We report the design, fabrication, and demonstration of single-mode integrated optical waveguides with liquid cores. The principle of the device is based on antiresonant reflecting optical (ARROW) waveguides with hollow cores. We describe design principles for waveguide loss optimization down to 0.1/ cm. Using a fabrication process based on conventional silicon microfabrication and sacrificial core layers, waveguides of varying widths and lengths with volumes covering the pico-to nanoliter

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... were fabricated. We observe confined mode propagation, measure waveguide losses of 2.4/ cm, and demonstrate that the waveguides possess tailorable wavelength selectivity. The potential for highly integrated, sensitive devices based on these properties of the ARROW waveguides is discussed.