We demonstrate the simultaneous existence of slow photonic and phononic modes in phoxonic nanobeam. The phoxonic nanobeam is formed by arranging air semi-cylinders along lateral sides of a suspended silicon waveguide. Because of the slow group velocities, the acousto-optical interactions are dramatically enhanced. The efficiencies of interaction are strongly related to the polarizations of both slow photonic and phononic modes. Our proposed structure is a potential high-efficiency acousto-optical modulator with ultra-small footprint size. The operating optical wavelength is about 1550 nm, while the acoustic frequency is about 6.8 GHz.

The characteristics of biochemical sensors based on photonic crystal (PC) resonators are investigated in this work. The PC structure consists of holes arranged in a hexagonal lattice on a silicon slab. The nanoring resonator is formed by removing certain holes along a hexagonal trace. The hexagonal nanoring resonator is sandwiched by two PC waveguides that are formed by removing two lines of holes. The trapping of biomolecules, e.g., DNAs or proteins, in a functionalized sensing hole introduces a shift in resonant wavelength peak in the output terminal. We demonstrate two resonator designs: single and dual nanorings. The quality factor of the single nanoring resonator is 2400. The dual nanoring resonator reveals two different resonant modes. The propagated directions of dropped light for these two modes are antiparallel. The quality factors for these two resonant modes are 2100 and 1855, respectively. This dual nanoring resonator has a novel sensing mechanism, making it capable of simultaneously sensing two different biomolecules.

We investigate the acousto-optic coupling rates between different acoustic resonance modes and a specified optical resonance mode in a one-dimensional phoxonic crystal fishbone nanobeam formed by periodically arranging semi-cylinders of air on both sides of a suspended silicon waveguide. The gradually tapered unit cells form optical and acoustic resonators. In acousto-optic coupling rate calculation, the acoustic fields and optical fields are obtained by steady state monochromatic analysis and eigen-mode computation, respectively. Results showed that the acoustic polarizations and symmetries of the acoustic resonance modes are dominant factors in the acousto-optic coupling efficiency, and appropriate selection of these parameters can prevent cancellation of acousto-optic interactions, thereby enhancing acousto-optic coupling rates. This study provides important insights that can be applied to acousto-optic device designs.

In recent decades, photonics crystal (PhC), because of its fundamental significance and promising optical performance, has attracted more and more research effort around the world. The ultraconfinement of light in a PhC nanocavity structure in the subwavelength scale, typically in ${(\lambda /n)}^3$ orders, enables the existence of very high quality factor optical localized resonances.¹ Such high confinement of energy in a small volume enables a variety of scientific and engineering applications, such as high-sensitivity sensors,² 3. 4. ^{– 5} ultracompact filters,⁶ 7. 8. ^{– 9} fast modulators,¹⁰ low-power all-optical switches,¹¹ and tunable optical resonators.^12,13 By extending the cavity defect in the PhC to a line defect of missing air holes, a PhC waveguide is created and works in the slow-light regime.¹⁴ The PhC waveguide allows the propagation of certain wavelengths of light which are confined by total internal reflection and Bragg reflection in the lateral direction. However, the PhC waveguide slows down the light traveling speed and results in a strong localized electrical field. By employing optical dispersion engineering to address the loss limitation feature of the slow light, it enables slow-light designs to play a key role in all-optical circuit-related applications, such as all-optical storage, switching, and data regeneration in telecommunications. Slow light also enhances the nonlinear optical effect in the PhC waveguide, as the intensity scales with the slowdown factor.^15,16 The strong localized electric field of the slow-light region also enables and enhances liquid and gas sensing.^17,18 High-order dispersion usually occurs and distorts the optical signals in the case of devices having a long optical path. To eliminate such distortion, several zero-dispersion devices were developed.¹⁹ 20. 21. 22. ^{– 23} Moreover, a coupled-resonator optical waveguide based on PhC cavities or microrings can also help in compensation of the slow-light device distortions.^24,25

We investigate theoretically and experimentally the absorption of a Helmholtz resonator (HR) array, an aluminum device operated in water. The HR array’s period is 2 mm. The operating frequency range is ∼0.2–0.7 MHz. We observed two transmission dips in both experimental and theoretical spectra. These dips are dominated by different resonance orders in the HR. The resonance behaviors are investigated with steady-fields simulation and can be represented by spring-mass models. This allows us to reduce the device’s footprint significantly.