Interaction between light and highly confined hypersound in a silicon photonic nanowire (1407.4977v1)

Abstract: In the past decade, there has been a surge in research at the boundary between photonics and phononics. Most efforts centered on coupling light to motion in a high-quality optical cavity, typically geared towards observing the quantum state of a mechanical oscillator. It was recently predicted that the strength of the light-sound interaction would increase drastically in nanoscale silicon photonic wires. Here we demonstrate, for the first time, such a giant overlap between near-infrared light and gigahertz sound co-localized in a small-core silicon wire. The wire is supported by a tiny pillar to block the path for external phonon leakage, trapping $\mathbf{10} \; \textbf{GHz}$ phonons in an area below $\mathbf{0.1 \; \boldsymbol\mu}\textbf{m}^{\mathbf{2}}$. Since our geometry can be coiled up to form a ring cavity, it paves the way for complete fusion between the worlds of cavity optomechanics and Brillouin scattering. The result bodes well for the realization of low-footprint optically-pumped lasers/sasers and delay lines on a densely integrated silicon chip.

• The paper establishes enhanced photon-phonon interaction in nanoscale silicon wires through increased mode overlap, achieving superior coupling metrics.
• The study employs precise mode confinement using a small pillar to isolate 10 GHz phonons within a sub-0.1 µm² area, effectively reducing leakage.
• The paper demonstrates potential for miniaturized photonic circuits by validating gain experiments with a Brillouin nonlinearity of 3218 W⁻¹m⁻¹ and a mechanical quality factor of 306.

Interaction between Light and Hypersound in Silicon Photonic Nanowires: An Expert Review

This paper explores a significant advancement in the coupling of light and sound (phonons) within nanoscale silicon photonic wires. It reveals the theoretical prediction and experimental confirmation of a strong interaction between near-infrared light and gigahertz frequencies of sound, confined in a small-core silicon waveguide. The authors demonstrate that such a strong overlap enables a substantial photon-phonon coupling, leading to potential applications in integrated optomechanics and Brillouin scattering devices on silicon chips.

Summary of Key Contributions

The research emphasizes several key points:

1. Enhanced Photon-Phonon Interaction: Utilizing nanoscale silicon waveguides, the paper reports an enhanced photon-phonon coupling that significantly surpasses previous achievements. This enhancement arises due to an increased overlap between optical modes and the hypersonic acoustic modes, confined within the silicon core.
2. Efficient Mode Confinement: The structure of the silicon wire, supported by a small pillar, effectively confines 10 GHz phonons within an area smaller than 0.1 µm², thereby reducing phonon leakage and enhancing interaction strength.
3. Implications for Photonic Circuits: The physical configuration allows the geometry to be coiled to form ring cavities, indicating progress towards creating compact silicon-based laser and optical delay lines with low power consumption and high integration density.
4. Performance Metrics: Through gain and cross-phase modulation experiments, the paper measures a Brillouin nonlinearity parameter of 3218 W⁻¹m⁻¹ and a mechanical quality factor Q_m of 306, demonstrating a phonon lifetime of approximately 5.3 ns. These parameters suggest effective control over the optomechanical interactions which are vital for the envisioned photonic applications.

Implications and Future Directions

The paper contributes substantially to integrated photonic platforms, marrying the concepts of optomechanics with Brillouin scattering, thus enhancing the possibilities for future photonic computing and communication technologies. The advancement suggests a path toward new silicon photonic devices with dramatically improved performance metrics.

Future developments may focus on optimizing the silicon structures to further reduce phonon losses and achieve higher quality factors. Strategies could include employing asymmetric phononic modes or modifying the waveguide design, which would mitigate pillar-induced phonon leakage. Additionally, integrating this technology with existing CMOS platforms could advance the potential for commercial applications in data communication and signal processing industry.

This research exemplifies the trend of using engineering geometry to manipulate fundamental interactions at the nanoscale, paving the way for the next generation of photonic and acoustic devices. It underscores the potential for large-scale deployment of silicon photonics by leveraging light-sound interactions to achieve practical and scalable photonic technologies.