On-chip Brillouin Amplifier in Suspended Lithium Niobate Nanowaveguides

TL;DR

This paper demonstrates a high-gain on-chip Brillouin amplifier in suspended lithium niobate nanowaveguides, highlighting the material's potential for integrated nonlinear photonics and signal processing.

Contribution

It reports the first record-high Brillouin gain in suspended TFLN nanowaveguides and systematically characterizes the anisotropic Brillouin gain coefficients.

Findings

Achieved a Brillouin gain coefficient of 129.5 m$^{-1}$W$^{-1}$

Demonstrated Brillouin frequency tuning via pump frequency and temperature

Realized a record-high 8.5 dB Brillouin amplifier gain

Abstract

Thin film lithium niobate (TFLN) has emerged as a leading material platform for integrated nonlinear photonics, enabling transformative applications such as broadband Kerr soliton microcomb and high-speed electro-optic modulation. While stimulated Brillouin scattering has been numerically proposed in TFLN, achieving sufficient gain remains challenging due to the requirement for the simultaneous low optical and mechanical losses of the device. In this work, we systematically characterize the angle-dependence of Brillouin gain coefficients in x-cut membrane-suspended TFLN nanowaveguides, taking into account the anisotropy of the photoelastic coefficients in lithium niobate. We report a Brillouin gain coefficient of 129.5 m$^{-1}$W$^{-1}$ and further demonstrate the Brillouin frequency tuning through variations in either pump frequency or chip operating temperature. Based on the suspended TFLN nanowaveguide, by optimizing the confinement of both photonic and phononic modes, we have achieved a Brillouin amplifier with a record-high gain of 8.5 dB. This result not only validates the feasibility of strong guided Brillouin interaction using suspended TFLN nanowaveguides, but also paves the way for novel on-chip sensing and signal processing applications.