Low-loss liquid-core optical fiber for low-refractive-index liquids: fabrication, characterization, and application in Raman spectroscopy

We describe a liquid-core optical fiber based on capillary tubing of Teflon AF 2400, which is a clear, amorphous fluoropolymer having a refractive index of 1.29. When filled with virtually any transparent liquid, the fiber is capable of transmitting light by total internal reflection. Loss below 3 dB/microm is demonstrated throughout much of the visible region for a 250-microm-i.d. fiber filled with water. The utility of this device in enhancing the intensity of Raman spectra of core liquids is demonstrated.