Stimulated Brillouin Scattering (SBS) is a third-order nonlinear effect involving the optically induced excitation of acoustic waves [1]. Several new materials have been proposed to harness SBS on-chip and enable strong SBS within integrated photonic devices. Recently, lithium tantalate (LiTaO3, or LT) has emerged as a promising platform for photonic applications due to its mechanical anisotropy, which enables effects such as piezoelectricity and pyroelectricity, along with low-cost scalable manufacturing and a high optical damage threshold [2]. In this work, we report the first measurement of backward SBS in a lithium tantalate on insulator (LTOI) integrated waveguide. Additionally, numerical simulations are presented to support the experimental data.

Our sample follows the “flower-shape” design from [3]. Measurements were taken on an X-cut lithium tantalate ridge waveguide with a width of 600 nm, a thickness of 600 nm, and a length of 5 mm. The waveguide was designed to confine only the fundamental transverse electric (TE) and transverse magnetic (TM) optical modes. A pump-and-probe scheme [3] was used to measure the Brillouin spectrum for co- and cross-polarized backward SBS at θx = 60°. We observed two Brillouin peaks between 7 GHz and 8 GHz for the co-polarized configuration. Based on finite element method (FEM) simulations performed using COMSOL Multiphysics for both optical and mechanical modes, we identified similar peaks in a simplified waveguide model, mechanically clamped at the lower LT-SiO2 interface and oriented at 62°. Despite it’s simplification, this model still provides valuable insight into the actual mechanical modes supported by the full structure.  In conclusion, we experimentally observed backward SBS in an LTOI ridge waveguide. This finding offers new insights into SBS behavior in anisotropic platforms.

Funding

This work was supported by São Paulo Research Foundation (FAPESP) through grants 23/01206-3, 19/14377-5, 18/15577-5, 18/15580-6, 18/25339-4, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) grant 409626/2022-8. Supported by Harvard University Dean’s Competitive Fund for Promising Scholarship.

References

[1] G. S. Wiederhecker, P. Dainese, T. P. M. Alegre, “Brillouin optomechanics in nanophotonic structures”. APL Photonics 4, 071101 (2019).

[2] C. Wang et al. “Lithium tantalate photonic integrated circuits for volume manufacturing”. Nature 629, 784–790 (2024).

[3] C. C. Rodrigues et al. “Cross-Polarized Stimulated Brillouin Scattering in Lithium Niobate Waveguides”. Physical Review Letters 134, n. 11, p. 113601 (2025).