Study On SAW And Their Applications In AOTF

WDM-AONs which build on WDM transfer and OADM, OXC optical node will dominate the new generation optical fiber communications network. OADM is one of the key components of the WDM optical network. The core device of the OADM node is optical filter. In our study, we focus on the OADM based on AOTF.Integrated acousto-optical tunable filters (AOTF), as we know, have many advantages such as wide tunable range, narrow linewidth, fast tuning speed, non-multi-orders diffraction, non-moving parts, easy and reliable tuning and compatible with fiber system. Thus, AOTF attracts wide focus and research.In this paper, we first have a study on the acousto-optic effect media--piezoelectric crystal. And we review some basic knowledge about crystal, such as crystal symmetry, point groups, elastic constant of crystal, dielectric constant, and then piezoelectrical effect includes direct and converse effect. Following, we take the crystal LiNbO₃ for an example to introduce its properties (referring to new material KNbO3 by the way).Secondly, we have a discussion about the propagation characteristics of SAW on the half-space of piezoelectric crystal. Here, we adopt new parameters and numerical computation methods to get the phase velocity of LiNbO3 versus propagation angles under different cuts. Based on the achieved results, we then derive the effective electro-mechanical coupling coefficient, slowness curve, walk-off angle or power flow angle which is indispensable to the design of SAW devices and Acousto-Optic devices. Also, we review the excitation of SAW, the structure of IDT, IDT's simple model, the apodization and weighting technology of IDT, discussion about IDT for AO devices using Green Function Method and so on.Finally, we get into the most important field in our study-AOTF. Especially, we have a study on the AOTF with film-loaded SAW waveguide. Through calculation, we deserve the changes of SAW's velocity and walk-off angle with SiO2 film. These results provide theoretical fundamentals to design new style AOTF.