Piezoelectric resonance enhanced microwave and optoelectronic interactive devices
Electro-optic (EO) devices that modulate optical signals by electric fields are an integrative part of the photonics industry and device optimization is an important area of research. As applications move to large bandwidth and higher frequency, low electro-optic effects and the requirement for large dimension become restrictive for microwave-optical devices. Both experimental and computational evaluations indicate that strain and polarization distribution have a significant impact on electromagnetic wave propagation resulting from a resonant structure; however, no systematic study or fundamental understandings are available.
This dissertation research has been carried out to study and further develop the subject of piezoelectric resonance enhanced electro-acoustic-optic process, in order to improve the sensitivity and efficiency of electro-optic sensors and to explore novel applications. Many finite element models have been constructed for evaluating the mechanisms of the phenomena and the effectiveness of the device structure. The enhancement in transmission is found to be directly related to the strain-coupled local polarization. At piezoelectric resonance oscillating dipoles or local polarizations become periodic in the material and have the greatest impact on transmission. Results suggest that the induced charge distribution by a piezoelectric material at certain resonant frequencies is effective for aiding or impeding the transmission of a propagating wave. The behavior of both piezoelectric-defined (or intrinsic piezoelectric materials) and engineered periodic structures are reported. The piezoelectric response of the surface displacement of samples is investigated using an ultra-high frequency laser Doppler vibrometer. A two dimensional view of the surface is obtained and the surface displacement, velocity and acceleration are compared to the electro-optic response under the resonant condition. A study of the acousto-optic (AO) effect in a family of oxide crystals (including e.g., TiO 2, ZnO, LiNbO3, and ferroelectric perovskites) has been conducted by the finite element analysis method. This study further serves to show the potential of optimizing devices through a consideration of their directional dependent parameters and resonant behavior. The acousto-optic figure of merit (FOM) as a function of the material's refractive index, density, effective AO coefficient and the velocity of the acoustic wave in the material, is also investigated. By examining the directional dependent velocity, acousto-optic coefficients, and refractive index, the acousto-optic FOM can be calculated and plotted in all directions revealing the optimal crystal orientation to maximize coupling between the optical and acoustic waves. A finite element model was developed to corroborate the improved interaction. The model examines the diffraction that occurs on the optical wave as it travels through an acousto-optic medium. The combined information gained from commercially available multiphysics-based modeling platforms is shown to be an effective means of predicating acousto-optic device functionality.