Integration of photonic and passive microfluidic devices into lab-on-chip with femtosecond laser materials processing

Abstract

Femtosecond laser materials processing is a powerful method for the integration of high resolution, 3D structures into Lab-On-Chip (LOC) systems. One major application of femtosecond laser materials processing is waveguide fabrication in glass via index modification. We demonstrate the ability to fabricate couplers and Mach-Zehnder Interferometers (MZI) with good repeatability and flexibility. An in-depth characterization of the spectral characteristics of symmetric directional couplers and MZI is presented. The spectral data from a series of unbalanced MZI is used to characterize changes in the waveguide propagation constant. Towards integrated sensing, we demonstrate the application of femtosecond laser waveguide fabrication to the integration of a MZI into a homemade and commercial LOC for label-free optical detection. The MZI has a unique tilted 3D geometry with one arm crossing a microfluidic channel and enables spatially resolved sensing of changes in the refractive index of the content inside the channel with a limit of detection as low as 1x10 4 RIU. Another major technique in femtosecond laser materials processing is femtosecond two-photon polymerization (TPP). TPP is used to integrate 3D porous filters into a commercial LOC and testing of the filter shows virtually 100% efficient separation of 3 tm polystyrene spheres from a liquid solution. The direct write and maskless nature of femtosecond materials processing makes it a powerful method to integrate 3D devices into LOC without altering existing elements or changing the microfluidic channel fabrication.