Nonreciprocal Inter-band Brillouin Modulation

TL;DR

This paper demonstrates a nonreciprocal light modulation device in silicon photonics using nonlocal acousto-optic scattering, achieving high isolation, broad bandwidth, and tunability, advancing integrated optical isolator technology.

Contribution

It introduces a novel nonlocal inter-band Brillouin scattering approach for nonreciprocal modulation with record bandwidths and tunability in silicon photonics.

Findings

Achieved up to 38 dB nonreciprocity with 37 dB single-sideband suppression.

Bandwidth exceeds 125 GHz, set by optical phase-matching.

Demonstrated wavelength tunability over 35 nm.

Abstract

Achieving nonreciprocal light propagation in photonic circuits is essential to control signal crosstalk and optical back-scatter. However, realizing high-fidelity nonreciprocity in low-loss integrated photonic systems remains challenging. In this paper, we experimentally demonstrate a device concept based on nonlocal acousto-optic light scattering to produce nonreciprocal single-sideband modulation and mode conversion in an integrated silicon photonic platform. In this process, a traveling-wave acoustic phonon driven via optical forces in a silicon waveguide is used to modulate light in a spatially separate waveguide through a linear inter-band Brillouin scattering process. We demonstrate up to 38 dB of nonreciprocity with 37 dB of single-sideband suppression. In contrast to prior Brillouin- and optomechanics-based schemes for nonreciprocity, the bandwidth of this scattering process is set through optical phase-matching, not acoustic or optical resonances. As a result, record-large bandwidths in excess of 125 GHz are realized, with potential for significant further improvement through optical dispersion engineering. Tunability of the nonreciprocal modulator operation wavelength over a 35 nm bandwidth is demonstrated by varying the optical pump wavelength. Such traveling-wave acousto-optic modulators provide a promising path toward the realization of broadband, low-loss isolators and circulators in integrated photonic circuits.