Abstract
The purpose of this paper is to design Mach-Zehnder interferometer (MZI) which is based on the thermo-optical effect (TOE) of the PECVD SiOxNy. The modulation can be achieved by the variation of optical path difference induced by changing of the refractive index of core in waveguide due to TOE. The refractive index (n) of PECVD SiOxNy can be controlled by the mixture of SiH4, N2O and NH3 gases. The required refractive index is 1.478 and 1.47 for core layer and cladding layer, respectively. From the effective index method of 3-D waveguide theory, the dispersion curve for single mode gives the width/thickness ratio of waveguide is about 1 under the consideration of our designed refractive index. So we choose that 5um x 5um channel by concerning the yield of process integration and coupling loss between fiber and waveguide. We use the commercial software called ‘Beam Prop” to simulate the MZI device with length 2000um. There are three waveguide structures: (1) besides core and cladding layers, silicon layer being underneath the cladding layer. (2) besides core and cladding layers, air layer being underneath the cladding layer. (3) an ideal cladding outside the core. Using the structure parameters including the electrode width (Wm), the thickness between electrode and waveguide’s core layer (Th), the distance between waveguide’s core layer and substrate (Tb), switch heating power can be determined. The switch heating power of the case 1 with Wm=5um, Th=5um and Tb=10um, is about 52mW. For the second case, we find that the switch heating power can be largely reduced to 5.5mW about 1/10 compared with case 1. We plan to etch the backside wafer of waveguide to reduce the volume of silicon substrate and prevent the heat loss from conduction in order to get low power consumption. For the case 3, it is the best one in considering the switch power consumption about 1/100 compared with case 1. But it is impractical. Furthermore, we need considering the switch time other than the switch heating power in order to design a workable MZI.