3D printed optical system based on Digital Light Processing technology for sensing applications

Abstract

This research demonstrates the design, fabrication and development of a simple and practical cost-effective optical waveguide system by making use of 3D printing Digital Light Processing technology for sensing applications. The cost is minimized by utilizing 3D printing Fused Deposition Method technology to print the mechanical components involved. This research involves a new approach to fabricate a single-step integrated optical waveguide system where strong light confinement in the ridge (guiding) section of the fabricated structure is realized through the introduction of an elevated (tower-shaped) waveguide in a transparent photosensitive resin (PX-8880) with refractive index n=1.47. This fabrication scheme is optimized to maximize light confinement through varying the dimensions of the guiding region and the tower structure. The FEM simulation with the desired parameters of the fabricated structure performed showed strong light confinement in the guiding region. Benefiting from the surface roughness produced by the slicing process in the 3D printing DLP technology (50μm resolution), the fabricated structure was tested for vapor sensing. Intensity dynamics responses are achieved due to the change of the optical scattering from the presence of vapor as well as polymer resin vapor interaction where it displayed a potential to implement it as a sensor. Further optimization of the fabricated structure was enhanced by introducing a gap in the ridge region of waveguide system and it is implemented as a practical isopropanol alcohol (IPA) concentration sensor without in need of a vacuum system. This is also done by designing and fabricating using 3D printing DLP technology using photosensitive MonoCure 3D Rapid UV clear resin with the refractive index n=1.50. Various waveguides with different gap size along the horizontal region (guiding region) were printed and comparisons were performed for the several gap sizes including the structure without the gap by implementing re-coupling of light concept and swelling characteristics of the photopolymer resin resulting in higher transmitted light power/intensity in the presence of alcohol. Three different concentrations (2.5µl, 5µl and 10µl) of IPA was used for testing with the fabricated structures. The parameters investigated are the dimensions of the waveguide gap with its overall structure and the sensor chamber. The waveguide gap size of 300µm displayed the strong confinement at the ridge region with the increase in transmitted optical power for 65% when tested with 10µl (500ppm) concentration of IPA and faster response time in increasing transmitted optical power rise after depositing IPA in the sensor chamber for t=5 seconds compared to all the gaps with Limit of Detection (LOD) of 0.366µl. In addition, the fabricated waveguide gap structure of 300µm demonstrated the sensing limit of IPA concentration below 400ppm which is considered as an exposure limit by “National Institute for Occupational Safety and Health”. Thus, the fabricated optical system successfully demonstrated its usefulness with its ease of fabrication using 3D printing DLP technology and proved as a sensor where the dimensions are in hundreds of microns.