Bulk-Silicon-Based Waveguides and Bends Fabricated Using Silicon Wet Etching: Properties and Limits

We develop a process of fabricating silicon waveguides and devices using a bulk silicon substrate. The fabrication process mainly consists of one silicon dry etching and one silicon wet etching. The use of silicon wet etching makes the process simple and inexpensive. Because of the anisotropic nature of silicon wet etching, the bulk-silicon-based (BSB) waveguide made by the process consists of an inverted-trapezoidal core on a rectangular pedestal and a trapezoidal base beneath the pedestal. In addition, geometrically smooth BSB waveguide bends can be achieved when the radii of curvature of the bends are sufficiently large. The propagation loss of the BSB waveguide depends on wet etching conditions and it is 4.0 or 0.79 dB/cm for transverse-magnetic polarization. It is confirmed that the minimum radius of curvature of the BSB waveguide bend is 500 μm. The BSB waveguides and bends are expected to be used to implement low-cost sensors with simple geometry.