Versatile liquid-core optofluidic waveguides fabricated in hydrophobic silica aerogels by femtosecond-laser ablation

We report on the fabrication and characterization of optofluidic waveguides exploiting polar liquid filaments confined within hydrophobic silica aerogels. Aerogels are solid materials with low refractive index which can be used as cladding of liquid-core waveguides based on total internal reflection. However, practical applications of aerogels in optofluidics are hampered by their brittleness which renders them difficult to process with conventional machining methods. We introduce a new microfabrication technique that allows precise processing of monolithic silica aerogels by ablation with fs laser pulses. Using this technique, we have succeeded in creating high-quality microchannels with controlled cross-sections which – upon filling with high-refractive index ethylene glycol - formed multimode liquid-core waveguides. Subsequently, we have performed light guiding experiments to measure attenuation of these waveguides. The measured values of propagation losses lower than 10 dB/cm demonstrate that liquid-core waveguides with aerogel cladding represent an attractive alternative in optofluidic applications targeting controlled routing of light along arbitrary three-dimensional paths.