Optical simulation, design, and optimization of a microchip-based flow cytometer

The aim of this paper is to improve the functionality and efficiency of a microfluidic device by optically simulating all of the components of the device and then identifying and optimizing the areas of the device where the optics and the microfluidic components overlap. Design of the device will incorporate current advanced methods, such as a state-of-the-art one-shot manufacturing processand noise reduction techniques utilizing 8 parallel waveguides. A suitable material to build this device is the polymer SU-8, which has a refractive index of 1.56 while borofloat glass, refractive index of 1.47, is used as a substrate, and an optical adhesive (Norland Optical Adhesive 74, index of 1.52) is used to seal the device (and serve as the waveguide cladding) by filling the gap in between waveguides reducing scattering losses and confining higher modes. As such, simulations take into account all these parameters. Design of a photomask will take into account three main sources of loss due to the integration of optics and microfluidics: wall thickness, channel thickness, and input angle. Simulations have yielded behaviours and values for these parameters. Wall thickness should be limited to 200um thick which will yield a -5.54dB attenuation (- 2.77dB at the particle) on the input (due to high angular propagation of higher order modes). Input angle of the waveguides (which is crucial to the elimination of signal noise on the output) has been found to reduce output signal noise to -9.60dB at an input angle of 74 degrees to the channel.

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