In this paper we report a novel fabrication technique for silicon photonic waveguides with sub-micron dimensions. The
technique is based upon the Local Oxidation of Silicon (LOCOS) process widely utilised in the fabrication of
microelectronics components. This approach enables waveguides to be fabricated with oxide sidewalls with minimal
roughness at the silicon/SiO2 interface. It is also sufficiently flexible to enable the depth of the oxidised sidewall to be
varied to control the polarisation performance of the waveguides.
We will present preliminary results on submicron waveguide fabrication and loss characteristics (less than 1 dB/cm), as
well as effects of varying waveguide width on modal properties of the waveguides. We consider the ease of fabrication,
as well as the quality of the devices produced in preliminary experimental fabrication results, and compare the approach
to the more conventional requirements of high resolution photolithographically produced waveguides. We also discuss
preliminary optical results, as measured by conventional means. Issues such as the origins of loss are discussed in
general terms, as are the fabrication characteristics such as waveguide wall roughness and waveguide profile. We will
discuss further work that will help to establish the potential of the technique for future applications.
The Local Oxidation of Silicon (LOCOS) technique is used to define optical rib waveguides in silicon-on-insulator
(SOI) material. This process, commonly used for device isolation in purely microelectronic CMOS processes, results in
a nearly planar surface suitable for integrating optical and electronic components on the same chip. Optical mode
simulation was used to determine rib geometries suitable for single-mode propagation and minimizing birefringence in
the 1550 nm optical telecommunications band. Test devices were then fabricated in SOI material with a Si film
thickness near 3 microns. Growth of a 1 micron field oxide by wet oxidation yielded a 0.5 micron rib height. As-drawn rib widths
ranged from 3 microns to 5 microns, giving final rib widths ranging from 2 microns to 4 microns after oxidation. Cutback optical testing of 3 microns drawn width ribs showed the loss to be less than 1 dB/cm at 1555 nm. Unbalanced Mach-Zehnder interferometers
with Y-splitter junctions were also fabricated and tested with input wavelength swept from 1470 to 1580 nm and showed
an extinction of 6-10 dB, demonstrating the ability of the LOCOS rib technique to produce more complex waveguide
devices.
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