Hollow core waveguides, wherein light is confined in a low index gas or liquid medium, have many applications in spectroscopy, bioanalytics, nonlinear optics, and sensing.  A novel hollow core waveguide, the light cage, was recently demonstrated in a collaboration between groups in Germany and England.  It consists of a free-standing array of high index polymer cylinders, fabricated by 3D laser nanoprinting, surrounding a hollow core.  Light is guided by anti-resonant scattering from the cylinders, so the transmission spectrum consists of discrete wavelength bands spanning the visible and near-infrared.  The spectral position of these bands depends on the diameter and index contrast of the cylinders.  The light cage is unique in that it has an open geometry, so that the core can be filled with gases or liquids orders of magnitude faster than traditional hollow waveguides where the core is completely surrounded.  In their most recent paper published in Optical Materials Express, the authors demonstrate light cages up to 3 cm in length with transmission losses on the order of 0.5-1 dB/mm, comparable to the state-of-the-art for on-chip hollow core waveguides.  They investigate the reproducibility of their manufacturing technique and show that multiple light cages fabricated on a single chip exhibit only nanometer variation in the cylinder diameter, so that all the waveguides have similar transmission spectra and loss.  For waveguides produced on different chips, the variation is greater, on the order of 15 nm, which they attribute to variations in the polymer development process.  These results demonstrate that the light cage is a promising platform for high-throughput chip-based optical sensing and analysis.

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