized to modulate the output spectrum of the device. Efficient mode conversion between TE0 and TE1 modes is required for the proposed AOM scheme. The results demonstrate lower loss and a lower voltage-length product compared to previous reports on AOM and electro-optic modulation (EOM) at the fundamental TE0 mode.