Hollow core micro-fiber for optical wave guiding and microfluidic manipulation

We report the fabrication and characterization of hollow core micro-fibers (HCMFs) for use as optical waveguides and microfluidic channels meanwhile. By one-step heating-drawing process from commercial capillary with diameter of hundreds of micrometers, HCMFs with diameters down to subwavelength scale can be fabricated with excellent repeatability. The HCMFs reveal good optical waveguide properties as waveguides with low optical losses by evanescently coupled from silica fiber taper within the visible to near-infrared spectral range. Meanwhile, the wavelength-scale-diameter hollow core of the HCMF can be used as a microfluidic channel to host liquid with trace amounts, which has an intense interaction with the guiding light. Flexible waveguide properties and different fractions of evanescent fields of HCMFs can be achieved by filling the core with various liquids with different refractive indexes (RIs), which might be useful in various applications. For example, we use our HCMF to detect the fluorescence intensity for monodisperse micro-particles solutions with an effective detection volume of femtoliter scale. Our work provides a promising candidate in constructing miniaturized optical devices, which can be used for detection of ultra-low-volume samples.