Efficient light collection for a low-cost respiratory oxygen sensor

Abstract

Fluorescent sensing of oxygen is an optical method for determining the concentration of dissolved or gaseous oxygen in a medium based on flourescent quenching. In the literature, papers on fluorescent quenching oxygen sensor have highlighted certain key problems that limit the sensitivity an disability of these devices. In this paper, we describe a novel optical collection scheme using planar waveguide that overcomes these key issues. The light collection scheme incorporates multiple alterations over the original simple planar waveguide design. These alterations included shearing the end-face of the waveguide, adding reflective coatings, increasing the refractive index of the waveguide material, and finally, tapering one end of the waveguide. The design is modeled and tested using a computer-simulation program. The end result is a light collection scheme that can have a large fluorescing surface are while maintain in a high light collection efficiency. The optimized waveguide is found to guide 7.0% of the total emitted fluorescent power to the detector for an arbitrary surface area of fluorescence material. This design should greatly help to combat a key problem with fluorescent sensing: photo-bleaching.