Double-coupled slotted photonic crystal slab cavities through a high-frequency mechanical oscillator

Scalability is a critical research direction at the current stage of optomechanics for on-chip-integrated telecommunications and fundamental research, such as topological physics. Achieving scalability requires the coupling of multiple cavities via mechanical oscillators or the coupling of multiple oscillators via optical cavities. The optomechanical system proposed in this paper consists of two slotted silicon photonic crystal (PhC) slab cavities, where the optical barrier between the two cavities acts as a silicon mechanical oscillator, facilitating their coupling. This is the first two-dimensional (slab) PhC configuration featuring distant cavities coupled via a high-frequency (up to gigahertz) mechanical oscillator. This system offers two advantages over previous localized multimode optomechanical cavities. First, it allows for the independent design of the two cavities at desired resonance wavelengths. Second, the optical signals from the two cavities are coupled to different optical channels, simplifying post-processing tasks such as filtering or demultiplexing in photonic integrated circuits. Moreover, the slab optomechanical configuration could serve as a potential silicon alternative to compound-semiconductor slab optical switches and memories. Our numerical investigation shows that both cavities can be designed with ultrahigh quality factors and that the swing and breathing mechanical resonance modes exhibit the strongest optomechanical coupling strength. Notably, as far as we know, this is the first demonstration of an optomechanical breathing mode in 2D PhC structures, with a frequency reaching up to one gigahertz. Finally, we discuss two potential applications for this system: a pseudo-all-optical switch/modulator and resolved sideband operation. These analyses demonstrate that the proposed system holds significant promise for meeting the stringent requirements of various applications in photonic integrated circuits and photonic quantum technologies.