Advances in integrated hollow waveguides for on-chip sensors

We have previously produced antiresonant reflecting optical waveguides (ARROWs) with hollow cores that can guide light through liquid or gas media. In order to utilize these structures in sophisticated sensing applications, we have improved our initial designs and fabrication methods to increase yield, lower waveguide transmission loss, and incorporate structural features into the waveguides themselves. Yields have been increased by optimizing PECVD film conformality leading to greater sidewall strength for hollow waveguides. Sensing applications require interfacing hollow waveguides with solid waveguides on the surface of a substrate to direct light on and off a chip and into and out of a test medium. Previous interfaces required light transferring from solid to hollow waveguides to pass through the antiresonant layers, with measured transmission efficiencies of about 30%. By removing the ARROW layers at the interfaces, transmission efficiencies at these interfaces can be improved to greater than 95%. We also demonstrate the fabrication of micropore structures on the hollow waveguides to be used for chemical sensing. A fabrication method has been developed that allows for removal of the thick top oxide and nitride ARROW layers leaving only a thin nitride membrane directly over the hollow core allowing controlled access to test media.