Guided-acoustic stimulated Brillouin scattering in silicon nitride photonic circuits

Abstract

Coherent optomechanical interaction known as stimulated Brillouin scattering (SBS) can enable ultrahigh resolution signal processing and narrow-linewidth lasers. SBS has recently been studied extensively in integrated waveguides; however, many implementations rely on complicated fabrication schemes. The absence of SBS in standard and mature fabrication platforms prevents its large-scale circuit integration. Notably, SBS in the emerging silicon nitride (Si 3 N 4 ) photonic integration platform is currently out of reach because of the lack of acoustic guidance. Here, we demonstrate advanced control of backward SBS in multilayer Si 3 N 4 waveguides. By optimizing the separation between two Si 3 N 4 layers, we unlock acoustic waveguiding in this platform, potentially leading up to 15× higher Brillouin gain coefficient than previously possible in Si 3 N 4 waveguides. We use the enhanced SBS gain to demonstrate a high-rejection microwave photonic notch filter. This demonstration opens a path to achieving Brillouin-based photonic circuits in a standard, low-loss Si 3 N 4 platform.

High performance programmable integrated microwave photonic filters

“…Brillouin scattering in the waveguide is characterized by the gain parameter (G (SBS) ) which is defined by [135] G SBS = e g B PpL e↵…”

“…where g B is the Brillouin gain coefficient, P p is the pump power, and L e↵ is the effective length of the waveguide that can be calculated with [135]…”

“…Although Brillouin-based MWP filter has been widely studied in optical fibers [149]- [152], recently there has been growing interest in harnessing SBS in an integrated photonic platform [97], [135], [153]- [155]. The ability of inducing SBS in photonic chip opens new paradigm of Brillouin-based MWP filter that can exhibits tens of MHz of narrow bandwidth in chip-scale photonic device as opposed to the long length of optical fibers.…”

“…The works are limited to the usage of observed SBS in symmetric double-stripe (SDS) silicon nitride material [135] and the proof-of-concept of this platform when combined with existing integrated optical components to synthesize filtering function.…”

“…The ability to precisely guide the acoustic wave in SDS silicon nitride waveguides can provide the enhancement of SBS in these waveguides. The detail observation of SBS in silicon nitride is beyond the scope of this thesis and interested reader can refer to [135].…”