Stimulated Forward Brillouin Scattering in Subwavelength Silicon Membranes
arxiv(2024)
Abstract
On-chip Brillouin scattering plays a key role in numerous applications in the
domain of signal processing and microwave photonics due to the coherent
bidirectional coupling between near-infrared optical signals and GHz mechanical
modes, which enables selective amplification and attenuation with remarkably
narrow linewidths, in the kHz to MHz range. Subwavelength periodic
nanostructures provide precise control of the propagation of light and sound in
silicon photonic circuits, key to maximize the efficiency of Brillouin
interactions. Here, we propose and demonstrate a new subwavelength waveguide
geometry allowing independent control of optical and mechanical modes. Two
silicon lattices are combined, one with a subwavelength period for the light
and one with a total bandgap for the sound, to confine optical and mechanical
modes, respectively. Based on this approach, we experimentally demonstrate
optomechanical coupling between near-infrared optical modes and GHz mechanical
modes with with 5-8 MHz linewidth and a coupling strength of GB = 1360 1/(W m).
A Stokes gain of 1.5 dB, and anti-Stoke loss of -2 dB are observed for a 6
mm-long waveguide with 35.5 mW of input power. We show tuning of the mechanical
frequency between 5 and 8 GHz by geometrical optimization, without loss of the
optomechanical coupling strength.
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