Optomechanical crystals (also referred to as photonic–phononic crystals or phoxonic crystals) exploit the simultaneous photonic and phononic bandgaps in periodic nanostructures. They have been utilized to colocalize, couple, and transduce optical and mechanical (acoustic) waves for nonlinear interactions and precision measurements. Devices that involve standing or traveling acoustic waves of high frequencies usually have advantages in many applications. Here, we review recent progress in nano-optomechanical devices where the acoustic wave oscillates at microwave frequencies. We focus on our development of an optomechanical crystal cavity and a phoxonic crystal waveguide with special features. The development of near-infrared optomechanical crystal cavities has reached a bottleneck in reducing the mechanical modal mass. This is because the reduction of the spatial overlap between the optical and mechanical modes results in a reduced optomechanical coupling rate. With a novel optimization strategy, we have successfully designed an optomechanical crystal cavity in gallium nitride with the optical mode at the wavelength of 393.03 nm, the mechanical mode at 14.97 GHz, the mechanical modal mass of 22.83 fg, and the optomechanical coupling rate of 1.26 MHz. Stimulated Brillouin scattering (SBS) has been widely exploited for applications of optical communication, sensing, and signal processing. A recent challenge of its implementation in silicon waveguides is the weak per-unit-length SBS gain. Taking advantage of the strong optomechanical interaction, we have successfully engineered a phoxonic crystal waveguide structure, where the SBS gain coefficient is greater than 3×10<sup>4</sup> W<sup>−1</sup> m<sup>−1</sup> in the entire C band with the highest value beyond 10<sup>6</sup> <sup>W−1</sup> m<sup>−1</sup>, which is at least an order of magnitude higher than the existing demonstrations.
We develop a unified theory to analyze the modal properties of surface emitting chirped circular grating lasers. Based on
solving the resonance conditions which involve two types of reflectivities of chirped circular gratings, this theory is both
easy to understand and convenient to apply to different configurations of circular grating lasers. Though in a more
concise format, this approach is shown to be in agreement with previous derivations which use the characteristic
equations. With this unified analysis, the modal properties of circular DFB, disk-, and ring- Bragg resonator lasers are
obtained, and the threshold gains, single mode ranges, quality factors, emission efficiencies, and modal areas of these
types of circular grating lasers are compared.
We derive a comprehensive coupled-mode theory, including resonant vertical radiation, for the analysis of non-periodic grating circular Bragg lasers. We analyze the threshold levels and modal properties of such lasers employing mixed-order Bragg gratings to achieve both strong confinement and efficient vertical emission. By reducing the threshold gain and maximizing the emission efficiency, we suggest an optimal design for the circular Bragg microdisk lasers which indicates low-threshold and high-efficiency operation is possible.