A Comprehensive Investigation of a Microfabricated U-Bend Polymer Waveguide With Analyte Micro-Reservoir for Versatile On-Chip Sensing Applications

In our earlier designed, embedded U-shaped-waveguides, due to lower area of analyte interaction, there was always a scope to simplify and modify the device design to improve its evanescent-absorbance sensitivity. To achieve this objective, a simple designed micro-analysis chips consisting of a U-bend waveguide probes coupled microreservoir structure were theoretically and experimentally investigated in this paper. For the fabrication of these microstructures along with fiber-to-waveguide-coupler structures, a single-step micro-fabrication procedure was performed using SU-8 photoresist. Initially, in this paper, using suitable numerical-calculations, we have also focused on the analyzing various physical parameters, which contribute to their sensitivity, which further corroborated with the experimental results. Furthermore, we recognized the effect of cross-coupling phenomenon (between their two straight-arms) to be a reason for lower RI-sensitivity, as well as linear and higher evanescent-absorption-based detection sensitivity for lower bending-diameter (< 0.5 mm) waveguide. Compared with embedded U-bend waveguides, the overall evanescent-absorption sensitivity of U-bend waveguides was found improved by approximately three times. Finally, it proved to be a useful flexible sensing-probe for any physical, chemical, and biological sensing application, provided appropriate surface modification is made to this waveguide probe