3D Printing Optofluidic Mach-Zehnder Interferometer on a Fiber Tip for Refractive Index Sensing

An optofluidic polymer Mach-Zehnder interferometer (MZI) fabricated via direct laser writing (DLW) on a fiber tip is proposed and experimentally demonstrated as a refractometer where one of the interference arms is made of the polymer waveguide while the other arm is a hollow cavity with a 1-μm wall thickness and containing two open channels. The analytes can be filled through the channels, forming an optofluidic component of the interferometer. In this letter, two MZI microstructures with different hollow lengths are described and characterized. The experimental results of the two MZIs in air and water show that the MZI with a longer hollow cavity has higher sensitivity. Analytes such as de-ionized (DI) water and glucose solutions with different concentrations have been measured in the MZI with the long hollow cavity. The results show that this kind of sensing device provides a promising platform for refractive index measurements with a sensitivity of 593.75 nm/RIU based on the FSR calculation method.