Observation of Stimulated Brillouin Scattering in Silicon Nitride Integrated Waveguides

Abstract

Silicon nitride (Si3N4) has emerged as a promising material for integrated nonlinear photonics and has been used for broadband soliton microcombs and low-pulse-energy supercontinuum generation. Therefore understanding all nonlinear optical properties of Si3N4 is important. So far, only stimulated Brillouin scattering (SBS) has not been reported. Here we observe, for the first time, backward SBS in fully cladded Si3N4 waveguides. The Brillouin gain spectrum exhibits an unusual multi-peak structure resulting from hybridization with high-overtone bulk acoustic resonances (HBARs) of the silica cladding. The reported intrinsic Si3N4 Brillouin gain at 25 GHz is estimated as 7×10 −13 m/W. Moreover, the magnitude of the Si3N4 photoelastic constant is estimated as |p12| = 0.047 ± 0.004. Since SBS imposes an optical power limitation for waveguides, our results explain the capability of Si3N4 to handle high optical power, central for integrated nonlinear photonics. arXiv:1908.09815v1 [physics.optics]

Hybrid Integrated Semiconductor Lasers with Silicon Nitride Feedback Circuits

“…Stimulated Brillouin scattering (SBS) is another effect that can manifest as a nonlinear loss in the laser feedback circuit. This process is mediated by optoacoustic interactions in a medium, and has been observed in various waveguide platforms including silica [16], silicon [154], and silicon nitride [155]. The strength (or the intrinsic gain) of SBS is mainly dictated by the material properties, including refractive index, acoustic damping, and photoeleastic constant, as well as the optoacoustic overlap of the waveguiding structure [156].…”

Coupling of light and mechanics in a photonic crystal waveguide

“…A measurement of the photo-elastic constant for Si3N4 can be found in ref. 49. Also note that G PE ∝ n 4 , with the ratio of Si3N4 (as here) to Si (as in ref.…”

Hybrid integrated photonics using bulk acoustic resonators

“…Although within the last decade, silicon photonics has transitioned from laboratory-based research into commercial products used in data centers, major efforts are still underway with regards to silicon nitride (Si 3 N 4 ) photonic devices 1 . The Si 3 N 4 platform has attracted intense efforts due to its wide transparency window from the visible to mid-infrared, ultralow linear losses 1 , absence of two-photon absorption in the telecommunication band, large Kerr nonlinearity χ (3) , small Brillouin gain 2 , and flexibility for waveguide geometric dispersion engineering 3 . Silicon nitride has been a popular material of choice for dissipative Kerr soliton microcomb generation 4 .…”

“…Likewise, recently emerged platforms such as spatiotemporal-modulation-based optical nonreciprocity 15 and topological optical bandstructures 16,17 require GHz-rate modulation within optical microresonators, which poses stringent requirements on the cross-talk and size. However, due to the inversion symmetry, and thus the lack of χ (2) nonlinearity, it is challenging to electrically modulate the refractive index of Si 3 N 4 . Traditionally, the thermo-optical effect is employed to fulfill the tuning requirement 18,19 .…”

“…These drawbacks make it incompatible with large-scale integration and cryogenic applications 20 . Although hybrid integration with various electrooptical materials, e.g., graphene 21 , lead zirconate titanate (PZT) 22 , lithium niobate (LiNbO 3 ) 23 , and monolayer WS 2 24 , has made significant progress, there are still remaining challenges related to Complementary Metal Oxide Semiconductor (CMOS) compatibility, fabrication complexity, optical loss, and dispersion engineering. To fully utilize the maturity and advantages of Si 3 N 4 photonics, new tuning mechanisms that retain the original optical properties (e.g., waveguide low-loss and dispersion) are needed.…”