Integrated ARROW waveguides for gas/liquid sensing

We present integrated antiresonant reflecting optical (ARROW) structures with hollow cores as a new paradigm for optical sensing of gases and liquids. ARROW waveguides with micron-sized hollow cores allow for single-mode propagation in low-index non-solid core materials where conventional index guiding is impossible. We review design, fabrication and optical characterization of these devices for possible applications in chemical sensing, single molecule fluorescence and Raman spectroscopy, flow cytometry, and pollution monitoring of picoliter to nanoliter volumes. We describe how to determine and control the waveguide loss and dispersion of the ARROW waveguides and design optimization for realistic structures that are compatible with the fabrication constraints. The technology to realize hollow-core waveguides using conventional silicon microfabrication and sacrificial core layers is discussed. We present the first demonstration of waveguiding in integrated ARROW waveguides with both hollow and liquid cores. Single-mode propagation with mode areas as small as 6mum(2) and volumes down to 15 picoliters is observed and the loss characteristics of the waveguides are determined. The observation of fluorescence from dye molecules with concentrations of 10 nmol/l is described. Higher-level integration towards compact, planar, and massively parallel sensors on a chip is discussed.