Tailorable Stimulated Brillouin Scattering in Nanoscale Silicon Waveguides (1301.7311v1)

Abstract: While nanoscale modal confinement radically enhances a variety of nonlinear light-matter interactions within silicon waveguides, traveling-wave stimulated Brillouin scattering nonlinearities have never been observed in silicon nanophotonics. Through a new class of hybrid photonic-phononic waveguides, we demonstrate tailorable traveling-wave forward stimulated Brillouin scattering in nanophotonic silicon waveguides for the first time, yielding 3000 times stronger forward SBS responses than any previous waveguide system. Simulations reveal that a coherent combination of electrostrictive forces and radiation pressures are responsible for greatly enhanced photon-phonon coupling at nano-scales. Highly tailorable Brillouin nonlinearities are produced by engineering the structure of a membrane-suspended waveguide to yield Brillouin resonances from 1 to 18 GHz through high quality-factor (>1000) phonon modes. Such wideband and tailorable stimulated Brillouin scattering in silicon photonics could enable practical realization of on-chip slow-light devices, RF-photonic filtering and sensing, and ultra-narrow-band laser sources by using standard semiconductor fabrication and CMOS technologies.

• The paper demonstrates a novel membrane-suspended waveguide that tailors SBS interactions with nonlinearities 3000 times stronger than conventional systems.
• It employs precise control of photonic and phononic modes to enable wideband phonon emissions from 1 to 18 GHz with high Q-factors over 1000.
• The work paves the way for CMOS-compatible silicon photonic systems capable of advanced RF and signal processing applications.

Tailorable Stimulated Brillouin Scattering in Silicon Nanophotonics

The research paper investigates the realization of traveling-wave forward stimulated Brillouin scattering (SBS) nonlinearities in silicon nanophotonic waveguides, a significant advancement for silicon-based optomechanical systems. This work introduces a novel hybrid photonic-phononic waveguide architecture that enables strong photon-phonon coupling, significantly surpassing the constraints of traditional waveguide systems.

The advancement hinges on employing a membrane-suspended waveguide design that removes the phonon-loss pathway inherent to conventional silicon-on-insulator waveguides. The unique geometry offers independent control over photonic and phononic modes, allowing for meticulous tailoring of SBS interactions. Distinctively, the Brillouin nonlinearities demonstrated are 3000 times stronger than those previously observed in other waveguides, marked by a blend of nano-enhanced electrostrictive forces and boundary-induced radiation pressures.

Results and Key Findings

• Enhanced Nonlinearities: The experimental results reveal Brillouin nonlinearities with a magnitude significantly superior to those in prior systems, facilitated by a combination of material-induced electrostrictive forces and boundary-induced radiation pressure.
• Wideband Phonon Emission: The system supports exceptionally wide-band and high-frequency coherent phonon emissions. The structural tuning of phononic resonances from 1-18 GHz, with high Q-factors (>1000), facilitates customizable nonlinear optical susceptibilities.
• Remarkable Efficiency: This hybrid system surpasses the capabilities of cavity optomechanical structures by achieving efficient wideband operations essential for various radiofrequency (RF) and photonic signal processing applications. The research also demonstrates the potential for Brillouin nonlinearities to serve as the dominant mechanism in silicon waveguides, given the gain coefficient being thousands of times larger than those observed in other implementations.

Theoretical Implications and Future Directions

Conceptually, the research underscores the potential to extend the interaction of light and sound in silicon photonics via Brillouin processes, thereby enriching the field of integrated photonics and enabling novel functionalities. The paper offers theoretical insights into the coupling phenomena facilitated by dense optical force distributions within nanoscale waveguides, reshaping the frequency dependence of Brillouin coupling.

Practical Implications and Technological Impact

The practical implications of these findings are profound, paving the way for enhanced CMOS-compatible silicon photonic systems capable of executing advanced signal processing tasks, including pulse compression, waveform synthesis, coherent frequency comb generation, and more. The paper suggests that future developments may further integrate these improved Brillouin-based systems with other on-chip technologies such as micro-electromechanical systems (MEMS).

Given the controlled nature of phononic emissions in such developed systems, the possibilities for coherent information transduction in silicon photonics are expanded. Continued advancements inspired by this research will likely see the increased development of compact, efficient, and versatile optical devices for various applications, with a particular emphasis on the seamless integration of optomechanical and photonic functionalities in modern technology.

In summary, the findings represent a crucial stride toward optimizing and applying silicon-based traveling-wave Brillouin interactions within a chip-scale framework, pointing toward a diverse array of new technological implementations in the field of photonics and beyond.