Maria Bayard Dühring - Solid Mechanics

38 Chapter 6 Design of acousto-optical interaction [P3]-[P7]
Figure 6.3 Generation of a Rayleigh wave in a GaAs sample. The position of the interdigital
transducer (IDT) is indicated. (a): The color indicates the displacement u2 and the
surface is deformed with the unified displacements u1 and u2. (b): The absolute amplitude
|u2| along the material surface. (c): The electrical potential V along the material surface.
cases in order to explain the difference in performance. The geometry used in the
simulations is sketched in figure 6.2(b). In both cases the SAW is generated by
six double electrode finger pairs, and each of the electrodes has a width equal to
0.7 µm and is placed 0.7 µm apart such that the wavelength of the generated SAW
is 5.6 µm. To the right the Rayleigh wave will pass through the two waveguides
where the optical waves are confined due to the air and the layer below that consists
of another material. In the case of the GaAs/AlGaAs sample the confining layer
consists of Al0.2Ga0.8As, which will be referred to as AlGaAs in the following. The
waveguides have the width 1.4 µm and the height 0.3 µm. The driving frequency
is f = 518 MHz and the optical wavelength is λ0 = 950 nm. In the SOI case
the substrate and the waveguides are made of Si and the confining layer is SiO2.
These materials are not piezoelectric so the electrodes are placed on top of a ZnO
layer from where the generated SAW propagates to the rest of the sample. The
waveguides have the width 0.45 µm and the height 0.34 µm. The driving frequency
is f = 630 MHz and the optical wavelength is λ0 = 1531 nm. In [P4] the values
of the un-rotated stress-optical constants C44, C55 and C66 for Si have been ignored