We demonstrate that the photonic band gaps in silicon slab waveguides are generated through the acousto-optic (AO) interaction. By exciting the acoustic eigenmodes of slab waveguides, the refractive indices and interfaces of silicon slab can be modulated periodically to perturb the guided optical waves and open up the photonic band gaps. We find that the occurrence of the strong forbidden effect to form the band gaps is due to nonlinear interactions between the guided optical and acoustic modes. Using the finite-element method, we calculate the photonic band structures of TE waves and TM waves under the perturbation of the lowest three acoustic eigenmodes, respectively. The results show that the fundamental symmetric acoustic slab mode can create Bragg photonic band gaps of tunable width. With generating acoustic-wave amplitude of 1.0 % of the slab thickness, photonic band gaps from 61.58 – 61.92 THz for TE and 89.10 – 89.24 THz for TM are demonstrated. Applications include the design of optomechanical and AO devices and micro and nanolasers.
Chatter suppression in milling machines, using acoustic signals, is examined for preventing poor finishes and for
upgrading production quality. The technique of on-line acoustic signal analysis for suppressing chatter has been
examined in realistic milling experiments. The natural frequency was determined for end mills, based on finite element
analysis, so that beam equations could be used for chatter detection. Frequency domain analysis was employed to
monitor the shift in the dominant frequency. In this study, the acoustic chatter signal frequency and resonant peak were
applied using a feedback control loop to quantify the acoustic signal and to compensate for spindle speed, respectively.
In micromechanical resonators, energy loss via anchors into the substrates decreases quality factors. To eliminate the
anchor loss, a phononic band-gap structure is proposed and employed. In this paper, we investigate the elastic wave
propagation in phononic crystal strips, cut from a silicon phononic crystal slab consisting of square-lattice vacuum holes,
by analyzing the dispersion relations, acoustic eignemodes, and transmission properties. The phononic crystal strips are
applied to devise the anchor-loss free micromechanical resonators and enhance resonator performances. The phononic
crystal strips are found to have frequency forbidden bands and are introduced to eliminate the anchor loss in the bar-type
and ring-type resonators. Numerical analysis shows that the phononic crystal strips can effectively suppress the acoustic
energy leak and increase the stored energy inside the resonators. Realization of a high quality factor micromechanical
resonator with minimized anchor loss is expected.
Lamb wave propagation in a surface-stubbed phononic-crystal plate is investigated numerically and experimentally.
Results show that the complete band gaps and flat bands of elastic waves exist in the structure. By using laser ultrasonic
techniques, the experimental measurements demonstrate the evidence of the band gaps and resonances at the band-edge
frequencies. In addition, a frequency range associated with the deaf bands is found. Based on the verified band gaps and
deaf bands, waveguiding effects in the structure with a line defect are characterized. Furthermore, a sharply bent
waveguide is then designed and fabricated to experimentally demonstrate frequency selection for broadband Lamb