Optical Waveguide Design And Fabrication

Kok , Swee Leong and Shafiul, Azam and Mohd Shahril Izuan, Mohd Zin (2005) Optical Waveguide Design And Fabrication. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

In this project. optical planar waveguides were designed by using beam propagation method (BPM). The property of the waveguide which were studied included refractive indices of the glass substrate and waveguide. waveguide width, gap separation between two waveguides, and operational wavelength. The design process started with studying light propagation in a single straight waveguide. S-bended waveguide. a pair of straight waveguide. directional coupler (DC) and followed by more complex waveguide structure, wavelength di vision multiplexer (WDM), which is formed by three different DCs. It was found that light coupling was critically influenced by gap separation between two waveguides. It showed that coupling could be achieved faster when wavelength (A.) to waveguide separation distance (d), /Jd is greater than 1.5. The second part of this project is concerning about the planar waveguide fabrication method. Conventional microelectronic fabrication steps were applied to fabricate SiN-t mask on glass substrate. The steps included photolithography. plasma-enhanced chemical deposition (PECVD) and reactive ion etching (RIE). Waveguide was built in glass substrate by ion-exchange technique, which was done by immersing substrate covered with Si3N4 mask in molten salt of Ag +. K+, and Na +with a composition of 0.0 I :0.5: 0.5 mole % at 250 °C. Ion-exchange activities would take part at the uncovered area of the mask, where ion was diffusing in glass substrate and increased the glass refractive index to 0.07. The time required for ion-exchange process was a crucial factor to control the output power ratio at the output ports. From the Ion-exchange fabrication technique. it was found that side diffusion was an important consideration for mask design. It could be concluded that as far as the device geometry is still in single-mode regime. this ion-exchange fabrication method eliminates the need for high-resolution lithography for producing exact geometry of the device. thus making the process a very economical one.

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