A Microfluidic Device with an Integrated Waveguide Beam Splitter for Velocity Measurements of Flowing Particles by Fourier Transformation

A microfabricated capillary electrophoresis device for velocity measurements of flowing particles is presented. It consists of a 1 × 128 planar waveguide beam splitter monolithically integrated with an electrically insulated fluidic channel network for fluorescence excitation at multiple points. Stray light rejection structures are included in order to suppress unwanted light between the detection regions. The emission pattern of particles passing the detection region was collected by a photomultiplier tube that was placed in close proximity to the channel, thereby avoiding the use of transfer optics. The integrated planar waveguide beam splitter was, furthermore, permanently connected to the light source by a glued-on optical fiber, to achieve a robust and alignment-free operation of the system. The velocity was measured using a Fourier transformation with a Shah function, since the response of the light array was designed to approximate a square profile. Deviations from this response were observed as a result of the multimode nature of the integrated waveguides.