Demonstration of a Polymer-Based Single Step Waveguide by 3D Printing Digital Light Processing Technology for Isopropanol Alcohol-Concentration Sensor

A polymer based horizontal single step waveguide for the sensing of alcohol is developed and analyzed. The waveguide is fabricated by 3-dimensional (3D) printing digital light processing (DLP) technology using monocure 3D rapid ultraviolet (UV) clear resin with a refractive index of n = 1.50. The fabricated waveguide is a one-piece tower shaped ridge structure. It is designed to achieve the maximum light confinement at the core by reducing the effective refractive index around the cladding region. With the surface roughness generated from the 3D printing DLP technology, various waveguides with different gap sizes are printed. Comparison is done for the different gap waveguides to achieve the minimum feature gap size utilizing the light re-coupling principle and polymer swelling effect. This effect occurs due to the polymer-alcohol interaction that results in the diffusion of alcohol molecules inside the core of the waveguide, thus changing the waveguide from the leaky type (without alcohol) to the guided type (with alcohol). Using this principle, the analysis of alcohol concentration performing as a larger increase in the transmitted light intensity can be measured. In this work, the sensitivity of the system is also compared and analyzed for different waveguide gap sizes with different concentrations of isopropanol alcohol (IPA). A waveguide gap size of 300 mu m gives the highest increase in the transmitted optical power of 65% when tested with 10 mu L (500 ppm) concentration of IPA. Compared with all other gaps, it also displays faster response time (t = 5 seconds) for the optical power to change right after depositing IPA in the chamber. The measured limit of detection (LOD) achieved for 300 mu m is 0.366 mu L. In addition, the fabricated waveguide gap of 300 mu m successfully demonstrates the sensing limit of IPA concentration below 400 ppm which is considered as an exposure limit by National Institute for Occupational Safety and Health. All the mechanical mount and the alignments are done by 3D printing fused deposition method (FDM).

Automated summary

A polymer-based horizontal single-step waveguide for alcohol sensing was developed and analyzed using 3D printing DLP technology. The waveguide structure is designed for maximum light confinement at the core and utilizes the interaction between polymer and alcohol for detection. By comparing different waveguide gap sizes, it was found that a gap size of 300 μm showed the highest increase in transmitted optical power when tested with isopropanol alcohol concentration of 500 ppm.