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Integrated waveguide biosensors, when combined with fluorescent labeling, have significantly impacted the field of biodetection. While there are numerous types of waveguide sensors, the fundamental excitation method is fairly consistent: the evanescent field of the waveguide excites a fluorophore whose emission is detected, either directly via imaging or indirectly via a decrease in power transfer. Recently, a sensor device was demonstrated which is able to back-couple the emitted light into the waveguide, allowing the signal to be detected directly. However, this previous work focused on the development of an empirical model, leaving many theoretical questions unanswered. Additionally, the results from the novel back-coupling route were not compared with the results from the more conventional imaging technique. In this study, we develop finite difference time domain simulations to predict the sensor's performance both in air and aqueous environments. We also perform complementary experiments to verify the modeling, measuring the fluorescence coupled into the waveguide, and radiated perpendicular to the waveguide. Finally, we performed spatiotemporal measurements of the fluorescence on the waveguide. Utilizing these measurements, we are able to measure the fluorescent decay rate of the fluorescent dye at arbitrary points along the length of the waveguide.