Fabrication of hollow waveguides with sacrificial aluminum cores

We have developed a process to fabricate dielectric waveguide structures with long hollow cores formed by etching a sacrificial core material. The process is compatible with other planar silicon fabrication techniques. Using aluminum as the sacrificial material, we have investigated fabrication limits and design parameters that determine mechanical integrity of the waveguides. Internal pressure due to the production of gaseous compounds during the core removal process was identified as the yield-limiting factor. A mechanical model based on finite element analysis and confirmed by experiment, predicts ultimate pressures sustainable by these structures. Waveguides less than 10 μm wide with 2-μm-thick coatings should sustain 50 MPa of internal pressure. Low-loss guided-mode propagation in optical waveguides based on these hollow cores is demonstrated.